Bug Summary

File:src/gnu/usr.bin/clang/liblldELF/../../../llvm/lld/ELF/Writer.cpp
Warning:line 1914, column 29
Called C++ object pointer is null

Annotated Source Code

Press '?' to see keyboard shortcuts

clang -cc1 -cc1 -triple amd64-unknown-openbsd7.0 -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name Writer.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -mrelocation-model static -mframe-pointer=all -relaxed-aliasing -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -fcoverage-compilation-dir=/usr/src/gnu/usr.bin/clang/liblldELF/obj -resource-dir /usr/local/lib/clang/13.0.0 -I /usr/src/gnu/usr.bin/clang/liblldELF/obj/../include/lld/ELF -I /usr/src/gnu/usr.bin/clang/liblldELF/../../../llvm/lld/include -I /usr/src/gnu/usr.bin/clang/liblldELF/../../../llvm/lld/ELF -I /usr/src/gnu/usr.bin/clang/liblldELF/../../../llvm/llvm/include -I /usr/src/gnu/usr.bin/clang/liblldELF/../include -I /usr/src/gnu/usr.bin/clang/liblldELF/obj -I /usr/src/gnu/usr.bin/clang/liblldELF/obj/../include -D NDEBUG -D __STDC_LIMIT_MACROS -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D LLVM_PREFIX="/usr" -internal-isystem /usr/include/c++/v1 -internal-isystem /usr/local/lib/clang/13.0.0/include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir=/usr/src/gnu/usr.bin/clang/liblldELF/obj -ferror-limit 19 -fvisibility-inlines-hidden -fwrapv -stack-protector 2 -fno-rtti -fgnuc-version=4.2.1 -vectorize-loops -vectorize-slp -fno-builtin-malloc -fno-builtin-calloc -fno-builtin-realloc -fno-builtin-valloc -fno-builtin-free -fno-builtin-strdup -fno-builtin-strndup -analyzer-output=html -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /home/ben/Projects/vmm/scan-build/2022-01-12-194120-40624-1 -x c++ /usr/src/gnu/usr.bin/clang/liblldELF/../../../llvm/lld/ELF/Writer.cpp

/usr/src/gnu/usr.bin/clang/liblldELF/../../../llvm/lld/ELF/Writer.cpp

1//===- Writer.cpp ---------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "Writer.h"
10#include "AArch64ErrataFix.h"
11#include "ARMErrataFix.h"
12#include "CallGraphSort.h"
13#include "Config.h"
14#include "LinkerScript.h"
15#include "MapFile.h"
16#include "OutputSections.h"
17#include "Relocations.h"
18#include "SymbolTable.h"
19#include "Symbols.h"
20#include "SyntheticSections.h"
21#include "Target.h"
22#include "lld/Common/Arrays.h"
23#include "lld/Common/Filesystem.h"
24#include "lld/Common/Memory.h"
25#include "lld/Common/Strings.h"
26#include "llvm/ADT/StringMap.h"
27#include "llvm/ADT/StringSwitch.h"
28#include "llvm/Support/Parallel.h"
29#include "llvm/Support/RandomNumberGenerator.h"
30#include "llvm/Support/SHA1.h"
31#include "llvm/Support/TimeProfiler.h"
32#include "llvm/Support/xxhash.h"
33#include <climits>
34
35#define DEBUG_TYPE"lld" "lld"
36
37using namespace llvm;
38using namespace llvm::ELF;
39using namespace llvm::object;
40using namespace llvm::support;
41using namespace llvm::support::endian;
42using namespace lld;
43using namespace lld::elf;
44
45namespace {
46// The writer writes a SymbolTable result to a file.
47template <class ELFT> class Writer {
48public:
49 LLVM_ELF_IMPORT_TYPES_ELFT(ELFT)using Elf_Addr = typename ELFT::Addr; using Elf_Off = typename
ELFT::Off; using Elf_Half = typename ELFT::Half; using Elf_Word
= typename ELFT::Word; using Elf_Sword = typename ELFT::Sword
; using Elf_Xword = typename ELFT::Xword; using Elf_Sxword = typename
ELFT::Sxword; using uintX_t = typename ELFT::uint; using Elf_Ehdr
= typename ELFT::Ehdr; using Elf_Shdr = typename ELFT::Shdr;
using Elf_Sym = typename ELFT::Sym; using Elf_Dyn = typename
ELFT::Dyn; using Elf_Phdr = typename ELFT::Phdr; using Elf_Rel
= typename ELFT::Rel; using Elf_Rela = typename ELFT::Rela; using
Elf_Relr = typename ELFT::Relr; using Elf_Verdef = typename ELFT
::Verdef; using Elf_Verdaux = typename ELFT::Verdaux; using Elf_Verneed
= typename ELFT::Verneed; using Elf_Vernaux = typename ELFT::
Vernaux; using Elf_Versym = typename ELFT::Versym; using Elf_Hash
= typename ELFT::Hash; using Elf_GnuHash = typename ELFT::GnuHash
; using Elf_Nhdr = typename ELFT::Nhdr; using Elf_Note = typename
ELFT::Note; using Elf_Note_Iterator = typename ELFT::NoteIterator
; using Elf_CGProfile = typename ELFT::CGProfile; using Elf_BBAddrMap
= typename ELFT::BBAddrMap; using Elf_Dyn_Range = typename ELFT
::DynRange; using Elf_Shdr_Range = typename ELFT::ShdrRange; using
Elf_Sym_Range = typename ELFT::SymRange; using Elf_Rel_Range
= typename ELFT::RelRange; using Elf_Rela_Range = typename ELFT
::RelaRange; using Elf_Relr_Range = typename ELFT::RelrRange;
using Elf_Phdr_Range = typename ELFT::PhdrRange;
50
51 Writer() : buffer(errorHandler().outputBuffer) {}
52
53 void run();
54
55private:
56 void copyLocalSymbols();
57 void addSectionSymbols();
58 void forEachRelSec(llvm::function_ref<void(InputSectionBase &)> fn);
59 void sortSections();
60 void resolveShfLinkOrder();
61 void finalizeAddressDependentContent();
62 void optimizeBasicBlockJumps();
63 void sortInputSections();
64 void finalizeSections();
65 void checkExecuteOnly();
66 void setReservedSymbolSections();
67
68 std::vector<PhdrEntry *> createPhdrs(Partition &part);
69 void addPhdrForSection(Partition &part, unsigned shType, unsigned pType,
70 unsigned pFlags);
71 void assignFileOffsets();
72 void assignFileOffsetsBinary();
73 void setPhdrs(Partition &part);
74 void checkSections();
75 void fixSectionAlignments();
76 void openFile();
77 void writeTrapInstr();
78 void writeHeader();
79 void writeSections();
80 void writeSectionsBinary();
81 void writeBuildId();
82
83 std::unique_ptr<FileOutputBuffer> &buffer;
84
85 void addRelIpltSymbols();
86 void addStartEndSymbols();
87 void addStartStopSymbols(OutputSection *sec);
88
89 uint64_t fileSize;
90 uint64_t sectionHeaderOff;
91};
92} // anonymous namespace
93
94static bool isSectionPrefix(StringRef prefix, StringRef name) {
95 return name.startswith(prefix) || name == prefix.drop_back();
96}
97
98StringRef elf::getOutputSectionName(const InputSectionBase *s) {
99 if (config->relocatable)
100 return s->name;
101
102 // This is for --emit-relocs. If .text.foo is emitted as .text.bar, we want
103 // to emit .rela.text.foo as .rela.text.bar for consistency (this is not
104 // technically required, but not doing it is odd). This code guarantees that.
105 if (auto *isec = dyn_cast<InputSection>(s)) {
106 if (InputSectionBase *rel = isec->getRelocatedSection()) {
107 OutputSection *out = rel->getOutputSection();
108 if (s->type == SHT_RELA)
109 return saver.save(".rela" + out->name);
110 return saver.save(".rel" + out->name);
111 }
112 }
113
114 // A BssSection created for a common symbol is identified as "COMMON" in
115 // linker scripts. It should go to .bss section.
116 if (s->name == "COMMON")
117 return ".bss";
118
119 if (script->hasSectionsCommand)
120 return s->name;
121
122 // When no SECTIONS is specified, emulate GNU ld's internal linker scripts
123 // by grouping sections with certain prefixes.
124
125 // GNU ld places text sections with prefix ".text.hot.", ".text.unknown.",
126 // ".text.unlikely.", ".text.startup." or ".text.exit." before others.
127 // We provide an option -z keep-text-section-prefix to group such sections
128 // into separate output sections. This is more flexible. See also
129 // sortISDBySectionOrder().
130 // ".text.unknown" means the hotness of the section is unknown. When
131 // SampleFDO is used, if a function doesn't have sample, it could be very
132 // cold or it could be a new function never being sampled. Those functions
133 // will be kept in the ".text.unknown" section.
134 // ".text.split." holds symbols which are split out from functions in other
135 // input sections. For example, with -fsplit-machine-functions, placing the
136 // cold parts in .text.split instead of .text.unlikely mitigates against poor
137 // profile inaccuracy. Techniques such as hugepage remapping can make
138 // conservative decisions at the section granularity.
139 if (config->zKeepTextSectionPrefix)
140 for (StringRef v : {".text.hot.", ".text.unknown.", ".text.unlikely.",
141 ".text.startup.", ".text.exit.", ".text.split."})
142 if (isSectionPrefix(v, s->name))
143 return v.drop_back();
144
145 for (StringRef v :
146 {".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.rel.ro.",
147 ".bss.", ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
148 ".gcc_except_table.", ".tdata.", ".ARM.exidx.", ".ARM.extab.",
149 ".openbsd.randomdata."})
150 if (isSectionPrefix(v, s->name))
151 return v.drop_back();
152
153 return s->name;
154}
155
156static bool needsInterpSection() {
157 return !config->relocatable && !config->shared &&
158 !config->dynamicLinker.empty() && script->needsInterpSection();
159}
160
161template <class ELFT> void elf::writeResult() {
162 Writer<ELFT>().run();
163}
164
165static void removeEmptyPTLoad(std::vector<PhdrEntry *> &phdrs) {
166 auto it = std::stable_partition(
167 phdrs.begin(), phdrs.end(), [&](const PhdrEntry *p) {
168 if (p->p_type != PT_LOAD)
169 return true;
170 if (!p->firstSec)
171 return false;
172 uint64_t size = p->lastSec->addr + p->lastSec->size - p->firstSec->addr;
173 return size != 0;
174 });
175
176 // Clear OutputSection::ptLoad for sections contained in removed
177 // segments.
178 DenseSet<PhdrEntry *> removed(it, phdrs.end());
179 for (OutputSection *sec : outputSections)
180 if (removed.count(sec->ptLoad))
181 sec->ptLoad = nullptr;
182 phdrs.erase(it, phdrs.end());
183}
184
185void elf::copySectionsIntoPartitions() {
186 std::vector<InputSectionBase *> newSections;
187 for (unsigned part = 2; part != partitions.size() + 1; ++part) {
188 for (InputSectionBase *s : inputSections) {
189 if (!(s->flags & SHF_ALLOC) || !s->isLive())
190 continue;
191 InputSectionBase *copy;
192 if (s->type == SHT_NOTE)
193 copy = make<InputSection>(cast<InputSection>(*s));
194 else if (auto *es = dyn_cast<EhInputSection>(s))
195 copy = make<EhInputSection>(*es);
196 else
197 continue;
198 copy->partition = part;
199 newSections.push_back(copy);
200 }
201 }
202
203 inputSections.insert(inputSections.end(), newSections.begin(),
204 newSections.end());
205}
206
207void elf::combineEhSections() {
208 llvm::TimeTraceScope timeScope("Combine EH sections");
209 for (InputSectionBase *&s : inputSections) {
210 // Ignore dead sections and the partition end marker (.part.end),
211 // whose partition number is out of bounds.
212 if (!s->isLive() || s->partition == 255)
213 continue;
214
215 Partition &part = s->getPartition();
216 if (auto *es = dyn_cast<EhInputSection>(s)) {
217 part.ehFrame->addSection(es);
218 s = nullptr;
219 } else if (s->kind() == SectionBase::Regular && part.armExidx &&
220 part.armExidx->addSection(cast<InputSection>(s))) {
221 s = nullptr;
222 }
223 }
224
225 std::vector<InputSectionBase *> &v = inputSections;
226 v.erase(std::remove(v.begin(), v.end(), nullptr), v.end());
227}
228
229static Defined *addOptionalRegular(StringRef name, SectionBase *sec,
230 uint64_t val, uint8_t stOther = STV_HIDDEN,
231 uint8_t binding = STB_GLOBAL) {
232 Symbol *s = symtab->find(name);
233 if (!s || s->isDefined())
234 return nullptr;
235
236 s->resolve(Defined{/*file=*/nullptr, name, binding, stOther, STT_NOTYPE, val,
237 /*size=*/0, sec});
238 return cast<Defined>(s);
239}
240
241static Defined *addAbsolute(StringRef name) {
242 Symbol *sym = symtab->addSymbol(Defined{nullptr, name, STB_GLOBAL, STV_HIDDEN,
243 STT_NOTYPE, 0, 0, nullptr});
244 return cast<Defined>(sym);
245}
246
247// The linker is expected to define some symbols depending on
248// the linking result. This function defines such symbols.
249void elf::addReservedSymbols() {
250 if (config->emachine == EM_MIPS) {
251 // Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
252 // so that it points to an absolute address which by default is relative
253 // to GOT. Default offset is 0x7ff0.
254 // See "Global Data Symbols" in Chapter 6 in the following document:
255 // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
256 ElfSym::mipsGp = addAbsolute("_gp");
257
258 // On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
259 // start of function and 'gp' pointer into GOT.
260 if (symtab->find("_gp_disp"))
261 ElfSym::mipsGpDisp = addAbsolute("_gp_disp");
262
263 // The __gnu_local_gp is a magic symbol equal to the current value of 'gp'
264 // pointer. This symbol is used in the code generated by .cpload pseudo-op
265 // in case of using -mno-shared option.
266 // https://sourceware.org/ml/binutils/2004-12/msg00094.html
267 if (symtab->find("__gnu_local_gp"))
268 ElfSym::mipsLocalGp = addAbsolute("__gnu_local_gp");
269 } else if (config->emachine == EM_PPC) {
270 // glibc *crt1.o has a undefined reference to _SDA_BASE_. Since we don't
271 // support Small Data Area, define it arbitrarily as 0.
272 addOptionalRegular("_SDA_BASE_", nullptr, 0, STV_HIDDEN);
273 } else if (config->emachine == EM_PPC64) {
274 addPPC64SaveRestore();
275 }
276
277 // The Power Architecture 64-bit v2 ABI defines a TableOfContents (TOC) which
278 // combines the typical ELF GOT with the small data sections. It commonly
279 // includes .got .toc .sdata .sbss. The .TOC. symbol replaces both
280 // _GLOBAL_OFFSET_TABLE_ and _SDA_BASE_ from the 32-bit ABI. It is used to
281 // represent the TOC base which is offset by 0x8000 bytes from the start of
282 // the .got section.
283 // We do not allow _GLOBAL_OFFSET_TABLE_ to be defined by input objects as the
284 // correctness of some relocations depends on its value.
285 StringRef gotSymName =
286 (config->emachine == EM_PPC64) ? ".TOC." : "_GLOBAL_OFFSET_TABLE_";
287
288 if (Symbol *s = symtab->find(gotSymName)) {
289 if (s->isDefined()) {
290 error(toString(s->file) + " cannot redefine linker defined symbol '" +
291 gotSymName + "'");
292 return;
293 }
294
295 uint64_t gotOff = 0;
296 if (config->emachine == EM_PPC64)
297 gotOff = 0x8000;
298
299 s->resolve(Defined{/*file=*/nullptr, gotSymName, STB_GLOBAL, STV_HIDDEN,
300 STT_NOTYPE, gotOff, /*size=*/0, Out::elfHeader});
301 ElfSym::globalOffsetTable = cast<Defined>(s);
302 }
303
304 // __ehdr_start is the location of ELF file headers. Note that we define
305 // this symbol unconditionally even when using a linker script, which
306 // differs from the behavior implemented by GNU linker which only define
307 // this symbol if ELF headers are in the memory mapped segment.
308 addOptionalRegular("__ehdr_start", Out::elfHeader, 0, STV_HIDDEN);
309
310 // __executable_start is not documented, but the expectation of at
311 // least the Android libc is that it points to the ELF header.
312 addOptionalRegular("__executable_start", Out::elfHeader, 0, STV_HIDDEN);
313
314 // __dso_handle symbol is passed to cxa_finalize as a marker to identify
315 // each DSO. The address of the symbol doesn't matter as long as they are
316 // different in different DSOs, so we chose the start address of the DSO.
317 addOptionalRegular("__dso_handle", Out::elfHeader, 0, STV_HIDDEN);
318
319 // If linker script do layout we do not need to create any standard symbols.
320 if (script->hasSectionsCommand)
321 return;
322
323 auto add = [](StringRef s, int64_t pos) {
324 return addOptionalRegular(s, Out::elfHeader, pos, STV_DEFAULT);
325 };
326
327 ElfSym::bss = add("__bss_start", 0);
328 ElfSym::data = add("__data_start", 0);
329 ElfSym::end1 = add("end", -1);
330 ElfSym::end2 = add("_end", -1);
331 ElfSym::etext1 = add("etext", -1);
332 ElfSym::etext2 = add("_etext", -1);
333 ElfSym::edata1 = add("edata", -1);
334 ElfSym::edata2 = add("_edata", -1);
335}
336
337static OutputSection *findSection(StringRef name, unsigned partition = 1) {
338 for (BaseCommand *base : script->sectionCommands)
339 if (auto *sec = dyn_cast<OutputSection>(base))
340 if (sec->name == name && sec->partition == partition)
341 return sec;
342 return nullptr;
343}
344
345template <class ELFT> void elf::createSyntheticSections() {
346 // Initialize all pointers with NULL. This is needed because
347 // you can call lld::elf::main more than once as a library.
348 memset(&Out::first, 0, sizeof(Out));
349
350 // Add the .interp section first because it is not a SyntheticSection.
351 // The removeUnusedSyntheticSections() function relies on the
352 // SyntheticSections coming last.
353 if (needsInterpSection()) {
354 for (size_t i = 1; i <= partitions.size(); ++i) {
355 InputSection *sec = createInterpSection();
356 sec->partition = i;
357 inputSections.push_back(sec);
358 }
359 }
360
361 auto add = [](SyntheticSection *sec) { inputSections.push_back(sec); };
362
363 in.shStrTab = make<StringTableSection>(".shstrtab", false);
364
365 Out::programHeaders = make<OutputSection>("", 0, SHF_ALLOC);
366 Out::programHeaders->alignment = config->wordsize;
367
368 if (config->strip != StripPolicy::All) {
369 in.strTab = make<StringTableSection>(".strtab", false);
370 in.symTab = make<SymbolTableSection<ELFT>>(*in.strTab);
371 in.symTabShndx = make<SymtabShndxSection>();
372 }
373
374 in.bss = make<BssSection>(".bss", 0, 1);
375 add(in.bss);
376
377 // If there is a SECTIONS command and a .data.rel.ro section name use name
378 // .data.rel.ro.bss so that we match in the .data.rel.ro output section.
379 // This makes sure our relro is contiguous.
380 bool hasDataRelRo =
381 script->hasSectionsCommand && findSection(".data.rel.ro", 0);
382 in.bssRelRo =
383 make<BssSection>(hasDataRelRo ? ".data.rel.ro.bss" : ".bss.rel.ro", 0, 1);
384 add(in.bssRelRo);
385
386 // Add MIPS-specific sections.
387 if (config->emachine == EM_MIPS) {
388 if (!config->shared && config->hasDynSymTab) {
389 in.mipsRldMap = make<MipsRldMapSection>();
390 add(in.mipsRldMap);
391 }
392 if (auto *sec = MipsAbiFlagsSection<ELFT>::create())
393 add(sec);
394 if (auto *sec = MipsOptionsSection<ELFT>::create())
395 add(sec);
396 if (auto *sec = MipsReginfoSection<ELFT>::create())
397 add(sec);
398 }
399
400 StringRef relaDynName = config->isRela ? ".rela.dyn" : ".rel.dyn";
401
402 for (Partition &part : partitions) {
403 auto add = [&](SyntheticSection *sec) {
404 sec->partition = part.getNumber();
405 inputSections.push_back(sec);
406 };
407
408 if (!part.name.empty()) {
409 part.elfHeader = make<PartitionElfHeaderSection<ELFT>>();
410 part.elfHeader->name = part.name;
411 add(part.elfHeader);
412
413 part.programHeaders = make<PartitionProgramHeadersSection<ELFT>>();
414 add(part.programHeaders);
415 }
416
417 if (config->buildId != BuildIdKind::None) {
418 part.buildId = make<BuildIdSection>();
419 add(part.buildId);
420 }
421
422 part.dynStrTab = make<StringTableSection>(".dynstr", true);
423 part.dynSymTab = make<SymbolTableSection<ELFT>>(*part.dynStrTab);
424 part.dynamic = make<DynamicSection<ELFT>>();
425 if (config->androidPackDynRelocs)
426 part.relaDyn = make<AndroidPackedRelocationSection<ELFT>>(relaDynName);
427 else
428 part.relaDyn =
429 make<RelocationSection<ELFT>>(relaDynName, config->zCombreloc);
430
431 if (config->hasDynSymTab) {
432 part.dynSymTab = make<SymbolTableSection<ELFT>>(*part.dynStrTab);
433 add(part.dynSymTab);
434
435 part.verSym = make<VersionTableSection>();
436 add(part.verSym);
437
438 if (!namedVersionDefs().empty()) {
439 part.verDef = make<VersionDefinitionSection>();
440 add(part.verDef);
441 }
442
443 part.verNeed = make<VersionNeedSection<ELFT>>();
444 add(part.verNeed);
445
446 if (config->gnuHash) {
447 part.gnuHashTab = make<GnuHashTableSection>();
448 add(part.gnuHashTab);
449 }
450
451 if (config->sysvHash) {
452 part.hashTab = make<HashTableSection>();
453 add(part.hashTab);
454 }
455
456 add(part.dynamic);
457 add(part.dynStrTab);
458 add(part.relaDyn);
459 }
460
461 if (config->relrPackDynRelocs) {
462 part.relrDyn = make<RelrSection<ELFT>>();
463 add(part.relrDyn);
464 }
465
466 if (!config->relocatable) {
467 if (config->ehFrameHdr) {
468 part.ehFrameHdr = make<EhFrameHeader>();
469 add(part.ehFrameHdr);
470 }
471 part.ehFrame = make<EhFrameSection>();
472 add(part.ehFrame);
473 }
474
475 if (config->emachine == EM_ARM && !config->relocatable) {
476 // The ARMExidxsyntheticsection replaces all the individual .ARM.exidx
477 // InputSections.
478 part.armExidx = make<ARMExidxSyntheticSection>();
479 add(part.armExidx);
480 }
481 }
482
483 if (partitions.size() != 1) {
484 // Create the partition end marker. This needs to be in partition number 255
485 // so that it is sorted after all other partitions. It also has other
486 // special handling (see createPhdrs() and combineEhSections()).
487 in.partEnd = make<BssSection>(".part.end", config->maxPageSize, 1);
488 in.partEnd->partition = 255;
489 add(in.partEnd);
490
491 in.partIndex = make<PartitionIndexSection>();
492 addOptionalRegular("__part_index_begin", in.partIndex, 0);
493 addOptionalRegular("__part_index_end", in.partIndex,
494 in.partIndex->getSize());
495 add(in.partIndex);
496 }
497
498 // Add .got. MIPS' .got is so different from the other archs,
499 // it has its own class.
500 if (config->emachine == EM_MIPS) {
501 in.mipsGot = make<MipsGotSection>();
502 add(in.mipsGot);
503 } else {
504 in.got = make<GotSection>();
505 add(in.got);
506 }
507
508 if (config->emachine == EM_PPC) {
509 in.ppc32Got2 = make<PPC32Got2Section>();
510 add(in.ppc32Got2);
511 }
512
513 if (config->emachine == EM_PPC64) {
514 in.ppc64LongBranchTarget = make<PPC64LongBranchTargetSection>();
515 add(in.ppc64LongBranchTarget);
516 }
517
518 in.gotPlt = make<GotPltSection>();
519 add(in.gotPlt);
520 in.igotPlt = make<IgotPltSection>();
521 add(in.igotPlt);
522
523 // _GLOBAL_OFFSET_TABLE_ is defined relative to either .got.plt or .got. Treat
524 // it as a relocation and ensure the referenced section is created.
525 if (ElfSym::globalOffsetTable && config->emachine != EM_MIPS) {
526 if (target->gotBaseSymInGotPlt)
527 in.gotPlt->hasGotPltOffRel = true;
528 else
529 in.got->hasGotOffRel = true;
530 }
531
532 if (config->gdbIndex)
533 add(GdbIndexSection::create<ELFT>());
534
535 // We always need to add rel[a].plt to output if it has entries.
536 // Even for static linking it can contain R_[*]_IRELATIVE relocations.
537 in.relaPlt = make<RelocationSection<ELFT>>(
538 config->isRela ? ".rela.plt" : ".rel.plt", /*sort=*/false);
539 add(in.relaPlt);
540
541 // The relaIplt immediately follows .rel[a].dyn to ensure that the IRelative
542 // relocations are processed last by the dynamic loader. We cannot place the
543 // iplt section in .rel.dyn when Android relocation packing is enabled because
544 // that would cause a section type mismatch. However, because the Android
545 // dynamic loader reads .rel.plt after .rel.dyn, we can get the desired
546 // behaviour by placing the iplt section in .rel.plt.
547 in.relaIplt = make<RelocationSection<ELFT>>(
548 config->androidPackDynRelocs ? in.relaPlt->name : relaDynName,
549 /*sort=*/false);
550 add(in.relaIplt);
551
552 if ((config->emachine == EM_386 || config->emachine == EM_X86_64) &&
553 (config->andFeatures & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
554 in.ibtPlt = make<IBTPltSection>();
555 add(in.ibtPlt);
556 }
557
558 in.plt = config->emachine == EM_PPC ? make<PPC32GlinkSection>()
559 : make<PltSection>();
560 add(in.plt);
561 in.iplt = make<IpltSection>();
562 add(in.iplt);
563
564 if (config->andFeatures)
565 add(make<GnuPropertySection>());
566
567 // .note.GNU-stack is always added when we are creating a re-linkable
568 // object file. Other linkers are using the presence of this marker
569 // section to control the executable-ness of the stack area, but that
570 // is irrelevant these days. Stack area should always be non-executable
571 // by default. So we emit this section unconditionally.
572 if (config->relocatable)
573 add(make<GnuStackSection>());
574
575 if (in.symTab)
576 add(in.symTab);
577 if (in.symTabShndx)
578 add(in.symTabShndx);
579 add(in.shStrTab);
580 if (in.strTab)
581 add(in.strTab);
582}
583
584// The main function of the writer.
585template <class ELFT> void Writer<ELFT>::run() {
586 copyLocalSymbols();
587
588 if (config->copyRelocs)
589 addSectionSymbols();
590
591 // Now that we have a complete set of output sections. This function
592 // completes section contents. For example, we need to add strings
593 // to the string table, and add entries to .got and .plt.
594 // finalizeSections does that.
595 finalizeSections();
596 checkExecuteOnly();
597 if (errorCount())
598 return;
599
600 // If -compressed-debug-sections is specified, we need to compress
601 // .debug_* sections. Do it right now because it changes the size of
602 // output sections.
603 for (OutputSection *sec : outputSections)
604 sec->maybeCompress<ELFT>();
605
606 if (script->hasSectionsCommand)
607 script->allocateHeaders(mainPart->phdrs);
608
609 // Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
610 // 0 sized region. This has to be done late since only after assignAddresses
611 // we know the size of the sections.
612 for (Partition &part : partitions)
613 removeEmptyPTLoad(part.phdrs);
614
615 if (!config->oFormatBinary)
616 assignFileOffsets();
617 else
618 assignFileOffsetsBinary();
619
620 for (Partition &part : partitions)
621 setPhdrs(part);
622
623 if (config->relocatable)
624 for (OutputSection *sec : outputSections)
625 sec->addr = 0;
626
627 // Handle --print-map(-M)/--Map, --cref and --print-archive-stats=. Dump them
628 // before checkSections() because the files may be useful in case
629 // checkSections() or openFile() fails, for example, due to an erroneous file
630 // size.
631 writeMapFile();
632 writeCrossReferenceTable();
633 writeArchiveStats();
634
635 if (config->checkSections)
636 checkSections();
637
638 // It does not make sense try to open the file if we have error already.
639 if (errorCount())
640 return;
641
642 {
643 llvm::TimeTraceScope timeScope("Write output file");
644 // Write the result down to a file.
645 openFile();
646 if (errorCount())
647 return;
648
649 if (!config->oFormatBinary) {
650 if (config->zSeparate != SeparateSegmentKind::None)
651 writeTrapInstr();
652 writeHeader();
653 writeSections();
654 } else {
655 writeSectionsBinary();
656 }
657
658 // Backfill .note.gnu.build-id section content. This is done at last
659 // because the content is usually a hash value of the entire output file.
660 writeBuildId();
661 if (errorCount())
662 return;
663
664 if (auto e = buffer->commit())
665 error("failed to write to the output file: " + toString(std::move(e)));
666 }
667}
668
669template <class ELFT, class RelTy>
670static void markUsedLocalSymbolsImpl(ObjFile<ELFT> *file,
671 llvm::ArrayRef<RelTy> rels) {
672 for (const RelTy &rel : rels) {
673 Symbol &sym = file->getRelocTargetSym(rel);
674 if (sym.isLocal())
675 sym.used = true;
676 }
677}
678
679// The function ensures that the "used" field of local symbols reflects the fact
680// that the symbol is used in a relocation from a live section.
681template <class ELFT> static void markUsedLocalSymbols() {
682 // With --gc-sections, the field is already filled.
683 // See MarkLive<ELFT>::resolveReloc().
684 if (config->gcSections)
685 return;
686 // Without --gc-sections, the field is initialized with "true".
687 // Drop the flag first and then rise for symbols referenced in relocations.
688 for (InputFile *file : objectFiles) {
689 ObjFile<ELFT> *f = cast<ObjFile<ELFT>>(file);
690 for (Symbol *b : f->getLocalSymbols())
691 b->used = false;
692 for (InputSectionBase *s : f->getSections()) {
693 InputSection *isec = dyn_cast_or_null<InputSection>(s);
694 if (!isec)
695 continue;
696 if (isec->type == SHT_REL)
697 markUsedLocalSymbolsImpl(f, isec->getDataAs<typename ELFT::Rel>());
698 else if (isec->type == SHT_RELA)
699 markUsedLocalSymbolsImpl(f, isec->getDataAs<typename ELFT::Rela>());
700 }
701 }
702}
703
704static bool shouldKeepInSymtab(const Defined &sym) {
705 if (sym.isSection())
706 return false;
707
708 // If --emit-reloc or -r is given, preserve symbols referenced by relocations
709 // from live sections.
710 if (config->copyRelocs && sym.used)
711 return true;
712
713 // Exclude local symbols pointing to .ARM.exidx sections.
714 // They are probably mapping symbols "$d", which are optional for these
715 // sections. After merging the .ARM.exidx sections, some of these symbols
716 // may become dangling. The easiest way to avoid the issue is not to add
717 // them to the symbol table from the beginning.
718 if (config->emachine == EM_ARM && sym.section &&
719 sym.section->type == SHT_ARM_EXIDX)
720 return false;
721
722 if (config->discard == DiscardPolicy::None)
723 return true;
724 if (config->discard == DiscardPolicy::All)
725 return false;
726
727 // In ELF assembly .L symbols are normally discarded by the assembler.
728 // If the assembler fails to do so, the linker discards them if
729 // * --discard-locals is used.
730 // * The symbol is in a SHF_MERGE section, which is normally the reason for
731 // the assembler keeping the .L symbol.
732 StringRef name = sym.getName();
733 bool isLocal = name.startswith(".L") || name.empty();
734 if (!isLocal)
735 return true;
736
737 if (config->discard == DiscardPolicy::Locals)
738 return false;
739
740 SectionBase *sec = sym.section;
741 return !sec || !(sec->flags & SHF_MERGE);
742}
743
744static bool includeInSymtab(const Symbol &b) {
745 if (!b.isLocal() && !b.isUsedInRegularObj)
746 return false;
747
748 if (auto *d = dyn_cast<Defined>(&b)) {
749 // Always include absolute symbols.
750 SectionBase *sec = d->section;
751 if (!sec)
752 return true;
753 sec = sec->repl;
754
755 // Exclude symbols pointing to garbage-collected sections.
756 if (isa<InputSectionBase>(sec) && !sec->isLive())
757 return false;
758
759 if (auto *s = dyn_cast<MergeInputSection>(sec))
760 if (!s->getSectionPiece(d->value)->live)
761 return false;
762 return true;
763 }
764 return b.used;
765}
766
767// Local symbols are not in the linker's symbol table. This function scans
768// each object file's symbol table to copy local symbols to the output.
769template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
770 if (!in.symTab)
771 return;
772 llvm::TimeTraceScope timeScope("Add local symbols");
773 if (config->copyRelocs && config->discard != DiscardPolicy::None)
774 markUsedLocalSymbols<ELFT>();
775 for (InputFile *file : objectFiles) {
776 ObjFile<ELFT> *f = cast<ObjFile<ELFT>>(file);
777 for (Symbol *b : f->getLocalSymbols()) {
778 assert(b->isLocal() && "should have been caught in initializeSymbols()")((void)0);
779 auto *dr = dyn_cast<Defined>(b);
780
781 // No reason to keep local undefined symbol in symtab.
782 if (!dr)
783 continue;
784 if (!includeInSymtab(*b))
785 continue;
786 if (!shouldKeepInSymtab(*dr))
787 continue;
788 in.symTab->addSymbol(b);
789 }
790 }
791}
792
793// Create a section symbol for each output section so that we can represent
794// relocations that point to the section. If we know that no relocation is
795// referring to a section (that happens if the section is a synthetic one), we
796// don't create a section symbol for that section.
797template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
798 for (BaseCommand *base : script->sectionCommands) {
799 auto *sec = dyn_cast<OutputSection>(base);
800 if (!sec)
801 continue;
802 auto i = llvm::find_if(sec->sectionCommands, [](BaseCommand *base) {
803 if (auto *isd = dyn_cast<InputSectionDescription>(base))
804 return !isd->sections.empty();
805 return false;
806 });
807 if (i == sec->sectionCommands.end())
808 continue;
809 InputSectionBase *isec = cast<InputSectionDescription>(*i)->sections[0];
810
811 // Relocations are not using REL[A] section symbols.
812 if (isec->type == SHT_REL || isec->type == SHT_RELA)
813 continue;
814
815 // Unlike other synthetic sections, mergeable output sections contain data
816 // copied from input sections, and there may be a relocation pointing to its
817 // contents if -r or -emit-reloc are given.
818 if (isa<SyntheticSection>(isec) && !(isec->flags & SHF_MERGE))
819 continue;
820
821 // Set the symbol to be relative to the output section so that its st_value
822 // equals the output section address. Note, there may be a gap between the
823 // start of the output section and isec.
824 auto *sym =
825 make<Defined>(isec->file, "", STB_LOCAL, /*stOther=*/0, STT_SECTION,
826 /*value=*/0, /*size=*/0, isec->getOutputSection());
827 in.symTab->addSymbol(sym);
828 }
829}
830
831// Today's loaders have a feature to make segments read-only after
832// processing dynamic relocations to enhance security. PT_GNU_RELRO
833// is defined for that.
834//
835// This function returns true if a section needs to be put into a
836// PT_GNU_RELRO segment.
837static bool isRelroSection(const OutputSection *sec) {
838 if (!config->zRelro)
839 return false;
840
841 uint64_t flags = sec->flags;
842
843 // Non-allocatable or non-writable sections don't need RELRO because
844 // they are not writable or not even mapped to memory in the first place.
845 // RELRO is for sections that are essentially read-only but need to
846 // be writable only at process startup to allow dynamic linker to
847 // apply relocations.
848 if (!(flags & SHF_ALLOC) || !(flags & SHF_WRITE))
849 return false;
850
851 // Once initialized, TLS data segments are used as data templates
852 // for a thread-local storage. For each new thread, runtime
853 // allocates memory for a TLS and copy templates there. No thread
854 // are supposed to use templates directly. Thus, it can be in RELRO.
855 if (flags & SHF_TLS)
856 return true;
857
858 // .init_array, .preinit_array and .fini_array contain pointers to
859 // functions that are executed on process startup or exit. These
860 // pointers are set by the static linker, and they are not expected
861 // to change at runtime. But if you are an attacker, you could do
862 // interesting things by manipulating pointers in .fini_array, for
863 // example. So they are put into RELRO.
864 uint32_t type = sec->type;
865 if (type == SHT_INIT_ARRAY || type == SHT_FINI_ARRAY ||
866 type == SHT_PREINIT_ARRAY)
867 return true;
868
869 // .got contains pointers to external symbols. They are resolved by
870 // the dynamic linker when a module is loaded into memory, and after
871 // that they are not expected to change. So, it can be in RELRO.
872 if (in.got && sec == in.got->getParent())
873 return true;
874
875 // .toc is a GOT-ish section for PowerPC64. Their contents are accessed
876 // through r2 register, which is reserved for that purpose. Since r2 is used
877 // for accessing .got as well, .got and .toc need to be close enough in the
878 // virtual address space. Usually, .toc comes just after .got. Since we place
879 // .got into RELRO, .toc needs to be placed into RELRO too.
880 if (sec->name.equals(".toc"))
881 return true;
882
883 // .got.plt contains pointers to external function symbols. They are
884 // by default resolved lazily, so we usually cannot put it into RELRO.
885 // However, if "-z now" is given, the lazy symbol resolution is
886 // disabled, which enables us to put it into RELRO.
887 if (sec == in.gotPlt->getParent())
888#ifndef __OpenBSD__1
889 return config->zNow;
890#else
891 return true; /* kbind(2) means we can always put these in RELRO */
892#endif
893
894 // .dynamic section contains data for the dynamic linker, and
895 // there's no need to write to it at runtime, so it's better to put
896 // it into RELRO.
897 if (sec->name == ".dynamic")
898 return true;
899
900 // Sections with some special names are put into RELRO. This is a
901 // bit unfortunate because section names shouldn't be significant in
902 // ELF in spirit. But in reality many linker features depend on
903 // magic section names.
904 StringRef s = sec->name;
905 return s == ".data.rel.ro" || s == ".bss.rel.ro" || s == ".ctors" ||
906 s == ".dtors" || s == ".jcr" || s == ".eh_frame" ||
907 s == ".fini_array" || s == ".init_array" ||
908 s == ".openbsd.randomdata" || s == ".preinit_array";
909}
910
911// We compute a rank for each section. The rank indicates where the
912// section should be placed in the file. Instead of using simple
913// numbers (0,1,2...), we use a series of flags. One for each decision
914// point when placing the section.
915// Using flags has two key properties:
916// * It is easy to check if a give branch was taken.
917// * It is easy two see how similar two ranks are (see getRankProximity).
918enum RankFlags {
919 RF_NOT_ADDR_SET = 1 << 27,
920 RF_NOT_ALLOC = 1 << 26,
921 RF_PARTITION = 1 << 18, // Partition number (8 bits)
922 RF_NOT_PART_EHDR = 1 << 17,
923 RF_NOT_PART_PHDR = 1 << 16,
924 RF_NOT_INTERP = 1 << 15,
925 RF_NOT_NOTE = 1 << 14,
926 RF_WRITE = 1 << 13,
927 RF_EXEC_WRITE = 1 << 12,
928 RF_EXEC = 1 << 11,
929 RF_RODATA = 1 << 10,
930 RF_NOT_RELRO = 1 << 9,
931 RF_NOT_TLS = 1 << 8,
932 RF_BSS = 1 << 7,
933 RF_PPC_NOT_TOCBSS = 1 << 6,
934 RF_PPC_TOCL = 1 << 5,
935 RF_PPC_TOC = 1 << 4,
936 RF_PPC_GOT = 1 << 3,
937 RF_PPC_BRANCH_LT = 1 << 2,
938 RF_MIPS_GPREL = 1 << 1,
939 RF_MIPS_NOT_GOT = 1 << 0
940};
941
942static unsigned getSectionRank(const OutputSection *sec) {
943 unsigned rank = sec->partition * RF_PARTITION;
944
945 // We want to put section specified by -T option first, so we
946 // can start assigning VA starting from them later.
947 if (config->sectionStartMap.count(sec->name))
948 return rank;
949 rank |= RF_NOT_ADDR_SET;
950
951 // Allocatable sections go first to reduce the total PT_LOAD size and
952 // so debug info doesn't change addresses in actual code.
953 if (!(sec->flags & SHF_ALLOC))
954 return rank | RF_NOT_ALLOC;
955
956 if (sec->type == SHT_LLVM_PART_EHDR)
957 return rank;
958 rank |= RF_NOT_PART_EHDR;
959
960 if (sec->type == SHT_LLVM_PART_PHDR)
961 return rank;
962 rank |= RF_NOT_PART_PHDR;
963
964 // Put .interp first because some loaders want to see that section
965 // on the first page of the executable file when loaded into memory.
966 if (sec->name == ".interp")
967 return rank;
968 rank |= RF_NOT_INTERP;
969
970 // Put .note sections (which make up one PT_NOTE) at the beginning so that
971 // they are likely to be included in a core file even if core file size is
972 // limited. In particular, we want a .note.gnu.build-id and a .note.tag to be
973 // included in a core to match core files with executables.
974 if (sec->type == SHT_NOTE)
975 return rank;
976 rank |= RF_NOT_NOTE;
977
978 // Sort sections based on their access permission in the following
979 // order: R, RX, RWX, RW. This order is based on the following
980 // considerations:
981 // * Read-only sections come first such that they go in the
982 // PT_LOAD covering the program headers at the start of the file.
983 // * Read-only, executable sections come next.
984 // * Writable, executable sections follow such that .plt on
985 // architectures where it needs to be writable will be placed
986 // between .text and .data.
987 // * Writable sections come last, such that .bss lands at the very
988 // end of the last PT_LOAD.
989 bool isExec = sec->flags & SHF_EXECINSTR;
990 bool isWrite = sec->flags & SHF_WRITE;
991
992 if (isExec) {
993 if (isWrite)
994 rank |= RF_EXEC_WRITE;
995 else
996 rank |= RF_EXEC;
997 } else if (isWrite) {
998 rank |= RF_WRITE;
999 } else if (sec->type == SHT_PROGBITS) {
1000 // Make non-executable and non-writable PROGBITS sections (e.g .rodata
1001 // .eh_frame) closer to .text. They likely contain PC or GOT relative
1002 // relocations and there could be relocation overflow if other huge sections
1003 // (.dynstr .dynsym) were placed in between.
1004 rank |= RF_RODATA;
1005 }
1006
1007 // Place RelRo sections first. After considering SHT_NOBITS below, the
1008 // ordering is PT_LOAD(PT_GNU_RELRO(.data.rel.ro .bss.rel.ro) | .data .bss),
1009 // where | marks where page alignment happens. An alternative ordering is
1010 // PT_LOAD(.data | PT_GNU_RELRO( .data.rel.ro .bss.rel.ro) | .bss), but it may
1011 // waste more bytes due to 2 alignment places.
1012 if (!isRelroSection(sec))
1013 rank |= RF_NOT_RELRO;
1014
1015 // If we got here we know that both A and B are in the same PT_LOAD.
1016
1017 // The TLS initialization block needs to be a single contiguous block in a R/W
1018 // PT_LOAD, so stick TLS sections directly before the other RelRo R/W
1019 // sections. Since p_filesz can be less than p_memsz, place NOBITS sections
1020 // after PROGBITS.
1021 if (!(sec->flags & SHF_TLS))
1022 rank |= RF_NOT_TLS;
1023
1024 // Within TLS sections, or within other RelRo sections, or within non-RelRo
1025 // sections, place non-NOBITS sections first.
1026 if (sec->type == SHT_NOBITS)
1027 rank |= RF_BSS;
1028
1029 // Some architectures have additional ordering restrictions for sections
1030 // within the same PT_LOAD.
1031 if (config->emachine == EM_PPC64) {
1032 // PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections
1033 // that we would like to make sure appear is a specific order to maximize
1034 // their coverage by a single signed 16-bit offset from the TOC base
1035 // pointer. Conversely, the special .tocbss section should be first among
1036 // all SHT_NOBITS sections. This will put it next to the loaded special
1037 // PPC64 sections (and, thus, within reach of the TOC base pointer).
1038 StringRef name = sec->name;
1039 if (name != ".tocbss")
1040 rank |= RF_PPC_NOT_TOCBSS;
1041
1042 if (name == ".toc1")
1043 rank |= RF_PPC_TOCL;
1044
1045 if (name == ".toc")
1046 rank |= RF_PPC_TOC;
1047
1048 if (name == ".got")
1049 rank |= RF_PPC_GOT;
1050
1051 if (name == ".branch_lt")
1052 rank |= RF_PPC_BRANCH_LT;
1053 }
1054
1055 if (config->emachine == EM_MIPS) {
1056 // All sections with SHF_MIPS_GPREL flag should be grouped together
1057 // because data in these sections is addressable with a gp relative address.
1058 if (sec->flags & SHF_MIPS_GPREL)
1059 rank |= RF_MIPS_GPREL;
1060
1061 if (sec->name != ".got")
1062 rank |= RF_MIPS_NOT_GOT;
1063 }
1064
1065 return rank;
1066}
1067
1068static bool compareSections(const BaseCommand *aCmd, const BaseCommand *bCmd) {
1069 const OutputSection *a = cast<OutputSection>(aCmd);
1070 const OutputSection *b = cast<OutputSection>(bCmd);
1071
1072 if (a->sortRank != b->sortRank)
1073 return a->sortRank < b->sortRank;
1074
1075 if (!(a->sortRank & RF_NOT_ADDR_SET))
1076 return config->sectionStartMap.lookup(a->name) <
1077 config->sectionStartMap.lookup(b->name);
1078 return false;
1079}
1080
1081void PhdrEntry::add(OutputSection *sec) {
1082 lastSec = sec;
1083 if (!firstSec)
1084 firstSec = sec;
1085 p_align = std::max(p_align, sec->alignment);
1086 if (p_type == PT_LOAD)
1087 sec->ptLoad = this;
1088}
1089
1090// The beginning and the ending of .rel[a].plt section are marked
1091// with __rel[a]_iplt_{start,end} symbols if it is a statically linked
1092// executable. The runtime needs these symbols in order to resolve
1093// all IRELATIVE relocs on startup. For dynamic executables, we don't
1094// need these symbols, since IRELATIVE relocs are resolved through GOT
1095// and PLT. For details, see http://www.airs.com/blog/archives/403.
1096template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
1097 if (config->relocatable || config->isPic)
1098 return;
1099
1100 // By default, __rela_iplt_{start,end} belong to a dummy section 0
1101 // because .rela.plt might be empty and thus removed from output.
1102 // We'll override Out::elfHeader with In.relaIplt later when we are
1103 // sure that .rela.plt exists in output.
1104 ElfSym::relaIpltStart = addOptionalRegular(
1105 config->isRela ? "__rela_iplt_start" : "__rel_iplt_start",
1106 Out::elfHeader, 0, STV_HIDDEN, STB_WEAK);
1107
1108 ElfSym::relaIpltEnd = addOptionalRegular(
1109 config->isRela ? "__rela_iplt_end" : "__rel_iplt_end",
1110 Out::elfHeader, 0, STV_HIDDEN, STB_WEAK);
1111}
1112
1113template <class ELFT>
1114void Writer<ELFT>::forEachRelSec(
1115 llvm::function_ref<void(InputSectionBase &)> fn) {
1116 // Scan all relocations. Each relocation goes through a series
1117 // of tests to determine if it needs special treatment, such as
1118 // creating GOT, PLT, copy relocations, etc.
1119 // Note that relocations for non-alloc sections are directly
1120 // processed by InputSection::relocateNonAlloc.
1121 for (InputSectionBase *isec : inputSections)
1122 if (isec->isLive() && isa<InputSection>(isec) && (isec->flags & SHF_ALLOC))
1123 fn(*isec);
1124 for (Partition &part : partitions) {
1125 for (EhInputSection *es : part.ehFrame->sections)
1126 fn(*es);
1127 if (part.armExidx && part.armExidx->isLive())
1128 for (InputSection *ex : part.armExidx->exidxSections)
1129 fn(*ex);
1130 }
1131}
1132
1133// This function generates assignments for predefined symbols (e.g. _end or
1134// _etext) and inserts them into the commands sequence to be processed at the
1135// appropriate time. This ensures that the value is going to be correct by the
1136// time any references to these symbols are processed and is equivalent to
1137// defining these symbols explicitly in the linker script.
1138template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() {
1139 if (ElfSym::globalOffsetTable) {
1140 // The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention usually
1141 // to the start of the .got or .got.plt section.
1142 InputSection *gotSection = in.gotPlt;
1143 if (!target->gotBaseSymInGotPlt)
1144 gotSection = in.mipsGot ? cast<InputSection>(in.mipsGot)
1145 : cast<InputSection>(in.got);
1146 ElfSym::globalOffsetTable->section = gotSection;
1147 }
1148
1149 // .rela_iplt_{start,end} mark the start and the end of in.relaIplt.
1150 if (ElfSym::relaIpltStart && in.relaIplt->isNeeded()) {
1151 ElfSym::relaIpltStart->section = in.relaIplt;
1152 ElfSym::relaIpltEnd->section = in.relaIplt;
1153 ElfSym::relaIpltEnd->value = in.relaIplt->getSize();
1154 }
1155
1156 PhdrEntry *last = nullptr;
1157 PhdrEntry *lastRO = nullptr;
1158
1159 for (Partition &part : partitions) {
1160 for (PhdrEntry *p : part.phdrs) {
1161 if (p->p_type != PT_LOAD)
1162 continue;
1163 last = p;
1164 if (!(p->p_flags & PF_W))
1165 lastRO = p;
1166 }
1167 }
1168
1169 if (lastRO) {
1170 // _etext is the first location after the last read-only loadable segment.
1171 if (ElfSym::etext1)
1172 ElfSym::etext1->section = lastRO->lastSec;
1173 if (ElfSym::etext2)
1174 ElfSym::etext2->section = lastRO->lastSec;
1175 }
1176
1177 if (last) {
1178 // _edata points to the end of the last mapped initialized section.
1179 OutputSection *edata = nullptr;
1180 for (OutputSection *os : outputSections) {
1181 if (os->type != SHT_NOBITS)
1182 edata = os;
1183 if (os == last->lastSec)
1184 break;
1185 }
1186
1187 if (ElfSym::edata1)
1188 ElfSym::edata1->section = edata;
1189 if (ElfSym::edata2)
1190 ElfSym::edata2->section = edata;
1191
1192 // _end is the first location after the uninitialized data region.
1193 if (ElfSym::end1)
1194 ElfSym::end1->section = last->lastSec;
1195 if (ElfSym::end2)
1196 ElfSym::end2->section = last->lastSec;
1197 }
1198
1199 if (ElfSym::bss)
1200 ElfSym::bss->section = findSection(".bss");
1201
1202 if (ElfSym::data)
1203 ElfSym::data->section = findSection(".data");
1204
1205 // Setup MIPS _gp_disp/__gnu_local_gp symbols which should
1206 // be equal to the _gp symbol's value.
1207 if (ElfSym::mipsGp) {
1208 // Find GP-relative section with the lowest address
1209 // and use this address to calculate default _gp value.
1210 for (OutputSection *os : outputSections) {
1211 if (os->flags & SHF_MIPS_GPREL) {
1212 ElfSym::mipsGp->section = os;
1213 ElfSym::mipsGp->value = 0x7ff0;
1214 break;
1215 }
1216 }
1217 }
1218}
1219
1220// We want to find how similar two ranks are.
1221// The more branches in getSectionRank that match, the more similar they are.
1222// Since each branch corresponds to a bit flag, we can just use
1223// countLeadingZeros.
1224static int getRankProximityAux(OutputSection *a, OutputSection *b) {
1225 return countLeadingZeros(a->sortRank ^ b->sortRank);
1226}
1227
1228static int getRankProximity(OutputSection *a, BaseCommand *b) {
1229 auto *sec = dyn_cast<OutputSection>(b);
1230 return (sec && sec->hasInputSections) ? getRankProximityAux(a, sec) : -1;
1231}
1232
1233// When placing orphan sections, we want to place them after symbol assignments
1234// so that an orphan after
1235// begin_foo = .;
1236// foo : { *(foo) }
1237// end_foo = .;
1238// doesn't break the intended meaning of the begin/end symbols.
1239// We don't want to go over sections since findOrphanPos is the
1240// one in charge of deciding the order of the sections.
1241// We don't want to go over changes to '.', since doing so in
1242// rx_sec : { *(rx_sec) }
1243// . = ALIGN(0x1000);
1244// /* The RW PT_LOAD starts here*/
1245// rw_sec : { *(rw_sec) }
1246// would mean that the RW PT_LOAD would become unaligned.
1247static bool shouldSkip(BaseCommand *cmd) {
1248 if (auto *assign = dyn_cast<SymbolAssignment>(cmd))
1249 return assign->name != ".";
1250 return false;
1251}
1252
1253// We want to place orphan sections so that they share as much
1254// characteristics with their neighbors as possible. For example, if
1255// both are rw, or both are tls.
1256static std::vector<BaseCommand *>::iterator
1257findOrphanPos(std::vector<BaseCommand *>::iterator b,
1258 std::vector<BaseCommand *>::iterator e) {
1259 OutputSection *sec = cast<OutputSection>(*e);
1260
1261 // Find the first element that has as close a rank as possible.
1262 auto i = std::max_element(b, e, [=](BaseCommand *a, BaseCommand *b) {
1263 return getRankProximity(sec, a) < getRankProximity(sec, b);
1264 });
1265 if (i == e)
1266 return e;
1267
1268 // Consider all existing sections with the same proximity.
1269 int proximity = getRankProximity(sec, *i);
1270 for (; i != e; ++i) {
1271 auto *curSec = dyn_cast<OutputSection>(*i);
1272 if (!curSec || !curSec->hasInputSections)
1273 continue;
1274 if (getRankProximity(sec, curSec) != proximity ||
1275 sec->sortRank < curSec->sortRank)
1276 break;
1277 }
1278
1279 auto isOutputSecWithInputSections = [](BaseCommand *cmd) {
1280 auto *os = dyn_cast<OutputSection>(cmd);
1281 return os && os->hasInputSections;
1282 };
1283 auto j = std::find_if(llvm::make_reverse_iterator(i),
1284 llvm::make_reverse_iterator(b),
1285 isOutputSecWithInputSections);
1286 i = j.base();
1287
1288 // As a special case, if the orphan section is the last section, put
1289 // it at the very end, past any other commands.
1290 // This matches bfd's behavior and is convenient when the linker script fully
1291 // specifies the start of the file, but doesn't care about the end (the non
1292 // alloc sections for example).
1293 auto nextSec = std::find_if(i, e, isOutputSecWithInputSections);
1294 if (nextSec == e)
1295 return e;
1296
1297 while (i != e && shouldSkip(*i))
1298 ++i;
1299 return i;
1300}
1301
1302// Adds random priorities to sections not already in the map.
1303static void maybeShuffle(DenseMap<const InputSectionBase *, int> &order) {
1304 if (config->shuffleSections.empty())
1305 return;
1306
1307 std::vector<InputSectionBase *> matched, sections = inputSections;
1308 matched.reserve(sections.size());
1309 for (const auto &patAndSeed : config->shuffleSections) {
1310 matched.clear();
1311 for (InputSectionBase *sec : sections)
1312 if (patAndSeed.first.match(sec->name))
1313 matched.push_back(sec);
1314 const uint32_t seed = patAndSeed.second;
1315 if (seed == UINT32_MAX0xffffffffU) {
1316 // If --shuffle-sections <section-glob>=-1, reverse the section order. The
1317 // section order is stable even if the number of sections changes. This is
1318 // useful to catch issues like static initialization order fiasco
1319 // reliably.
1320 std::reverse(matched.begin(), matched.end());
1321 } else {
1322 std::mt19937 g(seed ? seed : std::random_device()());
1323 llvm::shuffle(matched.begin(), matched.end(), g);
1324 }
1325 size_t i = 0;
1326 for (InputSectionBase *&sec : sections)
1327 if (patAndSeed.first.match(sec->name))
1328 sec = matched[i++];
1329 }
1330
1331 // Existing priorities are < 0, so use priorities >= 0 for the missing
1332 // sections.
1333 int prio = 0;
1334 for (InputSectionBase *sec : sections) {
1335 if (order.try_emplace(sec, prio).second)
1336 ++prio;
1337 }
1338}
1339
1340// Builds section order for handling --symbol-ordering-file.
1341static DenseMap<const InputSectionBase *, int> buildSectionOrder() {
1342 DenseMap<const InputSectionBase *, int> sectionOrder;
1343 // Use the rarely used option -call-graph-ordering-file to sort sections.
1344 if (!config->callGraphProfile.empty())
1345 return computeCallGraphProfileOrder();
1346
1347 if (config->symbolOrderingFile.empty())
1348 return sectionOrder;
1349
1350 struct SymbolOrderEntry {
1351 int priority;
1352 bool present;
1353 };
1354
1355 // Build a map from symbols to their priorities. Symbols that didn't
1356 // appear in the symbol ordering file have the lowest priority 0.
1357 // All explicitly mentioned symbols have negative (higher) priorities.
1358 DenseMap<StringRef, SymbolOrderEntry> symbolOrder;
1359 int priority = -config->symbolOrderingFile.size();
1360 for (StringRef s : config->symbolOrderingFile)
1361 symbolOrder.insert({s, {priority++, false}});
1362
1363 // Build a map from sections to their priorities.
1364 auto addSym = [&](Symbol &sym) {
1365 auto it = symbolOrder.find(sym.getName());
1366 if (it == symbolOrder.end())
1367 return;
1368 SymbolOrderEntry &ent = it->second;
1369 ent.present = true;
1370
1371 maybeWarnUnorderableSymbol(&sym);
1372
1373 if (auto *d = dyn_cast<Defined>(&sym)) {
1374 if (auto *sec = dyn_cast_or_null<InputSectionBase>(d->section)) {
1375 int &priority = sectionOrder[cast<InputSectionBase>(sec->repl)];
1376 priority = std::min(priority, ent.priority);
1377 }
1378 }
1379 };
1380
1381 // We want both global and local symbols. We get the global ones from the
1382 // symbol table and iterate the object files for the local ones.
1383 for (Symbol *sym : symtab->symbols())
1384 if (!sym->isLazy())
1385 addSym(*sym);
1386
1387 for (InputFile *file : objectFiles)
1388 for (Symbol *sym : file->getSymbols()) {
1389 if (!sym->isLocal())
1390 break;
1391 addSym(*sym);
1392 }
1393
1394 if (config->warnSymbolOrdering)
1395 for (auto orderEntry : symbolOrder)
1396 if (!orderEntry.second.present)
1397 warn("symbol ordering file: no such symbol: " + orderEntry.first);
1398
1399 return sectionOrder;
1400}
1401
1402// Sorts the sections in ISD according to the provided section order.
1403static void
1404sortISDBySectionOrder(InputSectionDescription *isd,
1405 const DenseMap<const InputSectionBase *, int> &order) {
1406 std::vector<InputSection *> unorderedSections;
1407 std::vector<std::pair<InputSection *, int>> orderedSections;
1408 uint64_t unorderedSize = 0;
1409
1410 for (InputSection *isec : isd->sections) {
1411 auto i = order.find(isec);
1412 if (i == order.end()) {
1413 unorderedSections.push_back(isec);
1414 unorderedSize += isec->getSize();
1415 continue;
1416 }
1417 orderedSections.push_back({isec, i->second});
1418 }
1419 llvm::sort(orderedSections, llvm::less_second());
1420
1421 // Find an insertion point for the ordered section list in the unordered
1422 // section list. On targets with limited-range branches, this is the mid-point
1423 // of the unordered section list. This decreases the likelihood that a range
1424 // extension thunk will be needed to enter or exit the ordered region. If the
1425 // ordered section list is a list of hot functions, we can generally expect
1426 // the ordered functions to be called more often than the unordered functions,
1427 // making it more likely that any particular call will be within range, and
1428 // therefore reducing the number of thunks required.
1429 //
1430 // For example, imagine that you have 8MB of hot code and 32MB of cold code.
1431 // If the layout is:
1432 //
1433 // 8MB hot
1434 // 32MB cold
1435 //
1436 // only the first 8-16MB of the cold code (depending on which hot function it
1437 // is actually calling) can call the hot code without a range extension thunk.
1438 // However, if we use this layout:
1439 //
1440 // 16MB cold
1441 // 8MB hot
1442 // 16MB cold
1443 //
1444 // both the last 8-16MB of the first block of cold code and the first 8-16MB
1445 // of the second block of cold code can call the hot code without a thunk. So
1446 // we effectively double the amount of code that could potentially call into
1447 // the hot code without a thunk.
1448 size_t insPt = 0;
1449 if (target->getThunkSectionSpacing() && !orderedSections.empty()) {
1450 uint64_t unorderedPos = 0;
1451 for (; insPt != unorderedSections.size(); ++insPt) {
1452 unorderedPos += unorderedSections[insPt]->getSize();
1453 if (unorderedPos > unorderedSize / 2)
1454 break;
1455 }
1456 }
1457
1458 isd->sections.clear();
1459 for (InputSection *isec : makeArrayRef(unorderedSections).slice(0, insPt))
1460 isd->sections.push_back(isec);
1461 for (std::pair<InputSection *, int> p : orderedSections)
1462 isd->sections.push_back(p.first);
1463 for (InputSection *isec : makeArrayRef(unorderedSections).slice(insPt))
1464 isd->sections.push_back(isec);
1465}
1466
1467static void sortSection(OutputSection *sec,
1468 const DenseMap<const InputSectionBase *, int> &order) {
1469 StringRef name = sec->name;
1470
1471 // Never sort these.
1472 if (name == ".init" || name == ".fini")
1473 return;
1474
1475 // IRelative relocations that usually live in the .rel[a].dyn section should
1476 // be processed last by the dynamic loader. To achieve that we add synthetic
1477 // sections in the required order from the beginning so that the in.relaIplt
1478 // section is placed last in an output section. Here we just do not apply
1479 // sorting for an output section which holds the in.relaIplt section.
1480 if (in.relaIplt->getParent() == sec)
1481 return;
1482
1483 // Sort input sections by priority using the list provided by
1484 // --symbol-ordering-file or --shuffle-sections=. This is a least significant
1485 // digit radix sort. The sections may be sorted stably again by a more
1486 // significant key.
1487 if (!order.empty())
1488 for (BaseCommand *b : sec->sectionCommands)
1489 if (auto *isd = dyn_cast<InputSectionDescription>(b))
1490 sortISDBySectionOrder(isd, order);
1491
1492 // Sort input sections by section name suffixes for
1493 // __attribute__((init_priority(N))).
1494 if (name == ".init_array" || name == ".fini_array") {
1495 if (!script->hasSectionsCommand)
1496 sec->sortInitFini();
1497 return;
1498 }
1499
1500 // Sort input sections by the special rule for .ctors and .dtors.
1501 if (name == ".ctors" || name == ".dtors") {
1502 if (!script->hasSectionsCommand)
1503 sec->sortCtorsDtors();
1504 return;
1505 }
1506
1507 // .toc is allocated just after .got and is accessed using GOT-relative
1508 // relocations. Object files compiled with small code model have an
1509 // addressable range of [.got, .got + 0xFFFC] for GOT-relative relocations.
1510 // To reduce the risk of relocation overflow, .toc contents are sorted so that
1511 // sections having smaller relocation offsets are at beginning of .toc
1512 if (config->emachine == EM_PPC64 && name == ".toc") {
1513 if (script->hasSectionsCommand)
1514 return;
1515 assert(sec->sectionCommands.size() == 1)((void)0);
1516 auto *isd = cast<InputSectionDescription>(sec->sectionCommands[0]);
1517 llvm::stable_sort(isd->sections,
1518 [](const InputSection *a, const InputSection *b) -> bool {
1519 return a->file->ppc64SmallCodeModelTocRelocs &&
1520 !b->file->ppc64SmallCodeModelTocRelocs;
1521 });
1522 return;
1523 }
1524}
1525
1526// If no layout was provided by linker script, we want to apply default
1527// sorting for special input sections. This also handles --symbol-ordering-file.
1528template <class ELFT> void Writer<ELFT>::sortInputSections() {
1529 // Build the order once since it is expensive.
1530 DenseMap<const InputSectionBase *, int> order = buildSectionOrder();
1531 maybeShuffle(order);
1532 for (BaseCommand *base : script->sectionCommands)
1533 if (auto *sec = dyn_cast<OutputSection>(base))
1534 sortSection(sec, order);
1535}
1536
1537template <class ELFT> void Writer<ELFT>::sortSections() {
1538 llvm::TimeTraceScope timeScope("Sort sections");
1539 script->adjustSectionsBeforeSorting();
1540
1541 // Don't sort if using -r. It is not necessary and we want to preserve the
1542 // relative order for SHF_LINK_ORDER sections.
1543 if (config->relocatable)
1544 return;
1545
1546 sortInputSections();
1547
1548 for (BaseCommand *base : script->sectionCommands) {
1549 auto *os = dyn_cast<OutputSection>(base);
1550 if (!os)
1551 continue;
1552 os->sortRank = getSectionRank(os);
1553
1554 // We want to assign rude approximation values to outSecOff fields
1555 // to know the relative order of the input sections. We use it for
1556 // sorting SHF_LINK_ORDER sections. See resolveShfLinkOrder().
1557 uint64_t i = 0;
1558 for (InputSection *sec : getInputSections(os))
1559 sec->outSecOff = i++;
1560 }
1561
1562 if (!script->hasSectionsCommand) {
1563 // We know that all the OutputSections are contiguous in this case.
1564 auto isSection = [](BaseCommand *base) { return isa<OutputSection>(base); };
1565 std::stable_sort(
1566 llvm::find_if(script->sectionCommands, isSection),
1567 llvm::find_if(llvm::reverse(script->sectionCommands), isSection).base(),
1568 compareSections);
1569
1570 // Process INSERT commands. From this point onwards the order of
1571 // script->sectionCommands is fixed.
1572 script->processInsertCommands();
1573 return;
1574 }
1575
1576 script->processInsertCommands();
1577
1578 // Orphan sections are sections present in the input files which are
1579 // not explicitly placed into the output file by the linker script.
1580 //
1581 // The sections in the linker script are already in the correct
1582 // order. We have to figuere out where to insert the orphan
1583 // sections.
1584 //
1585 // The order of the sections in the script is arbitrary and may not agree with
1586 // compareSections. This means that we cannot easily define a strict weak
1587 // ordering. To see why, consider a comparison of a section in the script and
1588 // one not in the script. We have a two simple options:
1589 // * Make them equivalent (a is not less than b, and b is not less than a).
1590 // The problem is then that equivalence has to be transitive and we can
1591 // have sections a, b and c with only b in a script and a less than c
1592 // which breaks this property.
1593 // * Use compareSectionsNonScript. Given that the script order doesn't have
1594 // to match, we can end up with sections a, b, c, d where b and c are in the
1595 // script and c is compareSectionsNonScript less than b. In which case d
1596 // can be equivalent to c, a to b and d < a. As a concrete example:
1597 // .a (rx) # not in script
1598 // .b (rx) # in script
1599 // .c (ro) # in script
1600 // .d (ro) # not in script
1601 //
1602 // The way we define an order then is:
1603 // * Sort only the orphan sections. They are in the end right now.
1604 // * Move each orphan section to its preferred position. We try
1605 // to put each section in the last position where it can share
1606 // a PT_LOAD.
1607 //
1608 // There is some ambiguity as to where exactly a new entry should be
1609 // inserted, because Commands contains not only output section
1610 // commands but also other types of commands such as symbol assignment
1611 // expressions. There's no correct answer here due to the lack of the
1612 // formal specification of the linker script. We use heuristics to
1613 // determine whether a new output command should be added before or
1614 // after another commands. For the details, look at shouldSkip
1615 // function.
1616
1617 auto i = script->sectionCommands.begin();
1618 auto e = script->sectionCommands.end();
1619 auto nonScriptI = std::find_if(i, e, [](BaseCommand *base) {
1620 if (auto *sec = dyn_cast<OutputSection>(base))
1621 return sec->sectionIndex == UINT32_MAX0xffffffffU;
1622 return false;
1623 });
1624
1625 // Sort the orphan sections.
1626 std::stable_sort(nonScriptI, e, compareSections);
1627
1628 // As a horrible special case, skip the first . assignment if it is before any
1629 // section. We do this because it is common to set a load address by starting
1630 // the script with ". = 0xabcd" and the expectation is that every section is
1631 // after that.
1632 auto firstSectionOrDotAssignment =
1633 std::find_if(i, e, [](BaseCommand *cmd) { return !shouldSkip(cmd); });
1634 if (firstSectionOrDotAssignment != e &&
1635 isa<SymbolAssignment>(**firstSectionOrDotAssignment))
1636 ++firstSectionOrDotAssignment;
1637 i = firstSectionOrDotAssignment;
1638
1639 while (nonScriptI != e) {
1640 auto pos = findOrphanPos(i, nonScriptI);
1641 OutputSection *orphan = cast<OutputSection>(*nonScriptI);
1642
1643 // As an optimization, find all sections with the same sort rank
1644 // and insert them with one rotate.
1645 unsigned rank = orphan->sortRank;
1646 auto end = std::find_if(nonScriptI + 1, e, [=](BaseCommand *cmd) {
1647 return cast<OutputSection>(cmd)->sortRank != rank;
1648 });
1649 std::rotate(pos, nonScriptI, end);
1650 nonScriptI = end;
1651 }
1652
1653 script->adjustSectionsAfterSorting();
1654}
1655
1656static bool compareByFilePosition(InputSection *a, InputSection *b) {
1657 InputSection *la = a->flags & SHF_LINK_ORDER ? a->getLinkOrderDep() : nullptr;
1658 InputSection *lb = b->flags & SHF_LINK_ORDER ? b->getLinkOrderDep() : nullptr;
1659 // SHF_LINK_ORDER sections with non-zero sh_link are ordered before
1660 // non-SHF_LINK_ORDER sections and SHF_LINK_ORDER sections with zero sh_link.
1661 if (!la || !lb)
1662 return la && !lb;
1663 OutputSection *aOut = la->getParent();
1664 OutputSection *bOut = lb->getParent();
1665
1666 if (aOut != bOut)
1667 return aOut->addr < bOut->addr;
1668 return la->outSecOff < lb->outSecOff;
1669}
1670
1671template <class ELFT> void Writer<ELFT>::resolveShfLinkOrder() {
1672 llvm::TimeTraceScope timeScope("Resolve SHF_LINK_ORDER");
1673 for (OutputSection *sec : outputSections) {
1674 if (!(sec->flags & SHF_LINK_ORDER))
1675 continue;
1676
1677 // The ARM.exidx section use SHF_LINK_ORDER, but we have consolidated
1678 // this processing inside the ARMExidxsyntheticsection::finalizeContents().
1679 if (!config->relocatable && config->emachine == EM_ARM &&
1680 sec->type == SHT_ARM_EXIDX)
1681 continue;
1682
1683 // Link order may be distributed across several InputSectionDescriptions.
1684 // Sorting is performed separately.
1685 std::vector<InputSection **> scriptSections;
1686 std::vector<InputSection *> sections;
1687 for (BaseCommand *base : sec->sectionCommands) {
1688 auto *isd = dyn_cast<InputSectionDescription>(base);
1689 if (!isd)
1690 continue;
1691 bool hasLinkOrder = false;
1692 scriptSections.clear();
1693 sections.clear();
1694 for (InputSection *&isec : isd->sections) {
1695 if (isec->flags & SHF_LINK_ORDER) {
1696 InputSection *link = isec->getLinkOrderDep();
1697 if (link && !link->getParent())
1698 error(toString(isec) + ": sh_link points to discarded section " +
1699 toString(link));
1700 hasLinkOrder = true;
1701 }
1702 scriptSections.push_back(&isec);
1703 sections.push_back(isec);
1704 }
1705 if (hasLinkOrder && errorCount() == 0) {
1706 llvm::stable_sort(sections, compareByFilePosition);
1707 for (int i = 0, n = sections.size(); i != n; ++i)
1708 *scriptSections[i] = sections[i];
1709 }
1710 }
1711 }
1712}
1713
1714static void finalizeSynthetic(SyntheticSection *sec) {
1715 if (sec && sec->isNeeded() && sec->getParent()) {
1716 llvm::TimeTraceScope timeScope("Finalize synthetic sections", sec->name);
1717 sec->finalizeContents();
1718 }
1719}
1720
1721// We need to generate and finalize the content that depends on the address of
1722// InputSections. As the generation of the content may also alter InputSection
1723// addresses we must converge to a fixed point. We do that here. See the comment
1724// in Writer<ELFT>::finalizeSections().
1725template <class ELFT> void Writer<ELFT>::finalizeAddressDependentContent() {
1726 llvm::TimeTraceScope timeScope("Finalize address dependent content");
1727 ThunkCreator tc;
1728 AArch64Err843419Patcher a64p;
1729 ARMErr657417Patcher a32p;
1730 script->assignAddresses();
1731 // .ARM.exidx and SHF_LINK_ORDER do not require precise addresses, but they
1732 // do require the relative addresses of OutputSections because linker scripts
1733 // can assign Virtual Addresses to OutputSections that are not monotonically
1734 // increasing.
1735 for (Partition &part : partitions)
1736 finalizeSynthetic(part.armExidx);
1737 resolveShfLinkOrder();
1738
1739 // Converts call x@GDPLT to call __tls_get_addr
1740 if (config->emachine == EM_HEXAGON)
1741 hexagonTLSSymbolUpdate(outputSections);
1742
1743 int assignPasses = 0;
1744 for (;;) {
1745 bool changed = target->needsThunks && tc.createThunks(outputSections);
1746
1747 // With Thunk Size much smaller than branch range we expect to
1748 // converge quickly; if we get to 15 something has gone wrong.
1749 if (changed && tc.pass >= 15) {
1750 error("thunk creation not converged");
1751 break;
1752 }
1753
1754 if (config->fixCortexA53Errata843419) {
1755 if (changed)
1756 script->assignAddresses();
1757 changed |= a64p.createFixes();
1758 }
1759 if (config->fixCortexA8) {
1760 if (changed)
1761 script->assignAddresses();
1762 changed |= a32p.createFixes();
1763 }
1764
1765 if (in.mipsGot)
1766 in.mipsGot->updateAllocSize();
1767
1768 for (Partition &part : partitions) {
1769 changed |= part.relaDyn->updateAllocSize();
1770 if (part.relrDyn)
1771 changed |= part.relrDyn->updateAllocSize();
1772 }
1773
1774 const Defined *changedSym = script->assignAddresses();
1775 if (!changed) {
1776 // Some symbols may be dependent on section addresses. When we break the
1777 // loop, the symbol values are finalized because a previous
1778 // assignAddresses() finalized section addresses.
1779 if (!changedSym)
1780 break;
1781 if (++assignPasses == 5) {
1782 errorOrWarn("assignment to symbol " + toString(*changedSym) +
1783 " does not converge");
1784 break;
1785 }
1786 }
1787 }
1788
1789 // If addrExpr is set, the address may not be a multiple of the alignment.
1790 // Warn because this is error-prone.
1791 for (BaseCommand *cmd : script->sectionCommands)
1792 if (auto *os = dyn_cast<OutputSection>(cmd))
1793 if (os->addr % os->alignment != 0)
1794 warn("address (0x" + Twine::utohexstr(os->addr) + ") of section " +
1795 os->name + " is not a multiple of alignment (" +
1796 Twine(os->alignment) + ")");
1797}
1798
1799// If Input Sections have been shrunk (basic block sections) then
1800// update symbol values and sizes associated with these sections. With basic
1801// block sections, input sections can shrink when the jump instructions at
1802// the end of the section are relaxed.
1803static void fixSymbolsAfterShrinking() {
1804 for (InputFile *File : objectFiles) {
1805 parallelForEach(File->getSymbols(), [&](Symbol *Sym) {
1806 auto *def = dyn_cast<Defined>(Sym);
1807 if (!def)
1808 return;
1809
1810 const SectionBase *sec = def->section;
1811 if (!sec)
1812 return;
1813
1814 const InputSectionBase *inputSec = dyn_cast<InputSectionBase>(sec->repl);
1815 if (!inputSec || !inputSec->bytesDropped)
1816 return;
1817
1818 const size_t OldSize = inputSec->data().size();
1819 const size_t NewSize = OldSize - inputSec->bytesDropped;
1820
1821 if (def->value > NewSize && def->value <= OldSize) {
1822 LLVM_DEBUG(llvm::dbgs()do { } while (false)
1823 << "Moving symbol " << Sym->getName() << " from "do { } while (false)
1824 << def->value << " to "do { } while (false)
1825 << def->value - inputSec->bytesDropped << " bytes\n")do { } while (false);
1826 def->value -= inputSec->bytesDropped;
1827 return;
1828 }
1829
1830 if (def->value + def->size > NewSize && def->value <= OldSize &&
1831 def->value + def->size <= OldSize) {
1832 LLVM_DEBUG(llvm::dbgs()do { } while (false)
1833 << "Shrinking symbol " << Sym->getName() << " from "do { } while (false)
1834 << def->size << " to " << def->size - inputSec->bytesDroppeddo { } while (false)
1835 << " bytes\n")do { } while (false);
1836 def->size -= inputSec->bytesDropped;
1837 }
1838 });
1839 }
1840}
1841
1842// If basic block sections exist, there are opportunities to delete fall thru
1843// jumps and shrink jump instructions after basic block reordering. This
1844// relaxation pass does that. It is only enabled when --optimize-bb-jumps
1845// option is used.
1846template <class ELFT> void Writer<ELFT>::optimizeBasicBlockJumps() {
1847 assert(config->optimizeBBJumps)((void)0);
1848
1849 script->assignAddresses();
1850 // For every output section that has executable input sections, this
1851 // does the following:
1852 // 1. Deletes all direct jump instructions in input sections that
1853 // jump to the following section as it is not required.
1854 // 2. If there are two consecutive jump instructions, it checks
1855 // if they can be flipped and one can be deleted.
1856 for (OutputSection *os : outputSections) {
1857 if (!(os->flags & SHF_EXECINSTR))
1858 continue;
1859 std::vector<InputSection *> sections = getInputSections(os);
1860 std::vector<unsigned> result(sections.size());
1861 // Delete all fall through jump instructions. Also, check if two
1862 // consecutive jump instructions can be flipped so that a fall
1863 // through jmp instruction can be deleted.
1864 parallelForEachN(0, sections.size(), [&](size_t i) {
1865 InputSection *next = i + 1 < sections.size() ? sections[i + 1] : nullptr;
1866 InputSection &is = *sections[i];
1867 result[i] =
1868 target->deleteFallThruJmpInsn(is, is.getFile<ELFT>(), next) ? 1 : 0;
1869 });
1870 size_t numDeleted = std::count(result.begin(), result.end(), 1);
1871 if (numDeleted > 0) {
1872 script->assignAddresses();
1873 LLVM_DEBUG(llvm::dbgs()do { } while (false)
1874 << "Removing " << numDeleted << " fall through jumps\n")do { } while (false);
1875 }
1876 }
1877
1878 fixSymbolsAfterShrinking();
1879
1880 for (OutputSection *os : outputSections) {
1881 std::vector<InputSection *> sections = getInputSections(os);
1882 for (InputSection *is : sections)
1883 is->trim();
1884 }
1885}
1886
1887// In order to allow users to manipulate linker-synthesized sections,
1888// we had to add synthetic sections to the input section list early,
1889// even before we make decisions whether they are needed. This allows
1890// users to write scripts like this: ".mygot : { .got }".
1891//
1892// Doing it has an unintended side effects. If it turns out that we
1893// don't need a .got (for example) at all because there's no
1894// relocation that needs a .got, we don't want to emit .got.
1895//
1896// To deal with the above problem, this function is called after
1897// scanRelocations is called to remove synthetic sections that turn
1898// out to be empty.
1899static void removeUnusedSyntheticSections() {
1900 // All input synthetic sections that can be empty are placed after
1901 // all regular ones. Reverse iterate to find the first synthetic section
1902 // after a non-synthetic one which will be our starting point.
1903 auto start = std::find_if(inputSections.rbegin(), inputSections.rend(),
1904 [](InputSectionBase *s) {
1905 return !isa<SyntheticSection>(s);
1906 })
1907 .base();
1908
1909 DenseSet<InputSectionDescription *> isdSet;
1910 // Mark unused synthetic sections for deletion
1911 auto end = std::stable_partition(
20
Calling 'stable_partition<std::__wrap_iter<lld::elf::InputSectionBase **>, (lambda at /usr/src/gnu/usr.bin/clang/liblldELF/../../../llvm/lld/ELF/Writer.cpp:1912:35)>'
1912 start, inputSections.end(), [&](InputSectionBase *s) {
1913 SyntheticSection *ss = dyn_cast<SyntheticSection>(s);
25
Assuming 's' is not a 'SyntheticSection'
26
'ss' initialized to a null pointer value
1914 OutputSection *os = ss->getParent();
27
Called C++ object pointer is null
1915 if (!os || ss->isNeeded())
1916 return true;
1917
1918 // If we reach here, then ss is an unused synthetic section and we want
1919 // to remove it from the corresponding input section description, and
1920 // orphanSections.
1921 for (BaseCommand *b : os->sectionCommands)
1922 if (auto *isd = dyn_cast<InputSectionDescription>(b))
1923 isdSet.insert(isd);
1924
1925 llvm::erase_if(
1926 script->orphanSections,
1927 [=](const InputSectionBase *isec) { return isec == ss; });
1928
1929 return false;
1930 });
1931
1932 DenseSet<InputSectionBase *> unused(end, inputSections.end());
1933 for (auto *isd : isdSet)
1934 llvm::erase_if(isd->sections,
1935 [=](InputSection *isec) { return unused.count(isec); });
1936
1937 // Erase unused synthetic sections.
1938 inputSections.erase(end, inputSections.end());
1939}
1940
1941// Create output section objects and add them to OutputSections.
1942template <class ELFT> void Writer<ELFT>::finalizeSections() {
1943 Out::preinitArray = findSection(".preinit_array");
1944 Out::initArray = findSection(".init_array");
1945 Out::finiArray = findSection(".fini_array");
1946
1947 // The linker needs to define SECNAME_start, SECNAME_end and SECNAME_stop
1948 // symbols for sections, so that the runtime can get the start and end
1949 // addresses of each section by section name. Add such symbols.
1950 if (!config->relocatable) {
1
Assuming field 'relocatable' is true
2
Taking false branch
1951 addStartEndSymbols();
1952 for (BaseCommand *base : script->sectionCommands)
1953 if (auto *sec = dyn_cast<OutputSection>(base))
1954 addStartStopSymbols(sec);
1955 }
1956
1957 // Add _DYNAMIC symbol. Unlike GNU gold, our _DYNAMIC symbol has no type.
1958 // It should be okay as no one seems to care about the type.
1959 // Even the author of gold doesn't remember why gold behaves that way.
1960 // https://sourceware.org/ml/binutils/2002-03/msg00360.html
1961 if (mainPart->dynamic->parent)
3
Assuming field 'parent' is null
4
Taking false branch
1962 symtab->addSymbol(Defined{/*file=*/nullptr, "_DYNAMIC", STB_WEAK,
1963 STV_HIDDEN, STT_NOTYPE,
1964 /*value=*/0, /*size=*/0, mainPart->dynamic});
1965
1966 // Define __rel[a]_iplt_{start,end} symbols if needed.
1967 addRelIpltSymbols();
1968
1969 // RISC-V's gp can address +/- 2 KiB, set it to .sdata + 0x800. This symbol
1970 // should only be defined in an executable. If .sdata does not exist, its
1971 // value/section does not matter but it has to be relative, so set its
1972 // st_shndx arbitrarily to 1 (Out::elfHeader).
1973 if (config->emachine == EM_RISCV && !config->shared) {
5
Assuming field 'emachine' is not equal to EM_RISCV
1974 OutputSection *sec = findSection(".sdata");
1975 ElfSym::riscvGlobalPointer =
1976 addOptionalRegular("__global_pointer$", sec ? sec : Out::elfHeader,
1977 0x800, STV_DEFAULT, STB_GLOBAL);
1978 }
1979
1980 if (config->emachine == EM_X86_64) {
6
Assuming field 'emachine' is not equal to EM_X86_64
7
Taking false branch
1981 // On targets that support TLSDESC, _TLS_MODULE_BASE_ is defined in such a
1982 // way that:
1983 //
1984 // 1) Without relaxation: it produces a dynamic TLSDESC relocation that
1985 // computes 0.
1986 // 2) With LD->LE relaxation: _TLS_MODULE_BASE_@tpoff = 0 (lowest address in
1987 // the TLS block).
1988 //
1989 // 2) is special cased in @tpoff computation. To satisfy 1), we define it as
1990 // an absolute symbol of zero. This is different from GNU linkers which
1991 // define _TLS_MODULE_BASE_ relative to the first TLS section.
1992 Symbol *s = symtab->find("_TLS_MODULE_BASE_");
1993 if (s && s->isUndefined()) {
1994 s->resolve(Defined{/*file=*/nullptr, s->getName(), STB_GLOBAL, STV_HIDDEN,
1995 STT_TLS, /*value=*/0, 0,
1996 /*section=*/nullptr});
1997 ElfSym::tlsModuleBase = cast<Defined>(s);
1998 }
1999 }
2000
2001 {
2002 llvm::TimeTraceScope timeScope("Finalize .eh_frame");
2003 // This responsible for splitting up .eh_frame section into
2004 // pieces. The relocation scan uses those pieces, so this has to be
2005 // earlier.
2006 for (Partition &part : partitions)
2007 finalizeSynthetic(part.ehFrame);
2008 }
2009
2010 for (Symbol *sym : symtab->symbols())
2011 sym->isPreemptible = computeIsPreemptible(*sym);
2012
2013 // Change values of linker-script-defined symbols from placeholders (assigned
2014 // by declareSymbols) to actual definitions.
2015 script->processSymbolAssignments();
2016
2017 {
2018 llvm::TimeTraceScope timeScope("Scan relocations");
2019 // Scan relocations. This must be done after every symbol is declared so
2020 // that we can correctly decide if a dynamic relocation is needed. This is
2021 // called after processSymbolAssignments() because it needs to know whether
2022 // a linker-script-defined symbol is absolute.
2023 ppc64noTocRelax.clear();
2024 if (!config->relocatable) {
8
Assuming field 'relocatable' is true
9
Taking false branch
2025 forEachRelSec(scanRelocations<ELFT>);
2026 reportUndefinedSymbols<ELFT>();
2027 }
2028 }
2029
2030 if (in.plt && in.plt->isNeeded())
10
Assuming field 'plt' is null
2031 in.plt->addSymbols();
2032 if (in.iplt && in.iplt->isNeeded())
11
Assuming field 'iplt' is null
2033 in.iplt->addSymbols();
2034
2035 if (config->unresolvedSymbolsInShlib != UnresolvedPolicy::Ignore) {
12
Assuming field 'unresolvedSymbolsInShlib' is equal to Ignore
13
Taking false branch
2036 auto diagnose =
2037 config->unresolvedSymbolsInShlib == UnresolvedPolicy::ReportError
2038 ? errorOrWarn
2039 : warn;
2040 // Error on undefined symbols in a shared object, if all of its DT_NEEDED
2041 // entries are seen. These cases would otherwise lead to runtime errors
2042 // reported by the dynamic linker.
2043 //
2044 // ld.bfd traces all DT_NEEDED to emulate the logic of the dynamic linker to
2045 // catch more cases. That is too much for us. Our approach resembles the one
2046 // used in ld.gold, achieves a good balance to be useful but not too smart.
2047 for (SharedFile *file : sharedFiles) {
2048 bool allNeededIsKnown =
2049 llvm::all_of(file->dtNeeded, [&](StringRef needed) {
2050 return symtab->soNames.count(needed);
2051 });
2052 if (!allNeededIsKnown)
2053 continue;
2054 for (Symbol *sym : file->requiredSymbols)
2055 if (sym->isUndefined() && !sym->isWeak())
2056 diagnose(toString(file) + ": undefined reference to " +
2057 toString(*sym) + " [--no-allow-shlib-undefined]");
2058 }
2059 }
2060
2061 {
2062 llvm::TimeTraceScope timeScope("Add symbols to symtabs");
2063 // Now that we have defined all possible global symbols including linker-
2064 // synthesized ones. Visit all symbols to give the finishing touches.
2065 for (Symbol *sym : symtab->symbols()) {
2066 if (!includeInSymtab(*sym))
2067 continue;
2068 if (in.symTab)
2069 in.symTab->addSymbol(sym);
2070
2071 if (sym->includeInDynsym()) {
2072 partitions[sym->partition - 1].dynSymTab->addSymbol(sym);
2073 if (auto *file = dyn_cast_or_null<SharedFile>(sym->file))
2074 if (file->isNeeded && !sym->isUndefined())
2075 addVerneed(sym);
2076 }
2077 }
2078
2079 // We also need to scan the dynamic relocation tables of the other
2080 // partitions and add any referenced symbols to the partition's dynsym.
2081 for (Partition &part : MutableArrayRef<Partition>(partitions).slice(1)) {
14
Assuming '__begin2' is equal to '__end2'
2082 DenseSet<Symbol *> syms;
2083 for (const SymbolTableEntry &e : part.dynSymTab->getSymbols())
2084 syms.insert(e.sym);
2085 for (DynamicReloc &reloc : part.relaDyn->relocs)
2086 if (reloc.sym && reloc.needsDynSymIndex() &&
2087 syms.insert(reloc.sym).second)
2088 part.dynSymTab->addSymbol(reloc.sym);
2089 }
2090 }
2091
2092 // Do not proceed if there was an undefined symbol.
2093 if (errorCount())
15
Assuming the condition is false
16
Taking false branch
2094 return;
2095
2096 if (in.mipsGot)
17
Assuming field 'mipsGot' is null
18
Taking false branch
2097 in.mipsGot->build();
2098
2099 removeUnusedSyntheticSections();
19
Calling 'removeUnusedSyntheticSections'
2100 script->diagnoseOrphanHandling();
2101
2102 sortSections();
2103
2104 // Now that we have the final list, create a list of all the
2105 // OutputSections for convenience.
2106 for (BaseCommand *base : script->sectionCommands)
2107 if (auto *sec = dyn_cast<OutputSection>(base))
2108 outputSections.push_back(sec);
2109
2110 // Prefer command line supplied address over other constraints.
2111 for (OutputSection *sec : outputSections) {
2112 auto i = config->sectionStartMap.find(sec->name);
2113 if (i != config->sectionStartMap.end())
2114 sec->addrExpr = [=] { return i->second; };
2115 }
2116
2117 // With the outputSections available check for GDPLT relocations
2118 // and add __tls_get_addr symbol if needed.
2119 if (config->emachine == EM_HEXAGON && hexagonNeedsTLSSymbol(outputSections)) {
2120 Symbol *sym = symtab->addSymbol(Undefined{
2121 nullptr, "__tls_get_addr", STB_GLOBAL, STV_DEFAULT, STT_NOTYPE});
2122 sym->isPreemptible = true;
2123 partitions[0].dynSymTab->addSymbol(sym);
2124 }
2125
2126 // This is a bit of a hack. A value of 0 means undef, so we set it
2127 // to 1 to make __ehdr_start defined. The section number is not
2128 // particularly relevant.
2129 Out::elfHeader->sectionIndex = 1;
2130
2131 for (size_t i = 0, e = outputSections.size(); i != e; ++i) {
2132 OutputSection *sec = outputSections[i];
2133 sec->sectionIndex = i + 1;
2134 sec->shName = in.shStrTab->addString(sec->name);
2135 }
2136
2137 // Binary and relocatable output does not have PHDRS.
2138 // The headers have to be created before finalize as that can influence the
2139 // image base and the dynamic section on mips includes the image base.
2140 if (!config->relocatable && !config->oFormatBinary) {
2141 for (Partition &part : partitions) {
2142 part.phdrs = script->hasPhdrsCommands() ? script->createPhdrs()
2143 : createPhdrs(part);
2144 if (config->emachine == EM_ARM) {
2145 // PT_ARM_EXIDX is the ARM EHABI equivalent of PT_GNU_EH_FRAME
2146 addPhdrForSection(part, SHT_ARM_EXIDX, PT_ARM_EXIDX, PF_R);
2147 }
2148 if (config->emachine == EM_MIPS) {
2149 // Add separate segments for MIPS-specific sections.
2150 addPhdrForSection(part, SHT_MIPS_REGINFO, PT_MIPS_REGINFO, PF_R);
2151 addPhdrForSection(part, SHT_MIPS_OPTIONS, PT_MIPS_OPTIONS, PF_R);
2152 addPhdrForSection(part, SHT_MIPS_ABIFLAGS, PT_MIPS_ABIFLAGS, PF_R);
2153 }
2154 }
2155 Out::programHeaders->size = sizeof(Elf_Phdr) * mainPart->phdrs.size();
2156
2157 // Find the TLS segment. This happens before the section layout loop so that
2158 // Android relocation packing can look up TLS symbol addresses. We only need
2159 // to care about the main partition here because all TLS symbols were moved
2160 // to the main partition (see MarkLive.cpp).
2161 for (PhdrEntry *p : mainPart->phdrs)
2162 if (p->p_type == PT_TLS)
2163 Out::tlsPhdr = p;
2164 }
2165
2166 // Some symbols are defined in term of program headers. Now that we
2167 // have the headers, we can find out which sections they point to.
2168 setReservedSymbolSections();
2169
2170 {
2171 llvm::TimeTraceScope timeScope("Finalize synthetic sections");
2172
2173 finalizeSynthetic(in.bss);
2174 finalizeSynthetic(in.bssRelRo);
2175 finalizeSynthetic(in.symTabShndx);
2176 finalizeSynthetic(in.shStrTab);
2177 finalizeSynthetic(in.strTab);
2178 finalizeSynthetic(in.got);
2179 finalizeSynthetic(in.mipsGot);
2180 finalizeSynthetic(in.igotPlt);
2181 finalizeSynthetic(in.gotPlt);
2182 finalizeSynthetic(in.relaIplt);
2183 finalizeSynthetic(in.relaPlt);
2184 finalizeSynthetic(in.plt);
2185 finalizeSynthetic(in.iplt);
2186 finalizeSynthetic(in.ppc32Got2);
2187 finalizeSynthetic(in.partIndex);
2188
2189 // Dynamic section must be the last one in this list and dynamic
2190 // symbol table section (dynSymTab) must be the first one.
2191 for (Partition &part : partitions) {
2192 finalizeSynthetic(part.dynSymTab);
2193 finalizeSynthetic(part.gnuHashTab);
2194 finalizeSynthetic(part.hashTab);
2195 finalizeSynthetic(part.verDef);
2196 finalizeSynthetic(part.relaDyn);
2197 finalizeSynthetic(part.relrDyn);
2198 finalizeSynthetic(part.ehFrameHdr);
2199 finalizeSynthetic(part.verSym);
2200 finalizeSynthetic(part.verNeed);
2201 finalizeSynthetic(part.dynamic);
2202 }
2203 }
2204
2205 if (!script->hasSectionsCommand && !config->relocatable)
2206 fixSectionAlignments();
2207
2208 // This is used to:
2209 // 1) Create "thunks":
2210 // Jump instructions in many ISAs have small displacements, and therefore
2211 // they cannot jump to arbitrary addresses in memory. For example, RISC-V
2212 // JAL instruction can target only +-1 MiB from PC. It is a linker's
2213 // responsibility to create and insert small pieces of code between
2214 // sections to extend the ranges if jump targets are out of range. Such
2215 // code pieces are called "thunks".
2216 //
2217 // We add thunks at this stage. We couldn't do this before this point
2218 // because this is the earliest point where we know sizes of sections and
2219 // their layouts (that are needed to determine if jump targets are in
2220 // range).
2221 //
2222 // 2) Update the sections. We need to generate content that depends on the
2223 // address of InputSections. For example, MIPS GOT section content or
2224 // android packed relocations sections content.
2225 //
2226 // 3) Assign the final values for the linker script symbols. Linker scripts
2227 // sometimes using forward symbol declarations. We want to set the correct
2228 // values. They also might change after adding the thunks.
2229 finalizeAddressDependentContent();
2230 if (errorCount())
2231 return;
2232
2233 {
2234 llvm::TimeTraceScope timeScope("Finalize synthetic sections");
2235 // finalizeAddressDependentContent may have added local symbols to the
2236 // static symbol table.
2237 finalizeSynthetic(in.symTab);
2238 finalizeSynthetic(in.ppc64LongBranchTarget);
2239 }
2240
2241 // Relaxation to delete inter-basic block jumps created by basic block
2242 // sections. Run after in.symTab is finalized as optimizeBasicBlockJumps
2243 // can relax jump instructions based on symbol offset.
2244 if (config->optimizeBBJumps)
2245 optimizeBasicBlockJumps();
2246
2247 // Fill other section headers. The dynamic table is finalized
2248 // at the end because some tags like RELSZ depend on result
2249 // of finalizing other sections.
2250 for (OutputSection *sec : outputSections)
2251 sec->finalize();
2252}
2253
2254// Ensure data sections are not mixed with executable sections when
2255// -execute-only is used. -execute-only is a feature to make pages executable
2256// but not readable, and the feature is currently supported only on AArch64.
2257template <class ELFT> void Writer<ELFT>::checkExecuteOnly() {
2258 if (!config->executeOnly)
2259 return;
2260
2261 for (OutputSection *os : outputSections)
2262 if (os->flags & SHF_EXECINSTR)
2263 for (InputSection *isec : getInputSections(os))
2264 if (!(isec->flags & SHF_EXECINSTR))
2265 error("cannot place " + toString(isec) + " into " + toString(os->name) +
2266 ": -execute-only does not support intermingling data and code");
2267}
2268
2269// The linker is expected to define SECNAME_start and SECNAME_end
2270// symbols for a few sections. This function defines them.
2271template <class ELFT> void Writer<ELFT>::addStartEndSymbols() {
2272 // If a section does not exist, there's ambiguity as to how we
2273 // define _start and _end symbols for an init/fini section. Since
2274 // the loader assume that the symbols are always defined, we need to
2275 // always define them. But what value? The loader iterates over all
2276 // pointers between _start and _end to run global ctors/dtors, so if
2277 // the section is empty, their symbol values don't actually matter
2278 // as long as _start and _end point to the same location.
2279 //
2280 // That said, we don't want to set the symbols to 0 (which is
2281 // probably the simplest value) because that could cause some
2282 // program to fail to link due to relocation overflow, if their
2283 // program text is above 2 GiB. We use the address of the .text
2284 // section instead to prevent that failure.
2285 //
2286 // In rare situations, the .text section may not exist. If that's the
2287 // case, use the image base address as a last resort.
2288 OutputSection *Default = findSection(".text");
2289 if (!Default)
2290 Default = Out::elfHeader;
2291
2292 auto define = [=](StringRef start, StringRef end, OutputSection *os) {
2293 if (os) {
2294 addOptionalRegular(start, os, 0);
2295 addOptionalRegular(end, os, -1);
2296 } else {
2297 addOptionalRegular(start, Default, 0);
2298 addOptionalRegular(end, Default, 0);
2299 }
2300 };
2301
2302 define("__preinit_array_start", "__preinit_array_end", Out::preinitArray);
2303 define("__init_array_start", "__init_array_end", Out::initArray);
2304 define("__fini_array_start", "__fini_array_end", Out::finiArray);
2305
2306 if (OutputSection *sec = findSection(".ARM.exidx"))
2307 define("__exidx_start", "__exidx_end", sec);
2308}
2309
2310// If a section name is valid as a C identifier (which is rare because of
2311// the leading '.'), linkers are expected to define __start_<secname> and
2312// __stop_<secname> symbols. They are at beginning and end of the section,
2313// respectively. This is not requested by the ELF standard, but GNU ld and
2314// gold provide the feature, and used by many programs.
2315template <class ELFT>
2316void Writer<ELFT>::addStartStopSymbols(OutputSection *sec) {
2317 StringRef s = sec->name;
2318 if (!isValidCIdentifier(s))
2319 return;
2320 addOptionalRegular(saver.save("__start_" + s), sec, 0,
2321 config->zStartStopVisibility);
2322 addOptionalRegular(saver.save("__stop_" + s), sec, -1,
2323 config->zStartStopVisibility);
2324}
2325
2326static bool needsPtLoad(OutputSection *sec) {
2327 if (!(sec->flags & SHF_ALLOC))
2328 return false;
2329
2330 // Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
2331 // responsible for allocating space for them, not the PT_LOAD that
2332 // contains the TLS initialization image.
2333 if ((sec->flags & SHF_TLS) && sec->type == SHT_NOBITS)
2334 return false;
2335 return true;
2336}
2337
2338// Linker scripts are responsible for aligning addresses. Unfortunately, most
2339// linker scripts are designed for creating two PT_LOADs only, one RX and one
2340// RW. This means that there is no alignment in the RO to RX transition and we
2341// cannot create a PT_LOAD there.
2342static uint64_t computeFlags(uint64_t flags) {
2343 if (config->omagic)
2344 return PF_R | PF_W | PF_X;
2345 if (config->executeOnly && (flags & PF_X))
2346 return flags & ~PF_R;
2347 if (config->singleRoRx && !(flags & PF_W))
2348 return flags | PF_X;
2349 return flags;
2350}
2351
2352// Decide which program headers to create and which sections to include in each
2353// one.
2354template <class ELFT>
2355std::vector<PhdrEntry *> Writer<ELFT>::createPhdrs(Partition &part) {
2356 std::vector<PhdrEntry *> ret;
2357 auto addHdr = [&](unsigned type, unsigned flags) -> PhdrEntry * {
2358 ret.push_back(make<PhdrEntry>(type, flags));
2359 return ret.back();
2360 };
2361
2362 unsigned partNo = part.getNumber();
2363 bool isMain = partNo == 1;
2364
2365 // Add the first PT_LOAD segment for regular output sections.
2366 uint64_t flags = computeFlags(PF_R);
2367 PhdrEntry *load = nullptr;
2368
2369 // nmagic or omagic output does not have PT_PHDR, PT_INTERP, or the readonly
2370 // PT_LOAD.
2371 if (!config->nmagic && !config->omagic) {
2372 // The first phdr entry is PT_PHDR which describes the program header
2373 // itself.
2374 if (isMain)
2375 addHdr(PT_PHDR, PF_R)->add(Out::programHeaders);
2376 else
2377 addHdr(PT_PHDR, PF_R)->add(part.programHeaders->getParent());
2378
2379 // PT_INTERP must be the second entry if exists.
2380 if (OutputSection *cmd = findSection(".interp", partNo))
2381 addHdr(PT_INTERP, cmd->getPhdrFlags())->add(cmd);
2382
2383 // Add the headers. We will remove them if they don't fit.
2384 // In the other partitions the headers are ordinary sections, so they don't
2385 // need to be added here.
2386 if (isMain) {
2387 load = addHdr(PT_LOAD, flags);
2388 load->add(Out::elfHeader);
2389 load->add(Out::programHeaders);
2390 }
2391 }
2392
2393 // PT_GNU_RELRO includes all sections that should be marked as
2394 // read-only by dynamic linker after processing relocations.
2395 // Current dynamic loaders only support one PT_GNU_RELRO PHDR, give
2396 // an error message if more than one PT_GNU_RELRO PHDR is required.
2397 PhdrEntry *relRo = make<PhdrEntry>(PT_GNU_RELRO, PF_R);
2398 bool inRelroPhdr = false;
2399 OutputSection *relroEnd = nullptr;
2400 for (OutputSection *sec : outputSections) {
2401 if (sec->partition != partNo || !needsPtLoad(sec))
2402 continue;
2403 if (isRelroSection(sec)) {
2404 inRelroPhdr = true;
2405 if (!relroEnd)
2406 relRo->add(sec);
2407 else
2408 error("section: " + sec->name + " is not contiguous with other relro" +
2409 " sections");
2410 } else if (inRelroPhdr) {
2411 inRelroPhdr = false;
2412 relroEnd = sec;
2413 }
2414 }
2415
2416 for (OutputSection *sec : outputSections) {
2417 if (!needsPtLoad(sec))
2418 continue;
2419
2420 // Normally, sections in partitions other than the current partition are
2421 // ignored. But partition number 255 is a special case: it contains the
2422 // partition end marker (.part.end). It needs to be added to the main
2423 // partition so that a segment is created for it in the main partition,
2424 // which will cause the dynamic loader to reserve space for the other
2425 // partitions.
2426 if (sec->partition != partNo) {
2427 if (isMain && sec->partition == 255)
2428 addHdr(PT_LOAD, computeFlags(sec->getPhdrFlags()))->add(sec);
2429 continue;
2430 }
2431
2432 // Segments are contiguous memory regions that has the same attributes
2433 // (e.g. executable or writable). There is one phdr for each segment.
2434 // Therefore, we need to create a new phdr when the next section has
2435 // different flags or is loaded at a discontiguous address or memory
2436 // region using AT or AT> linker script command, respectively. At the same
2437 // time, we don't want to create a separate load segment for the headers,
2438 // even if the first output section has an AT or AT> attribute.
2439 uint64_t newFlags = computeFlags(sec->getPhdrFlags());
2440 bool sameLMARegion =
2441 load && !sec->lmaExpr && sec->lmaRegion == load->firstSec->lmaRegion;
2442 if (!(load && newFlags == flags && sec != relroEnd &&
2443 sec->memRegion == load->firstSec->memRegion &&
2444 (sameLMARegion || load->lastSec == Out::programHeaders))) {
2445 load = addHdr(PT_LOAD, newFlags);
2446 flags = newFlags;
2447 }
2448
2449 load->add(sec);
2450 }
2451
2452 // Add a TLS segment if any.
2453 PhdrEntry *tlsHdr = make<PhdrEntry>(PT_TLS, PF_R);
2454 for (OutputSection *sec : outputSections)
2455 if (sec->partition == partNo && sec->flags & SHF_TLS)
2456 tlsHdr->add(sec);
2457 if (tlsHdr->firstSec)
2458 ret.push_back(tlsHdr);
2459
2460 // Add an entry for .dynamic.
2461 if (OutputSection *sec = part.dynamic->getParent())
2462 addHdr(PT_DYNAMIC, sec->getPhdrFlags())->add(sec);
2463
2464 if (relRo->firstSec)
2465 ret.push_back(relRo);
2466
2467 // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
2468 if (part.ehFrame->isNeeded() && part.ehFrameHdr &&
2469 part.ehFrame->getParent() && part.ehFrameHdr->getParent())
2470 addHdr(PT_GNU_EH_FRAME, part.ehFrameHdr->getParent()->getPhdrFlags())
2471 ->add(part.ehFrameHdr->getParent());
2472
2473 // PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
2474 // the dynamic linker fill the segment with random data.
2475 if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
2476 addHdr(PT_OPENBSD_RANDOMIZE, cmd->getPhdrFlags())->add(cmd);
2477
2478 if (config->zGnustack != GnuStackKind::None) {
2479 // PT_GNU_STACK is a special section to tell the loader to make the
2480 // pages for the stack non-executable. If you really want an executable
2481 // stack, you can pass -z execstack, but that's not recommended for
2482 // security reasons.
2483 unsigned perm = PF_R | PF_W;
2484 if (config->zGnustack == GnuStackKind::Exec)
2485 perm |= PF_X;
2486 addHdr(PT_GNU_STACK, perm)->p_memsz = config->zStackSize;
2487 }
2488
2489 // PT_OPENBSD_WXNEEDED is a OpenBSD-specific header to mark the executable
2490 // is expected to perform W^X violations, such as calling mprotect(2) or
2491 // mmap(2) with PROT_WRITE | PROT_EXEC, which is prohibited by default on
2492 // OpenBSD.
2493 if (config->zWxneeded)
2494 addHdr(PT_OPENBSD_WXNEEDED, PF_X);
2495
2496 if (OutputSection *cmd = findSection(".note.gnu.property", partNo))
2497 addHdr(PT_GNU_PROPERTY, PF_R)->add(cmd);
2498
2499 // Create one PT_NOTE per a group of contiguous SHT_NOTE sections with the
2500 // same alignment.
2501 PhdrEntry *note = nullptr;
2502 for (OutputSection *sec : outputSections) {
2503 if (sec->partition != partNo)
2504 continue;
2505 if (sec->type == SHT_NOTE && (sec->flags & SHF_ALLOC)) {
2506 if (!note || sec->lmaExpr || note->lastSec->alignment != sec->alignment)
2507 note = addHdr(PT_NOTE, PF_R);
2508 note->add(sec);
2509 } else {
2510 note = nullptr;
2511 }
2512 }
2513 return ret;
2514}
2515
2516template <class ELFT>
2517void Writer<ELFT>::addPhdrForSection(Partition &part, unsigned shType,
2518 unsigned pType, unsigned pFlags) {
2519 unsigned partNo = part.getNumber();
2520 auto i = llvm::find_if(outputSections, [=](OutputSection *cmd) {
2521 return cmd->partition == partNo && cmd->type == shType;
2522 });
2523 if (i == outputSections.end())
2524 return;
2525
2526 PhdrEntry *entry = make<PhdrEntry>(pType, pFlags);
2527 entry->add(*i);
2528 part.phdrs.push_back(entry);
2529}
2530
2531// Place the first section of each PT_LOAD to a different page (of maxPageSize).
2532// This is achieved by assigning an alignment expression to addrExpr of each
2533// such section.
2534template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
2535 const PhdrEntry *prev;
2536 auto pageAlign = [&](const PhdrEntry *p) {
2537 OutputSection *cmd = p->firstSec;
2538 if (!cmd)
2539 return;
2540 cmd->alignExpr = [align = cmd->alignment]() { return align; };
2541 if (!cmd->addrExpr) {
2542 // Prefer advancing to align(dot, maxPageSize) + dot%maxPageSize to avoid
2543 // padding in the file contents.
2544 //
2545 // When -z separate-code is used we must not have any overlap in pages
2546 // between an executable segment and a non-executable segment. We align to
2547 // the next maximum page size boundary on transitions between executable
2548 // and non-executable segments.
2549 //
2550 // SHT_LLVM_PART_EHDR marks the start of a partition. The partition
2551 // sections will be extracted to a separate file. Align to the next
2552 // maximum page size boundary so that we can find the ELF header at the
2553 // start. We cannot benefit from overlapping p_offset ranges with the
2554 // previous segment anyway.
2555 if (config->zSeparate == SeparateSegmentKind::Loadable ||
2556 (config->zSeparate == SeparateSegmentKind::Code && prev &&
2557 (prev->p_flags & PF_X) != (p->p_flags & PF_X)) ||
2558 cmd->type == SHT_LLVM_PART_EHDR)
2559 cmd->addrExpr = [] {
2560 return alignTo(script->getDot(), config->maxPageSize);
2561 };
2562 // PT_TLS is at the start of the first RW PT_LOAD. If `p` includes PT_TLS,
2563 // it must be the RW. Align to p_align(PT_TLS) to make sure
2564 // p_vaddr(PT_LOAD)%p_align(PT_LOAD) = 0. Otherwise, if
2565 // sh_addralign(.tdata) < sh_addralign(.tbss), we will set p_align(PT_TLS)
2566 // to sh_addralign(.tbss), while p_vaddr(PT_TLS)=p_vaddr(PT_LOAD) may not
2567 // be congruent to 0 modulo p_align(PT_TLS).
2568 //
2569 // Technically this is not required, but as of 2019, some dynamic loaders
2570 // don't handle p_vaddr%p_align != 0 correctly, e.g. glibc (i386 and
2571 // x86-64) doesn't make runtime address congruent to p_vaddr modulo
2572 // p_align for dynamic TLS blocks (PR/24606), FreeBSD rtld has the same
2573 // bug, musl (TLS Variant 1 architectures) before 1.1.23 handled TLS
2574 // blocks correctly. We need to keep the workaround for a while.
2575 else if (Out::tlsPhdr && Out::tlsPhdr->firstSec == p->firstSec)
2576 cmd->addrExpr = [] {
2577 return alignTo(script->getDot(), config->maxPageSize) +
2578 alignTo(script->getDot() % config->maxPageSize,
2579 Out::tlsPhdr->p_align);
2580 };
2581 else
2582 cmd->addrExpr = [] {
2583 return alignTo(script->getDot(), config->maxPageSize) +
2584 script->getDot() % config->maxPageSize;
2585 };
2586 }
2587 };
2588
2589#ifdef __OpenBSD__1
2590 // On i386, produce binaries that are compatible with our W^X implementation
2591 if (config->emachine == EM_386) {
2592 auto NXAlign = [](OutputSection *Cmd) {
2593 if (Cmd && !Cmd->addrExpr)
2594 Cmd->addrExpr = [=] {
2595 return alignTo(script->getDot(), 0x20000000);
2596 };
2597 };
2598
2599 for (Partition &part : partitions) {
2600 PhdrEntry *firstRW = nullptr;
2601 for (PhdrEntry *P : part.phdrs) {
2602 if (P->p_type == PT_LOAD && (P->p_flags & PF_W)) {
2603 firstRW = P;
2604 break;
2605 }
2606 }
2607
2608 if (firstRW)
2609 NXAlign(firstRW->firstSec);
2610 }
2611 }
2612#endif
2613
2614 for (Partition &part : partitions) {
2615 prev = nullptr;
2616 for (const PhdrEntry *p : part.phdrs)
2617 if (p->p_type == PT_LOAD && p->firstSec) {
2618 pageAlign(p);
2619 prev = p;
2620 }
2621 }
2622}
2623
2624// Compute an in-file position for a given section. The file offset must be the
2625// same with its virtual address modulo the page size, so that the loader can
2626// load executables without any address adjustment.
2627static uint64_t computeFileOffset(OutputSection *os, uint64_t off) {
2628 // The first section in a PT_LOAD has to have congruent offset and address
2629 // modulo the maximum page size.
2630 if (os->ptLoad && os->ptLoad->firstSec == os)
2631 return alignTo(off, os->ptLoad->p_align, os->addr);
2632
2633 // File offsets are not significant for .bss sections other than the first one
2634 // in a PT_LOAD. By convention, we keep section offsets monotonically
2635 // increasing rather than setting to zero.
2636 if (os->type == SHT_NOBITS)
2637 return off;
2638
2639 // If the section is not in a PT_LOAD, we just have to align it.
2640 if (!os->ptLoad)
2641 return alignTo(off, os->alignment);
2642
2643 // If two sections share the same PT_LOAD the file offset is calculated
2644 // using this formula: Off2 = Off1 + (VA2 - VA1).
2645 OutputSection *first = os->ptLoad->firstSec;
2646 return first->offset + os->addr - first->addr;
2647}
2648
2649// Set an in-file position to a given section and returns the end position of
2650// the section.
2651static uint64_t setFileOffset(OutputSection *os, uint64_t off) {
2652 off = computeFileOffset(os, off);
2653 os->offset = off;
2654
2655 if (os->type == SHT_NOBITS)
2656 return off;
2657 return off + os->size;
2658}
2659
2660template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
2661 // Compute the minimum LMA of all non-empty non-NOBITS sections as minAddr.
2662 auto needsOffset = [](OutputSection &sec) {
2663 return sec.type != SHT_NOBITS && (sec.flags & SHF_ALLOC) && sec.size > 0;
2664 };
2665 uint64_t minAddr = UINT64_MAX0xffffffffffffffffULL;
2666 for (OutputSection *sec : outputSections)
2667 if (needsOffset(*sec)) {
2668 sec->offset = sec->getLMA();
2669 minAddr = std::min(minAddr, sec->offset);
2670 }
2671
2672 // Sections are laid out at LMA minus minAddr.
2673 fileSize = 0;
2674 for (OutputSection *sec : outputSections)
2675 if (needsOffset(*sec)) {
2676 sec->offset -= minAddr;
2677 fileSize = std::max(fileSize, sec->offset + sec->size);
2678 }
2679}
2680
2681static std::string rangeToString(uint64_t addr, uint64_t len) {
2682 return "[0x" + utohexstr(addr) + ", 0x" + utohexstr(addr + len - 1) + "]";
2683}
2684
2685// Assign file offsets to output sections.
2686template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
2687 uint64_t off = 0;
2688 off = setFileOffset(Out::elfHeader, off);
2689 off = setFileOffset(Out::programHeaders, off);
2690
2691 PhdrEntry *lastRX = nullptr;
2692 for (Partition &part : partitions)
2693 for (PhdrEntry *p : part.phdrs)
2694 if (p->p_type == PT_LOAD && (p->p_flags & PF_X))
2695 lastRX = p;
2696
2697 // Layout SHF_ALLOC sections before non-SHF_ALLOC sections. A non-SHF_ALLOC
2698 // will not occupy file offsets contained by a PT_LOAD.
2699 for (OutputSection *sec : outputSections) {
2700 if (!(sec->flags & SHF_ALLOC))
2701 continue;
2702 off = setFileOffset(sec, off);
2703
2704 // If this is a last section of the last executable segment and that
2705 // segment is the last loadable segment, align the offset of the
2706 // following section to avoid loading non-segments parts of the file.
2707 if (config->zSeparate != SeparateSegmentKind::None && lastRX &&
2708 lastRX->lastSec == sec)
2709 off = alignTo(off, config->commonPageSize);
2710 }
2711 for (OutputSection *sec : outputSections)
2712 if (!(sec->flags & SHF_ALLOC))
2713 off = setFileOffset(sec, off);
2714
2715 sectionHeaderOff = alignTo(off, config->wordsize);
2716 fileSize = sectionHeaderOff + (outputSections.size() + 1) * sizeof(Elf_Shdr);
2717
2718 // Our logic assumes that sections have rising VA within the same segment.
2719 // With use of linker scripts it is possible to violate this rule and get file
2720 // offset overlaps or overflows. That should never happen with a valid script
2721 // which does not move the location counter backwards and usually scripts do
2722 // not do that. Unfortunately, there are apps in the wild, for example, Linux
2723 // kernel, which control segment distribution explicitly and move the counter
2724 // backwards, so we have to allow doing that to support linking them. We
2725 // perform non-critical checks for overlaps in checkSectionOverlap(), but here
2726 // we want to prevent file size overflows because it would crash the linker.
2727 for (OutputSection *sec : outputSections) {
2728 if (sec->type == SHT_NOBITS)
2729 continue;
2730 if ((sec->offset > fileSize) || (sec->offset + sec->size > fileSize))
2731 error("unable to place section " + sec->name + " at file offset " +
2732 rangeToString(sec->offset, sec->size) +
2733 "; check your linker script for overflows");
2734 }
2735}
2736
2737// Finalize the program headers. We call this function after we assign
2738// file offsets and VAs to all sections.
2739template <class ELFT> void Writer<ELFT>::setPhdrs(Partition &part) {
2740 for (PhdrEntry *p : part.phdrs) {
2741 OutputSection *first = p->firstSec;
2742 OutputSection *last = p->lastSec;
2743
2744 if (first) {
2745 p->p_filesz = last->offset - first->offset;
2746 if (last->type != SHT_NOBITS)
2747 p->p_filesz += last->size;
2748
2749 p->p_memsz = last->addr + last->size - first->addr;
2750 p->p_offset = first->offset;
2751 p->p_vaddr = first->addr;
2752
2753 // File offsets in partitions other than the main partition are relative
2754 // to the offset of the ELF headers. Perform that adjustment now.
2755 if (part.elfHeader)
2756 p->p_offset -= part.elfHeader->getParent()->offset;
2757
2758 if (!p->hasLMA)
2759 p->p_paddr = first->getLMA();
2760 }
2761
2762 if (p->p_type == PT_GNU_RELRO) {
2763 p->p_align = 1;
2764 // musl/glibc ld.so rounds the size down, so we need to round up
2765 // to protect the last page. This is a no-op on FreeBSD which always
2766 // rounds up.
2767 p->p_memsz = alignTo(p->p_offset + p->p_memsz, config->commonPageSize) -
2768 p->p_offset;
2769 }
2770 }
2771}
2772
2773// A helper struct for checkSectionOverlap.
2774namespace {
2775struct SectionOffset {
2776 OutputSection *sec;
2777 uint64_t offset;
2778};
2779} // namespace
2780
2781// Check whether sections overlap for a specific address range (file offsets,
2782// load and virtual addresses).
2783static void checkOverlap(StringRef name, std::vector<SectionOffset> &sections,
2784 bool isVirtualAddr) {
2785 llvm::sort(sections, [=](const SectionOffset &a, const SectionOffset &b) {
2786 return a.offset < b.offset;
2787 });
2788
2789 // Finding overlap is easy given a vector is sorted by start position.
2790 // If an element starts before the end of the previous element, they overlap.
2791 for (size_t i = 1, end = sections.size(); i < end; ++i) {
2792 SectionOffset a = sections[i - 1];
2793 SectionOffset b = sections[i];
2794 if (b.offset >= a.offset + a.sec->size)
2795 continue;
2796
2797 // If both sections are in OVERLAY we allow the overlapping of virtual
2798 // addresses, because it is what OVERLAY was designed for.
2799 if (isVirtualAddr && a.sec->inOverlay && b.sec->inOverlay)
2800 continue;
2801
2802 errorOrWarn("section " + a.sec->name + " " + name +
2803 " range overlaps with " + b.sec->name + "\n>>> " + a.sec->name +
2804 " range is " + rangeToString(a.offset, a.sec->size) + "\n>>> " +
2805 b.sec->name + " range is " +
2806 rangeToString(b.offset, b.sec->size));
2807 }
2808}
2809
2810// Check for overlapping sections and address overflows.
2811//
2812// In this function we check that none of the output sections have overlapping
2813// file offsets. For SHF_ALLOC sections we also check that the load address
2814// ranges and the virtual address ranges don't overlap
2815template <class ELFT> void Writer<ELFT>::checkSections() {
2816 // First, check that section's VAs fit in available address space for target.
2817 for (OutputSection *os : outputSections)
2818 if ((os->addr + os->size < os->addr) ||
2819 (!ELFT::Is64Bits && os->addr + os->size > UINT32_MAX0xffffffffU))
2820 errorOrWarn("section " + os->name + " at 0x" + utohexstr(os->addr) +
2821 " of size 0x" + utohexstr(os->size) +
2822 " exceeds available address space");
2823
2824 // Check for overlapping file offsets. In this case we need to skip any
2825 // section marked as SHT_NOBITS. These sections don't actually occupy space in
2826 // the file so Sec->Offset + Sec->Size can overlap with others. If --oformat
2827 // binary is specified only add SHF_ALLOC sections are added to the output
2828 // file so we skip any non-allocated sections in that case.
2829 std::vector<SectionOffset> fileOffs;
2830 for (OutputSection *sec : outputSections)
2831 if (sec->size > 0 && sec->type != SHT_NOBITS &&
2832 (!config->oFormatBinary || (sec->flags & SHF_ALLOC)))
2833 fileOffs.push_back({sec, sec->offset});
2834 checkOverlap("file", fileOffs, false);
2835
2836 // When linking with -r there is no need to check for overlapping virtual/load
2837 // addresses since those addresses will only be assigned when the final
2838 // executable/shared object is created.
2839 if (config->relocatable)
2840 return;
2841
2842 // Checking for overlapping virtual and load addresses only needs to take
2843 // into account SHF_ALLOC sections since others will not be loaded.
2844 // Furthermore, we also need to skip SHF_TLS sections since these will be
2845 // mapped to other addresses at runtime and can therefore have overlapping
2846 // ranges in the file.
2847 std::vector<SectionOffset> vmas;
2848 for (OutputSection *sec : outputSections)
2849 if (sec->size > 0 && (sec->flags & SHF_ALLOC) && !(sec->flags & SHF_TLS))
2850 vmas.push_back({sec, sec->addr});
2851 checkOverlap("virtual address", vmas, true);
2852
2853 // Finally, check that the load addresses don't overlap. This will usually be
2854 // the same as the virtual addresses but can be different when using a linker
2855 // script with AT().
2856 std::vector<SectionOffset> lmas;
2857 for (OutputSection *sec : outputSections)
2858 if (sec->size > 0 && (sec->flags & SHF_ALLOC) && !(sec->flags & SHF_TLS))
2859 lmas.push_back({sec, sec->getLMA()});
2860 checkOverlap("load address", lmas, false);
2861}
2862
2863// The entry point address is chosen in the following ways.
2864//
2865// 1. the '-e' entry command-line option;
2866// 2. the ENTRY(symbol) command in a linker control script;
2867// 3. the value of the symbol _start, if present;
2868// 4. the number represented by the entry symbol, if it is a number;
2869// 5. the address of the first byte of the .text section, if present;
2870// 6. the address 0.
2871static uint64_t getEntryAddr() {
2872 // Case 1, 2 or 3
2873 if (Symbol *b = symtab->find(config->entry))
2874 return b->getVA();
2875
2876 // Case 4
2877 uint64_t addr;
2878 if (to_integer(config->entry, addr))
2879 return addr;
2880
2881 // Case 5
2882 if (OutputSection *sec = findSection(".text")) {
2883 if (config->warnMissingEntry)
2884 warn("cannot find entry symbol " + config->entry + "; defaulting to 0x" +
2885 utohexstr(sec->addr));
2886 return sec->addr;
2887 }
2888
2889 // Case 6
2890 if (config->warnMissingEntry)
2891 warn("cannot find entry symbol " + config->entry +
2892 "; not setting start address");
2893 return 0;
2894}
2895
2896static uint16_t getELFType() {
2897 if (config->isPic)
2898 return ET_DYN;
2899 if (config->relocatable)
2900 return ET_REL;
2901 return ET_EXEC;
2902}
2903
2904template <class ELFT> void Writer<ELFT>::writeHeader() {
2905 writeEhdr<ELFT>(Out::bufferStart, *mainPart);
2906 writePhdrs<ELFT>(Out::bufferStart + sizeof(Elf_Ehdr), *mainPart);
2907
2908 auto *eHdr = reinterpret_cast<Elf_Ehdr *>(Out::bufferStart);
2909 eHdr->e_type = getELFType();
2910 eHdr->e_entry = getEntryAddr();
2911 eHdr->e_shoff = sectionHeaderOff;
2912
2913 // Write the section header table.
2914 //
2915 // The ELF header can only store numbers up to SHN_LORESERVE in the e_shnum
2916 // and e_shstrndx fields. When the value of one of these fields exceeds
2917 // SHN_LORESERVE ELF requires us to put sentinel values in the ELF header and
2918 // use fields in the section header at index 0 to store
2919 // the value. The sentinel values and fields are:
2920 // e_shnum = 0, SHdrs[0].sh_size = number of sections.
2921 // e_shstrndx = SHN_XINDEX, SHdrs[0].sh_link = .shstrtab section index.
2922 auto *sHdrs = reinterpret_cast<Elf_Shdr *>(Out::bufferStart + eHdr->e_shoff);
2923 size_t num = outputSections.size() + 1;
2924 if (num >= SHN_LORESERVE)
2925 sHdrs->sh_size = num;
2926 else
2927 eHdr->e_shnum = num;
2928
2929 uint32_t strTabIndex = in.shStrTab->getParent()->sectionIndex;
2930 if (strTabIndex >= SHN_LORESERVE) {
2931 sHdrs->sh_link = strTabIndex;
2932 eHdr->e_shstrndx = SHN_XINDEX;
2933 } else {
2934 eHdr->e_shstrndx = strTabIndex;
2935 }
2936
2937 for (OutputSection *sec : outputSections)
2938 sec->writeHeaderTo<ELFT>(++sHdrs);
2939}
2940
2941// Open a result file.
2942template <class ELFT> void Writer<ELFT>::openFile() {
2943 uint64_t maxSize = config->is64 ? INT64_MAX0x7fffffffffffffffLL : UINT32_MAX0xffffffffU;
2944 if (fileSize != size_t(fileSize) || maxSize < fileSize) {
2945 std::string msg;
2946 raw_string_ostream s(msg);
2947 s << "output file too large: " << Twine(fileSize) << " bytes\n"
2948 << "section sizes:\n";
2949 for (OutputSection *os : outputSections)
2950 s << os->name << ' ' << os->size << "\n";
2951 error(s.str());
2952 return;
2953 }
2954
2955 unlinkAsync(config->outputFile);
2956 unsigned flags = 0;
2957 if (!config->relocatable)
2958 flags |= FileOutputBuffer::F_executable;
2959 if (!config->mmapOutputFile)
2960 flags |= FileOutputBuffer::F_no_mmap;
2961 Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
2962 FileOutputBuffer::create(config->outputFile, fileSize, flags);
2963
2964 if (!bufferOrErr) {
2965 error("failed to open " + config->outputFile + ": " +
2966 llvm::toString(bufferOrErr.takeError()));
2967 return;
2968 }
2969 buffer = std::move(*bufferOrErr);
2970 Out::bufferStart = buffer->getBufferStart();
2971}
2972
2973template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
2974 for (OutputSection *sec : outputSections)
2975 if (sec->flags & SHF_ALLOC)
2976 sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
2977}
2978
2979static void fillTrap(uint8_t *i, uint8_t *end) {
2980 for (; i + 4 <= end; i += 4)
2981 memcpy(i, &target->trapInstr, 4);
2982}
2983
2984// Fill the last page of executable segments with trap instructions
2985// instead of leaving them as zero. Even though it is not required by any
2986// standard, it is in general a good thing to do for security reasons.
2987//
2988// We'll leave other pages in segments as-is because the rest will be
2989// overwritten by output sections.
2990template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
2991 for (Partition &part : partitions) {
2992 // Fill the last page.
2993 for (PhdrEntry *p : part.phdrs)
2994 if (p->p_type == PT_LOAD && (p->p_flags & PF_X))
2995 fillTrap(Out::bufferStart + alignDown(p->firstSec->offset + p->p_filesz,
2996 config->commonPageSize),
2997 Out::bufferStart + alignTo(p->firstSec->offset + p->p_filesz,
2998 config->commonPageSize));
2999
3000 // Round up the file size of the last segment to the page boundary iff it is
3001 // an executable segment to ensure that other tools don't accidentally
3002 // trim the instruction padding (e.g. when stripping the file).
3003 PhdrEntry *last = nullptr;
3004 for (PhdrEntry *p : part.phdrs)
3005 if (p->p_type == PT_LOAD)
3006 last = p;
3007
3008 if (last && (last->p_flags & PF_X))
3009 last->p_memsz = last->p_filesz =
3010 alignTo(last->p_filesz, config->commonPageSize);
3011 }
3012}
3013
3014// Write section contents to a mmap'ed file.
3015template <class ELFT> void Writer<ELFT>::writeSections() {
3016 // In -r or -emit-relocs mode, write the relocation sections first as in
3017 // ELf_Rel targets we might find out that we need to modify the relocated
3018 // section while doing it.
3019 for (OutputSection *sec : outputSections)
3020 if (sec->type == SHT_REL || sec->type == SHT_RELA)
3021 sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
3022
3023 for (OutputSection *sec : outputSections)
3024 if (sec->type != SHT_REL && sec->type != SHT_RELA)
3025 sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
3026
3027 // Finally, check that all dynamic relocation addends were written correctly.
3028 if (config->checkDynamicRelocs && config->writeAddends) {
3029 for (OutputSection *sec : outputSections)
3030 if (sec->type == SHT_REL || sec->type == SHT_RELA)
3031 sec->checkDynRelAddends(Out::bufferStart);
3032 }
3033}
3034
3035// Computes a hash value of Data using a given hash function.
3036// In order to utilize multiple cores, we first split data into 1MB
3037// chunks, compute a hash for each chunk, and then compute a hash value
3038// of the hash values.
3039static void
3040computeHash(llvm::MutableArrayRef<uint8_t> hashBuf,
3041 llvm::ArrayRef<uint8_t> data,
3042 std::function<void(uint8_t *dest, ArrayRef<uint8_t> arr)> hashFn) {
3043 std::vector<ArrayRef<uint8_t>> chunks = split(data, 1024 * 1024);
3044 std::vector<uint8_t> hashes(chunks.size() * hashBuf.size());
3045
3046 // Compute hash values.
3047 parallelForEachN(0, chunks.size(), [&](size_t i) {
3048 hashFn(hashes.data() + i * hashBuf.size(), chunks[i]);
3049 });
3050
3051 // Write to the final output buffer.
3052 hashFn(hashBuf.data(), hashes);
3053}
3054
3055template <class ELFT> void Writer<ELFT>::writeBuildId() {
3056 if (!mainPart->buildId || !mainPart->buildId->getParent())
3057 return;
3058
3059 if (config->buildId == BuildIdKind::Hexstring) {
3060 for (Partition &part : partitions)
3061 part.buildId->writeBuildId(config->buildIdVector);
3062 return;
3063 }
3064
3065 // Compute a hash of all sections of the output file.
3066 size_t hashSize = mainPart->buildId->hashSize;
3067 std::vector<uint8_t> buildId(hashSize);
3068 llvm::ArrayRef<uint8_t> buf{Out::bufferStart, size_t(fileSize)};
3069
3070 switch (config->buildId) {
3071 case BuildIdKind::Fast:
3072 computeHash(buildId, buf, [](uint8_t *dest, ArrayRef<uint8_t> arr) {
3073 write64le(dest, xxHash64(arr));
3074 });
3075 break;
3076 case BuildIdKind::Md5:
3077 computeHash(buildId, buf, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
3078 memcpy(dest, MD5::hash(arr).data(), hashSize);
3079 });
3080 break;
3081 case BuildIdKind::Sha1:
3082 computeHash(buildId, buf, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
3083 memcpy(dest, SHA1::hash(arr).data(), hashSize);
3084 });
3085 break;
3086 case BuildIdKind::Uuid:
3087 if (auto ec = llvm::getRandomBytes(buildId.data(), hashSize))
3088 error("entropy source failure: " + ec.message());
3089 break;
3090 default:
3091 llvm_unreachable("unknown BuildIdKind")__builtin_unreachable();
3092 }
3093 for (Partition &part : partitions)
3094 part.buildId->writeBuildId(buildId);
3095}
3096
3097template void elf::createSyntheticSections<ELF32LE>();
3098template void elf::createSyntheticSections<ELF32BE>();
3099template void elf::createSyntheticSections<ELF64LE>();
3100template void elf::createSyntheticSections<ELF64BE>();
3101
3102template void elf::writeResult<ELF32LE>();
3103template void elf::writeResult<ELF32BE>();
3104template void elf::writeResult<ELF64LE>();
3105template void elf::writeResult<ELF64BE>();

/usr/include/c++/v1/__algorithm/stable_partition.h

1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___ALGORITHM_STABLE_PARTITION_H
10#define _LIBCPP___ALGORITHM_STABLE_PARTITION_H
11
12#include <__config>
13#include <__algorithm/rotate.h>
14#include <__iterator/iterator_traits.h>
15#include <__utility/swap.h>
16#include <memory>
17
18#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
19#pragma GCC system_header
20#endif
21
22_LIBCPP_PUSH_MACROSpush_macro("min") push_macro("max")
23#include <__undef_macros>
24
25_LIBCPP_BEGIN_NAMESPACE_STDnamespace std { inline namespace __1 {
26
27template <class _Predicate, class _ForwardIterator, class _Distance, class _Pair>
28_ForwardIterator
29__stable_partition(_ForwardIterator __first, _ForwardIterator __last, _Predicate __pred,
30 _Distance __len, _Pair __p, forward_iterator_tag __fit)
31{
32 // *__first is known to be false
33 // __len >= 1
34 if (__len == 1)
35 return __first;
36 if (__len == 2)
37 {
38 _ForwardIterator __m = __first;
39 if (__pred(*++__m))
40 {
41 swap(*__first, *__m);
42 return __m;
43 }
44 return __first;
45 }
46 if (__len <= __p.second)
47 { // The buffer is big enough to use
48 typedef typename iterator_traits<_ForwardIterator>::value_type value_type;
49 __destruct_n __d(0);
50 unique_ptr<value_type, __destruct_n&> __h(__p.first, __d);
51 // Move the falses into the temporary buffer, and the trues to the front of the line
52 // Update __first to always point to the end of the trues
53 value_type* __t = __p.first;
54 ::new ((void*)__t) value_type(_VSTDstd::__1::move(*__first));
55 __d.template __incr<value_type>();
56 ++__t;
57 _ForwardIterator __i = __first;
58 while (++__i != __last)
59 {
60 if (__pred(*__i))
61 {
62 *__first = _VSTDstd::__1::move(*__i);
63 ++__first;
64 }
65 else
66 {
67 ::new ((void*)__t) value_type(_VSTDstd::__1::move(*__i));
68 __d.template __incr<value_type>();
69 ++__t;
70 }
71 }
72 // All trues now at start of range, all falses in buffer
73 // Move falses back into range, but don't mess up __first which points to first false
74 __i = __first;
75 for (value_type* __t2 = __p.first; __t2 < __t; ++__t2, (void) ++__i)
76 *__i = _VSTDstd::__1::move(*__t2);
77 // __h destructs moved-from values out of the temp buffer, but doesn't deallocate buffer
78 return __first;
79 }
80 // Else not enough buffer, do in place
81 // __len >= 3
82 _ForwardIterator __m = __first;
83 _Distance __len2 = __len / 2; // __len2 >= 2
84 _VSTDstd::__1::advance(__m, __len2);
85 // recurse on [__first, __m), *__first know to be false
86 // F?????????????????
87 // f m l
88 typedef typename add_lvalue_reference<_Predicate>::type _PredRef;
89 _ForwardIterator __first_false = _VSTDstd::__1::__stable_partition<_PredRef>(__first, __m, __pred, __len2, __p, __fit);
90 // TTTFFFFF??????????
91 // f ff m l
92 // recurse on [__m, __last], except increase __m until *(__m) is false, *__last know to be true
93 _ForwardIterator __m1 = __m;
94 _ForwardIterator __second_false = __last;
95 _Distance __len_half = __len - __len2;
96 while (__pred(*__m1))
97 {
98 if (++__m1 == __last)
99 goto __second_half_done;
100 --__len_half;
101 }
102 // TTTFFFFFTTTF??????
103 // f ff m m1 l
104 __second_false = _VSTDstd::__1::__stable_partition<_PredRef>(__m1, __last, __pred, __len_half, __p, __fit);
105__second_half_done:
106 // TTTFFFFFTTTTTFFFFF
107 // f ff m sf l
108 return _VSTDstd::__1::rotate(__first_false, __m, __second_false);
109 // TTTTTTTTFFFFFFFFFF
110 // |
111}
112
113template <class _Predicate, class _ForwardIterator>
114_ForwardIterator
115__stable_partition(_ForwardIterator __first, _ForwardIterator __last, _Predicate __pred,
116 forward_iterator_tag)
117{
118 const unsigned __alloc_limit = 3; // might want to make this a function of trivial assignment
119 // Either prove all true and return __first or point to first false
120 while (true)
121 {
122 if (__first == __last)
123 return __first;
124 if (!__pred(*__first))
125 break;
126 ++__first;
127 }
128 // We now have a reduced range [__first, __last)
129 // *__first is known to be false
130 typedef typename iterator_traits<_ForwardIterator>::difference_type difference_type;
131 typedef typename iterator_traits<_ForwardIterator>::value_type value_type;
132 difference_type __len = _VSTDstd::__1::distance(__first, __last);
133 pair<value_type*, ptrdiff_t> __p(0, 0);
134 unique_ptr<value_type, __return_temporary_buffer> __h;
135 if (__len >= __alloc_limit)
136 {
137 __p = _VSTDstd::__1::get_temporary_buffer<value_type>(__len);
138 __h.reset(__p.first);
139 }
140 return _VSTDstd::__1::__stable_partition<typename add_lvalue_reference<_Predicate>::type>
141 (__first, __last, __pred, __len, __p, forward_iterator_tag());
142}
143
144template <class _Predicate, class _BidirectionalIterator, class _Distance, class _Pair>
145_BidirectionalIterator
146__stable_partition(_BidirectionalIterator __first, _BidirectionalIterator __last, _Predicate __pred,
147 _Distance __len, _Pair __p, bidirectional_iterator_tag __bit)
148{
149 // *__first is known to be false
150 // *__last is known to be true
151 // __len >= 2
152 if (__len == 2)
153 {
154 swap(*__first, *__last);
155 return __last;
156 }
157 if (__len == 3)
158 {
159 _BidirectionalIterator __m = __first;
160 if (__pred(*++__m))
161 {
162 swap(*__first, *__m);
163 swap(*__m, *__last);
164 return __last;
165 }
166 swap(*__m, *__last);
167 swap(*__first, *__m);
168 return __m;
169 }
170 if (__len <= __p.second)
171 { // The buffer is big enough to use
172 typedef typename iterator_traits<_BidirectionalIterator>::value_type value_type;
173 __destruct_n __d(0);
174 unique_ptr<value_type, __destruct_n&> __h(__p.first, __d);
175 // Move the falses into the temporary buffer, and the trues to the front of the line
176 // Update __first to always point to the end of the trues
177 value_type* __t = __p.first;
178 ::new ((void*)__t) value_type(_VSTDstd::__1::move(*__first));
179 __d.template __incr<value_type>();
180 ++__t;
181 _BidirectionalIterator __i = __first;
182 while (++__i != __last)
183 {
184 if (__pred(*__i))
185 {
186 *__first = _VSTDstd::__1::move(*__i);
187 ++__first;
188 }
189 else
190 {
191 ::new ((void*)__t) value_type(_VSTDstd::__1::move(*__i));
192 __d.template __incr<value_type>();
193 ++__t;
194 }
195 }
196 // move *__last, known to be true
197 *__first = _VSTDstd::__1::move(*__i);
198 __i = ++__first;
199 // All trues now at start of range, all falses in buffer
200 // Move falses back into range, but don't mess up __first which points to first false
201 for (value_type* __t2 = __p.first; __t2 < __t; ++__t2, (void) ++__i)
202 *__i = _VSTDstd::__1::move(*__t2);
203 // __h destructs moved-from values out of the temp buffer, but doesn't deallocate buffer
204 return __first;
205 }
206 // Else not enough buffer, do in place
207 // __len >= 4
208 _BidirectionalIterator __m = __first;
209 _Distance __len2 = __len / 2; // __len2 >= 2
210 _VSTDstd::__1::advance(__m, __len2);
211 // recurse on [__first, __m-1], except reduce __m-1 until *(__m-1) is true, *__first know to be false
212 // F????????????????T
213 // f m l
214 _BidirectionalIterator __m1 = __m;
215 _BidirectionalIterator __first_false = __first;
216 _Distance __len_half = __len2;
217 while (!__pred(*--__m1))
218 {
219 if (__m1 == __first)
220 goto __first_half_done;
221 --__len_half;
222 }
223 // F???TFFF?????????T
224 // f m1 m l
225 typedef typename add_lvalue_reference<_Predicate>::type _PredRef;
226 __first_false = _VSTDstd::__1::__stable_partition<_PredRef>(__first, __m1, __pred, __len_half, __p, __bit);
227__first_half_done:
228 // TTTFFFFF?????????T
229 // f ff m l
230 // recurse on [__m, __last], except increase __m until *(__m) is false, *__last know to be true
231 __m1 = __m;
232 _BidirectionalIterator __second_false = __last;
233 ++__second_false;
234 __len_half = __len - __len2;
235 while (__pred(*__m1))
236 {
237 if (++__m1 == __last)
238 goto __second_half_done;
239 --__len_half;
240 }
241 // TTTFFFFFTTTF?????T
242 // f ff m m1 l
243 __second_false = _VSTDstd::__1::__stable_partition<_PredRef>(__m1, __last, __pred, __len_half, __p, __bit);
244__second_half_done:
245 // TTTFFFFFTTTTTFFFFF
246 // f ff m sf l
247 return _VSTDstd::__1::rotate(__first_false, __m, __second_false);
248 // TTTTTTTTFFFFFFFFFF
249 // |
250}
251
252template <class _Predicate, class _BidirectionalIterator>
253_BidirectionalIterator
254__stable_partition(_BidirectionalIterator __first, _BidirectionalIterator __last, _Predicate __pred,
255 bidirectional_iterator_tag)
256{
257 typedef typename iterator_traits<_BidirectionalIterator>::difference_type difference_type;
258 typedef typename iterator_traits<_BidirectionalIterator>::value_type value_type;
259 const difference_type __alloc_limit = 4; // might want to make this a function of trivial assignment
260 // Either prove all true and return __first or point to first false
261 while (true)
22
Loop condition is true. Entering loop body
262 {
263 if (__first == __last)
23
Taking false branch
264 return __first;
265 if (!__pred(*__first))
24
Calling 'operator()'
266 break;
267 ++__first;
268 }
269 // __first points to first false, everything prior to __first is already set.
270 // Either prove [__first, __last) is all false and return __first, or point __last to last true
271 do
272 {
273 if (__first == --__last)
274 return __first;
275 } while (!__pred(*__last));
276 // We now have a reduced range [__first, __last]
277 // *__first is known to be false
278 // *__last is known to be true
279 // __len >= 2
280 difference_type __len = _VSTDstd::__1::distance(__first, __last) + 1;
281 pair<value_type*, ptrdiff_t> __p(0, 0);
282 unique_ptr<value_type, __return_temporary_buffer> __h;
283 if (__len >= __alloc_limit)
284 {
285 __p = _VSTDstd::__1::get_temporary_buffer<value_type>(__len);
286 __h.reset(__p.first);
287 }
288 return _VSTDstd::__1::__stable_partition<typename add_lvalue_reference<_Predicate>::type>
289 (__first, __last, __pred, __len, __p, bidirectional_iterator_tag());
290}
291
292template <class _ForwardIterator, class _Predicate>
293inline _LIBCPP_INLINE_VISIBILITY__attribute__ ((__visibility__("hidden"))) __attribute__ ((__exclude_from_explicit_instantiation__
))
294_ForwardIterator
295stable_partition(_ForwardIterator __first, _ForwardIterator __last, _Predicate __pred)
296{
297 return _VSTDstd::__1::__stable_partition<typename add_lvalue_reference<_Predicate>::type>
21
Calling '__stable_partition<(lambda at /usr/src/gnu/usr.bin/clang/liblldELF/../../../llvm/lld/ELF/Writer.cpp:1912:35) &, std::__wrap_iter<lld::elf::InputSectionBase **>>'
298 (__first, __last, __pred, typename iterator_traits<_ForwardIterator>::iterator_category());
299}
300
301_LIBCPP_END_NAMESPACE_STD} }
302
303_LIBCPP_POP_MACROSpop_macro("min") pop_macro("max")
304
305#endif // _LIBCPP___ALGORITHM_STABLE_PARTITION_H