1 //===- LinkerScript.cpp ---------------------------------------------------===//
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains the parser/evaluator of the linker script.
12 //===----------------------------------------------------------------------===//
14 #include "LinkerScript.h"
16 #include "InputSection.h"
18 #include "OutputSections.h"
20 #include "SymbolTable.h"
22 #include "SyntheticSections.h"
26 #include "llvm/ADT/STLExtras.h"
27 #include "llvm/ADT/StringRef.h"
28 #include "llvm/Support/Casting.h"
29 #include "llvm/Support/Compression.h"
30 #include "llvm/Support/ELF.h"
31 #include "llvm/Support/Endian.h"
32 #include "llvm/Support/ErrorHandling.h"
33 #include "llvm/Support/FileSystem.h"
34 #include "llvm/Support/Path.h"
45 using namespace llvm::ELF;
46 using namespace llvm::object;
47 using namespace llvm::support::endian;
49 using namespace lld::elf;
51 LinkerScript *elf::Script;
53 uint64_t ExprValue::getValue() const {
55 if (OutputSection *OS = Sec->getOutputSection())
56 return alignTo(Sec->getOffset(Val) + OS->Addr, Alignment);
57 error("unable to evaluate expression: input section " + Sec->Name +
58 " has no output section assigned");
60 return alignTo(Val, Alignment);
63 uint64_t ExprValue::getSecAddr() const {
65 return Sec->getOffset(0) + Sec->getOutputSection()->Addr;
69 template <class ELFT> static SymbolBody *addRegular(SymbolAssignment *Cmd) {
71 uint8_t Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT;
72 std::tie(Sym, std::ignore) = Symtab<ELFT>::X->insert(
73 Cmd->Name, /*Type*/ 0, Visibility, /*CanOmitFromDynSym*/ false,
75 Sym->Binding = STB_GLOBAL;
76 ExprValue Value = Cmd->Expression();
77 SectionBase *Sec = Value.isAbsolute() ? nullptr : Value.Sec;
79 // We want to set symbol values early if we can. This allows us to use symbols
80 // as variables in linker scripts. Doing so allows us to write expressions
81 // like this: `alignment = 16; . = ALIGN(., alignment)`
82 uint64_t SymValue = Value.isAbsolute() ? Value.getValue() : 0;
83 replaceBody<DefinedRegular>(Sym, Cmd->Name, /*IsLocal=*/false, Visibility,
84 STT_NOTYPE, SymValue, 0, Sec, nullptr);
88 OutputSectionCommand *
89 LinkerScript::createOutputSectionCommand(StringRef Name, StringRef Location) {
90 OutputSectionCommand *&CmdRef = NameToOutputSectionCommand[Name];
91 OutputSectionCommand *Cmd;
92 if (CmdRef && CmdRef->Location.empty()) {
93 // There was a forward reference.
96 Cmd = make<OutputSectionCommand>(Name);
100 Cmd->Location = Location;
104 OutputSectionCommand *
105 LinkerScript::getOrCreateOutputSectionCommand(StringRef Name) {
106 OutputSectionCommand *&CmdRef = NameToOutputSectionCommand[Name];
108 CmdRef = make<OutputSectionCommand>(Name);
112 void LinkerScript::setDot(Expr E, const Twine &Loc, bool InSec) {
113 uint64_t Val = E().getValue();
116 error(Loc + ": unable to move location counter backward for: " +
119 error(Loc + ": unable to move location counter backward");
122 // Update to location counter means update to section size.
124 CurOutSec->Size = Dot - CurOutSec->Addr;
127 // Sets value of a symbol. Two kinds of symbols are processed: synthetic
128 // symbols, whose value is an offset from beginning of section and regular
129 // symbols whose value is absolute.
130 void LinkerScript::assignSymbol(SymbolAssignment *Cmd, bool InSec) {
131 if (Cmd->Name == ".") {
132 setDot(Cmd->Expression, Cmd->Location, InSec);
139 auto *Sym = cast<DefinedRegular>(Cmd->Sym);
140 ExprValue V = Cmd->Expression();
141 if (V.isAbsolute()) {
142 Sym->Value = V.getValue();
144 Sym->Section = V.Sec;
145 if (Sym->Section->Flags & SHF_ALLOC)
146 Sym->Value = alignTo(V.Val, V.Alignment);
148 Sym->Value = V.getValue();
152 static SymbolBody *findSymbol(StringRef S) {
153 switch (Config->EKind) {
155 return Symtab<ELF32LE>::X->find(S);
157 return Symtab<ELF32BE>::X->find(S);
159 return Symtab<ELF64LE>::X->find(S);
161 return Symtab<ELF64BE>::X->find(S);
163 llvm_unreachable("unknown Config->EKind");
167 static SymbolBody *addRegularSymbol(SymbolAssignment *Cmd) {
168 switch (Config->EKind) {
170 return addRegular<ELF32LE>(Cmd);
172 return addRegular<ELF32BE>(Cmd);
174 return addRegular<ELF64LE>(Cmd);
176 return addRegular<ELF64BE>(Cmd);
178 llvm_unreachable("unknown Config->EKind");
182 void LinkerScript::addSymbol(SymbolAssignment *Cmd) {
183 if (Cmd->Name == ".")
186 // If a symbol was in PROVIDE(), we need to define it only when
187 // it is a referenced undefined symbol.
188 SymbolBody *B = findSymbol(Cmd->Name);
189 if (Cmd->Provide && (!B || B->isDefined()))
192 Cmd->Sym = addRegularSymbol(Cmd);
195 bool SymbolAssignment::classof(const BaseCommand *C) {
196 return C->Kind == AssignmentKind;
199 bool OutputSectionCommand::classof(const BaseCommand *C) {
200 return C->Kind == OutputSectionKind;
203 // Fill [Buf, Buf + Size) with Filler.
204 // This is used for linker script "=fillexp" command.
205 static void fill(uint8_t *Buf, size_t Size, uint32_t Filler) {
207 for (; I + 4 < Size; I += 4)
208 memcpy(Buf + I, &Filler, 4);
209 memcpy(Buf + I, &Filler, Size - I);
212 bool InputSectionDescription::classof(const BaseCommand *C) {
213 return C->Kind == InputSectionKind;
216 bool AssertCommand::classof(const BaseCommand *C) {
217 return C->Kind == AssertKind;
220 bool BytesDataCommand::classof(const BaseCommand *C) {
221 return C->Kind == BytesDataKind;
224 static StringRef basename(InputSectionBase *S) {
226 return sys::path::filename(S->File->getName());
230 bool LinkerScript::shouldKeep(InputSectionBase *S) {
231 for (InputSectionDescription *ID : Opt.KeptSections)
232 if (ID->FilePat.match(basename(S)))
233 for (SectionPattern &P : ID->SectionPatterns)
234 if (P.SectionPat.match(S->Name))
239 // A helper function for the SORT() command.
240 static std::function<bool(InputSectionBase *, InputSectionBase *)>
241 getComparator(SortSectionPolicy K) {
243 case SortSectionPolicy::Alignment:
244 return [](InputSectionBase *A, InputSectionBase *B) {
245 // ">" is not a mistake. Sections with larger alignments are placed
246 // before sections with smaller alignments in order to reduce the
247 // amount of padding necessary. This is compatible with GNU.
248 return A->Alignment > B->Alignment;
250 case SortSectionPolicy::Name:
251 return [](InputSectionBase *A, InputSectionBase *B) {
252 return A->Name < B->Name;
254 case SortSectionPolicy::Priority:
255 return [](InputSectionBase *A, InputSectionBase *B) {
256 return getPriority(A->Name) < getPriority(B->Name);
259 llvm_unreachable("unknown sort policy");
263 // A helper function for the SORT() command.
264 static bool matchConstraints(ArrayRef<InputSectionBase *> Sections,
265 ConstraintKind Kind) {
266 if (Kind == ConstraintKind::NoConstraint)
269 bool IsRW = llvm::any_of(Sections, [](InputSectionBase *Sec) {
270 return static_cast<InputSectionBase *>(Sec)->Flags & SHF_WRITE;
273 return (IsRW && Kind == ConstraintKind::ReadWrite) ||
274 (!IsRW && Kind == ConstraintKind::ReadOnly);
277 static void sortSections(InputSection **Begin, InputSection **End,
278 SortSectionPolicy K) {
279 if (K != SortSectionPolicy::Default && K != SortSectionPolicy::None)
280 std::stable_sort(Begin, End, getComparator(K));
283 // Compute and remember which sections the InputSectionDescription matches.
284 std::vector<InputSection *>
285 LinkerScript::computeInputSections(const InputSectionDescription *Cmd) {
286 std::vector<InputSection *> Ret;
288 // Collects all sections that satisfy constraints of Cmd.
289 for (const SectionPattern &Pat : Cmd->SectionPatterns) {
290 size_t SizeBefore = Ret.size();
292 for (InputSectionBase *Sec : InputSections) {
297 reportDiscarded(Sec);
301 // For -emit-relocs we have to ignore entries like
302 // .rela.dyn : { *(.rela.data) }
303 // which are common because they are in the default bfd script.
304 if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
307 StringRef Filename = basename(Sec);
308 if (!Cmd->FilePat.match(Filename) ||
309 Pat.ExcludedFilePat.match(Filename) ||
310 !Pat.SectionPat.match(Sec->Name))
313 Ret.push_back(cast<InputSection>(Sec));
314 Sec->Assigned = true;
317 // Sort sections as instructed by SORT-family commands and --sort-section
318 // option. Because SORT-family commands can be nested at most two depth
319 // (e.g. SORT_BY_NAME(SORT_BY_ALIGNMENT(.text.*))) and because the command
320 // line option is respected even if a SORT command is given, the exact
321 // behavior we have here is a bit complicated. Here are the rules.
323 // 1. If two SORT commands are given, --sort-section is ignored.
324 // 2. If one SORT command is given, and if it is not SORT_NONE,
325 // --sort-section is handled as an inner SORT command.
326 // 3. If one SORT command is given, and if it is SORT_NONE, don't sort.
327 // 4. If no SORT command is given, sort according to --sort-section.
328 InputSection **Begin = Ret.data() + SizeBefore;
329 InputSection **End = Ret.data() + Ret.size();
330 if (Pat.SortOuter != SortSectionPolicy::None) {
331 if (Pat.SortInner == SortSectionPolicy::Default)
332 sortSections(Begin, End, Config->SortSection);
334 sortSections(Begin, End, Pat.SortInner);
335 sortSections(Begin, End, Pat.SortOuter);
341 void LinkerScript::discard(ArrayRef<InputSectionBase *> V) {
342 for (InputSectionBase *S : V) {
344 if (S == InX::ShStrTab)
345 error("discarding .shstrtab section is not allowed");
346 discard(S->DependentSections);
350 std::vector<InputSectionBase *>
351 LinkerScript::createInputSectionList(OutputSectionCommand &OutCmd) {
352 std::vector<InputSectionBase *> Ret;
354 for (BaseCommand *Base : OutCmd.Commands) {
355 auto *Cmd = dyn_cast<InputSectionDescription>(Base);
359 Cmd->Sections = computeInputSections(Cmd);
360 Ret.insert(Ret.end(), Cmd->Sections.begin(), Cmd->Sections.end());
366 void LinkerScript::processCommands(OutputSectionFactory &Factory) {
367 // A symbol can be assigned before any section is mentioned in the linker
368 // script. In an DSO, the symbol values are addresses, so the only important
369 // section values are:
372 // * Any value meaning a regular section.
373 // To handle that, create a dummy aether section that fills the void before
374 // the linker scripts switches to another section. It has an index of one
375 // which will map to whatever the first actual section is.
376 Aether = make<OutputSection>("", 0, SHF_ALLOC);
377 Aether->SectionIndex = 1;
381 for (size_t I = 0; I < Opt.Commands.size(); ++I) {
382 // Handle symbol assignments outside of any output section.
383 if (auto *Cmd = dyn_cast<SymbolAssignment>(Opt.Commands[I])) {
388 if (auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I])) {
389 std::vector<InputSectionBase *> V = createInputSectionList(*Cmd);
391 // The output section name `/DISCARD/' is special.
392 // Any input section assigned to it is discarded.
393 if (Cmd->Name == "/DISCARD/") {
398 // This is for ONLY_IF_RO and ONLY_IF_RW. An output section directive
399 // ".foo : ONLY_IF_R[OW] { ... }" is handled only if all member input
400 // sections satisfy a given constraint. If not, a directive is handled
401 // as if it wasn't present from the beginning.
403 // Because we'll iterate over Commands many more times, the easiest
404 // way to "make it as if it wasn't present" is to just remove it.
405 if (!matchConstraints(V, Cmd->Constraint)) {
406 for (InputSectionBase *S : V)
408 Opt.Commands.erase(Opt.Commands.begin() + I);
413 // A directive may contain symbol definitions like this:
414 // ".foo : { ...; bar = .; }". Handle them.
415 for (BaseCommand *Base : Cmd->Commands)
416 if (auto *OutCmd = dyn_cast<SymbolAssignment>(Base))
419 // Handle subalign (e.g. ".foo : SUBALIGN(32) { ... }"). If subalign
420 // is given, input sections are aligned to that value, whether the
421 // given value is larger or smaller than the original section alignment.
422 if (Cmd->SubalignExpr) {
423 uint32_t Subalign = Cmd->SubalignExpr().getValue();
424 for (InputSectionBase *S : V)
425 S->Alignment = Subalign;
428 // Add input sections to an output section.
429 for (InputSectionBase *S : V)
430 Factory.addInputSec(S, Cmd->Name, Cmd->Sec);
431 if (OutputSection *Sec = Cmd->Sec) {
432 assert(Sec->SectionIndex == INT_MAX);
433 Sec->SectionIndex = I;
434 SecToCommand[Sec] = Cmd;
441 void LinkerScript::fabricateDefaultCommands() {
442 std::vector<BaseCommand *> Commands;
444 // Define start address
445 uint64_t StartAddr = Config->ImageBase + elf::getHeaderSize();
447 // The Sections with -T<section> have been sorted in order of ascending
448 // address. We must lower StartAddr if the lowest -T<section address> as
449 // calls to setDot() must be monotonically increasing.
450 for (auto& KV : Config->SectionStartMap)
451 StartAddr = std::min(StartAddr, KV.second);
454 make<SymbolAssignment>(".", [=] { return StartAddr; }, ""));
456 // For each OutputSection that needs a VA fabricate an OutputSectionCommand
457 // with an InputSectionDescription describing the InputSections
458 for (OutputSection *Sec : *OutputSections) {
459 auto *OSCmd = createOutputSectionCommand(Sec->Name, "<internal>");
461 SecToCommand[Sec] = OSCmd;
463 // Prefer user supplied address over additional alignment constraint
464 auto I = Config->SectionStartMap.find(Sec->Name);
465 if (I != Config->SectionStartMap.end())
467 make<SymbolAssignment>(".", [=] { return I->second; }, ""));
468 else if (Sec->PageAlign)
469 OSCmd->AddrExpr = [=] {
470 return alignTo(Script->getDot(), Config->MaxPageSize);
473 Commands.push_back(OSCmd);
474 if (Sec->Sections.size()) {
475 auto *ISD = make<InputSectionDescription>("");
476 OSCmd->Commands.push_back(ISD);
477 for (InputSection *ISec : Sec->Sections) {
478 ISD->Sections.push_back(ISec);
479 ISec->Assigned = true;
483 // SECTIONS commands run before other non SECTIONS commands
484 Commands.insert(Commands.end(), Opt.Commands.begin(), Opt.Commands.end());
485 Opt.Commands = std::move(Commands);
488 // Add sections that didn't match any sections command.
489 void LinkerScript::addOrphanSections(OutputSectionFactory &Factory) {
490 for (InputSectionBase *S : InputSections) {
491 if (!S->Live || S->Parent)
493 StringRef Name = getOutputSectionName(S->Name);
494 auto I = std::find_if(
495 Opt.Commands.begin(), Opt.Commands.end(), [&](BaseCommand *Base) {
496 if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base))
497 return Cmd->Name == Name;
500 if (I == Opt.Commands.end()) {
501 Factory.addInputSec(S, Name);
503 auto *Cmd = cast<OutputSectionCommand>(*I);
504 Factory.addInputSec(S, Name, Cmd->Sec);
505 if (OutputSection *Sec = Cmd->Sec) {
506 SecToCommand[Sec] = Cmd;
507 unsigned Index = std::distance(Opt.Commands.begin(), I);
508 assert(Sec->SectionIndex == INT_MAX || Sec->SectionIndex == Index);
509 Sec->SectionIndex = Index;
511 auto *ISD = make<InputSectionDescription>("");
512 ISD->Sections.push_back(cast<InputSection>(S));
513 Cmd->Commands.push_back(ISD);
518 uint64_t LinkerScript::advance(uint64_t Size, unsigned Align) {
519 bool IsTbss = (CurOutSec->Flags & SHF_TLS) && CurOutSec->Type == SHT_NOBITS;
520 uint64_t Start = IsTbss ? Dot + ThreadBssOffset : Dot;
521 Start = alignTo(Start, Align);
522 uint64_t End = Start + Size;
525 ThreadBssOffset = End - Dot;
531 void LinkerScript::output(InputSection *S) {
532 uint64_t Pos = advance(S->getSize(), S->Alignment);
533 S->OutSecOff = Pos - S->getSize() - CurOutSec->Addr;
535 // Update output section size after adding each section. This is so that
536 // SIZEOF works correctly in the case below:
537 // .foo { *(.aaa) a = SIZEOF(.foo); *(.bbb) }
538 CurOutSec->Size = Pos - CurOutSec->Addr;
540 // If there is a memory region associated with this input section, then
541 // place the section in that region and update the region index.
543 CurMemRegion->Offset += CurOutSec->Size;
544 uint64_t CurSize = CurMemRegion->Offset - CurMemRegion->Origin;
545 if (CurSize > CurMemRegion->Length) {
546 uint64_t OverflowAmt = CurSize - CurMemRegion->Length;
547 error("section '" + CurOutSec->Name + "' will not fit in region '" +
548 CurMemRegion->Name + "': overflowed by " + Twine(OverflowAmt) +
554 void LinkerScript::switchTo(OutputSection *Sec) {
555 if (CurOutSec == Sec)
559 CurOutSec->Addr = advance(0, CurOutSec->Alignment);
561 // If neither AT nor AT> is specified for an allocatable section, the linker
562 // will set the LMA such that the difference between VMA and LMA for the
563 // section is the same as the preceding output section in the same region
564 // https://sourceware.org/binutils/docs-2.20/ld/Output-Section-LMA.html
566 CurOutSec->LMAOffset = LMAOffset();
569 void LinkerScript::process(BaseCommand &Base) {
570 // This handles the assignments to symbol or to the dot.
571 if (auto *Cmd = dyn_cast<SymbolAssignment>(&Base)) {
572 assignSymbol(Cmd, true);
576 // Handle BYTE(), SHORT(), LONG(), or QUAD().
577 if (auto *Cmd = dyn_cast<BytesDataCommand>(&Base)) {
578 Cmd->Offset = Dot - CurOutSec->Addr;
580 CurOutSec->Size = Dot - CurOutSec->Addr;
585 if (auto *Cmd = dyn_cast<AssertCommand>(&Base)) {
590 // Handle a single input section description command.
591 // It calculates and assigns the offsets for each section and also
592 // updates the output section size.
593 auto &Cmd = cast<InputSectionDescription>(Base);
594 for (InputSection *Sec : Cmd.Sections) {
595 // We tentatively added all synthetic sections at the beginning and removed
596 // empty ones afterwards (because there is no way to know whether they were
597 // going be empty or not other than actually running linker scripts.)
598 // We need to ignore remains of empty sections.
599 if (auto *S = dyn_cast<SyntheticSection>(Sec))
605 assert(CurOutSec == Sec->getParent());
610 // This function searches for a memory region to place the given output
611 // section in. If found, a pointer to the appropriate memory region is
612 // returned. Otherwise, a nullptr is returned.
613 MemoryRegion *LinkerScript::findMemoryRegion(OutputSectionCommand *Cmd) {
614 // If a memory region name was specified in the output section command,
615 // then try to find that region first.
616 if (!Cmd->MemoryRegionName.empty()) {
617 auto It = Opt.MemoryRegions.find(Cmd->MemoryRegionName);
618 if (It != Opt.MemoryRegions.end())
620 error("memory region '" + Cmd->MemoryRegionName + "' not declared");
624 // If at least one memory region is defined, all sections must
625 // belong to some memory region. Otherwise, we don't need to do
626 // anything for memory regions.
627 if (Opt.MemoryRegions.empty())
630 OutputSection *Sec = Cmd->Sec;
631 // See if a region can be found by matching section flags.
632 for (auto &Pair : Opt.MemoryRegions) {
633 MemoryRegion &M = Pair.second;
634 if ((M.Flags & Sec->Flags) && (M.NegFlags & Sec->Flags) == 0)
638 // Otherwise, no suitable region was found.
639 if (Sec->Flags & SHF_ALLOC)
640 error("no memory region specified for section '" + Sec->Name + "'");
644 // This function assigns offsets to input sections and an output section
645 // for a single sections command (e.g. ".text { *(.text); }").
646 void LinkerScript::assignOffsets(OutputSectionCommand *Cmd) {
647 OutputSection *Sec = Cmd->Sec;
651 if (Cmd->AddrExpr && (Sec->Flags & SHF_ALLOC))
652 setDot(Cmd->AddrExpr, Cmd->Location, false);
656 LMAOffset = [=] { return Cmd->LMAExpr().getValue() - D; };
659 CurMemRegion = Cmd->MemRegion;
661 Dot = CurMemRegion->Offset;
664 // We do not support custom layout for compressed debug sectons.
665 // At this point we already know their size and have compressed content.
666 if (CurOutSec->Flags & SHF_COMPRESSED)
669 for (BaseCommand *C : Cmd->Commands)
673 void LinkerScript::removeEmptyCommands() {
674 // It is common practice to use very generic linker scripts. So for any
675 // given run some of the output sections in the script will be empty.
676 // We could create corresponding empty output sections, but that would
677 // clutter the output.
678 // We instead remove trivially empty sections. The bfd linker seems even
679 // more aggressive at removing them.
680 auto Pos = std::remove_if(
681 Opt.Commands.begin(), Opt.Commands.end(), [&](BaseCommand *Base) {
682 if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base))
683 return std::find(OutputSections->begin(), OutputSections->end(),
684 Cmd->Sec) == OutputSections->end();
687 Opt.Commands.erase(Pos, Opt.Commands.end());
690 static bool isAllSectionDescription(const OutputSectionCommand &Cmd) {
691 for (BaseCommand *Base : Cmd.Commands)
692 if (!isa<InputSectionDescription>(*Base))
697 void LinkerScript::adjustSectionsBeforeSorting() {
698 // If the output section contains only symbol assignments, create a
699 // corresponding output section. The bfd linker seems to only create them if
700 // '.' is assigned to, but creating these section should not have any bad
701 // consequeces and gives us a section to put the symbol in.
702 uint64_t Flags = SHF_ALLOC;
704 for (int I = 0, E = Opt.Commands.size(); I != E; ++I) {
705 auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I]);
708 if (OutputSection *Sec = Cmd->Sec) {
713 if (isAllSectionDescription(*Cmd))
716 auto *OutSec = make<OutputSection>(Cmd->Name, SHT_PROGBITS, Flags);
717 OutSec->SectionIndex = I;
718 OutputSections->push_back(OutSec);
720 SecToCommand[OutSec] = Cmd;
724 void LinkerScript::adjustSectionsAfterSorting() {
725 placeOrphanSections();
727 // Try and find an appropriate memory region to assign offsets in.
728 for (BaseCommand *Base : Opt.Commands) {
729 if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base)) {
730 Cmd->MemRegion = findMemoryRegion(Cmd);
731 // Handle align (e.g. ".foo : ALIGN(16) { ... }").
733 Cmd->Sec->updateAlignment(Cmd->AlignExpr().getValue());
737 // If output section command doesn't specify any segments,
738 // and we haven't previously assigned any section to segment,
739 // then we simply assign section to the very first load segment.
740 // Below is an example of such linker script:
741 // PHDRS { seg PT_LOAD; }
742 // SECTIONS { .aaa : { *(.aaa) } }
743 std::vector<StringRef> DefPhdrs;
745 std::find_if(Opt.PhdrsCommands.begin(), Opt.PhdrsCommands.end(),
746 [](const PhdrsCommand &Cmd) { return Cmd.Type == PT_LOAD; });
747 if (FirstPtLoad != Opt.PhdrsCommands.end())
748 DefPhdrs.push_back(FirstPtLoad->Name);
750 // Walk the commands and propagate the program headers to commands that don't
751 // explicitly specify them.
752 for (BaseCommand *Base : Opt.Commands) {
753 auto *Cmd = dyn_cast<OutputSectionCommand>(Base);
757 if (Cmd->Phdrs.empty())
758 Cmd->Phdrs = DefPhdrs;
760 DefPhdrs = Cmd->Phdrs;
763 removeEmptyCommands();
766 // When placing orphan sections, we want to place them after symbol assignments
767 // so that an orphan after
771 // doesn't break the intended meaning of the begin/end symbols.
772 // We don't want to go over sections since Writer<ELFT>::sortSections is the
773 // one in charge of deciding the order of the sections.
774 // We don't want to go over alignments, since doing so in
775 // rx_sec : { *(rx_sec) }
776 // . = ALIGN(0x1000);
777 // /* The RW PT_LOAD starts here*/
778 // rw_sec : { *(rw_sec) }
779 // would mean that the RW PT_LOAD would become unaligned.
780 static bool shouldSkip(BaseCommand *Cmd) {
781 if (isa<OutputSectionCommand>(Cmd))
783 if (auto *Assign = dyn_cast<SymbolAssignment>(Cmd))
784 return Assign->Name != ".";
788 // Orphan sections are sections present in the input files which are
789 // not explicitly placed into the output file by the linker script.
791 // When the control reaches this function, Opt.Commands contains
792 // output section commands for non-orphan sections only. This function
793 // adds new elements for orphan sections so that all sections are
794 // explicitly handled by Opt.Commands.
796 // Writer<ELFT>::sortSections has already sorted output sections.
797 // What we need to do is to scan OutputSections vector and
798 // Opt.Commands in parallel to find orphan sections. If there is an
799 // output section that doesn't have a corresponding entry in
800 // Opt.Commands, we will insert a new entry to Opt.Commands.
802 // There is some ambiguity as to where exactly a new entry should be
803 // inserted, because Opt.Commands contains not only output section
804 // commands but also other types of commands such as symbol assignment
805 // expressions. There's no correct answer here due to the lack of the
806 // formal specification of the linker script. We use heuristics to
807 // determine whether a new output command should be added before or
808 // after another commands. For the details, look at shouldSkip
810 void LinkerScript::placeOrphanSections() {
811 // The OutputSections are already in the correct order.
812 // This loops creates or moves commands as needed so that they are in the
816 // As a horrible special case, skip the first . assignment if it is before any
817 // section. We do this because it is common to set a load address by starting
818 // the script with ". = 0xabcd" and the expectation is that every section is
820 auto FirstSectionOrDotAssignment =
821 std::find_if(Opt.Commands.begin(), Opt.Commands.end(),
822 [](BaseCommand *Cmd) { return !shouldSkip(Cmd); });
823 if (FirstSectionOrDotAssignment != Opt.Commands.end()) {
824 CmdIndex = FirstSectionOrDotAssignment - Opt.Commands.begin();
825 if (isa<SymbolAssignment>(**FirstSectionOrDotAssignment))
829 for (OutputSection *Sec : *OutputSections) {
830 StringRef Name = Sec->Name;
832 // Find the last spot where we can insert a command and still get the
834 auto CmdIter = Opt.Commands.begin() + CmdIndex;
835 auto E = Opt.Commands.end();
836 while (CmdIter != E && shouldSkip(*CmdIter)) {
841 // If there is no command corresponding to this output section,
842 // create one and put a InputSectionDescription in it so that both
843 // representations agree on which input sections to use.
844 OutputSectionCommand *Cmd = getCmd(Sec);
846 Cmd = createOutputSectionCommand(Name, "<internal>");
847 Opt.Commands.insert(CmdIter, Cmd);
851 SecToCommand[Sec] = Cmd;
852 auto *ISD = make<InputSectionDescription>("");
853 for (InputSection *IS : Sec->Sections)
854 ISD->Sections.push_back(IS);
855 Cmd->Commands.push_back(ISD);
860 // Continue from where we found it.
861 while (*CmdIter != Cmd) {
869 void LinkerScript::processNonSectionCommands() {
870 for (BaseCommand *Base : Opt.Commands) {
871 if (auto *Cmd = dyn_cast<SymbolAssignment>(Base))
872 assignSymbol(Cmd, false);
873 else if (auto *Cmd = dyn_cast<AssertCommand>(Base))
878 // Do a last effort at synchronizing the linker script "AST" and the section
879 // list. This is needed to account for last minute changes, like adding a
880 // .ARM.exidx terminator and sorting SHF_LINK_ORDER sections.
882 // FIXME: We should instead create the "AST" earlier and the above changes would
883 // be done directly in the "AST".
885 // This can only handle new sections being added and sections being reordered.
886 void LinkerScript::synchronize() {
887 for (BaseCommand *Base : Opt.Commands) {
888 auto *Cmd = dyn_cast<OutputSectionCommand>(Base);
891 ArrayRef<InputSection *> Sections = Cmd->Sec->Sections;
892 std::vector<InputSection **> ScriptSections;
893 DenseSet<InputSection *> ScriptSectionsSet;
894 for (BaseCommand *Base : Cmd->Commands) {
895 auto *ISD = dyn_cast<InputSectionDescription>(Base);
898 for (InputSection *&IS : ISD->Sections) {
900 ScriptSections.push_back(&IS);
901 ScriptSectionsSet.insert(IS);
905 std::vector<InputSection *> Missing;
906 for (InputSection *IS : Sections)
907 if (!ScriptSectionsSet.count(IS))
908 Missing.push_back(IS);
909 if (!Missing.empty()) {
910 auto ISD = make<InputSectionDescription>("");
911 ISD->Sections = Missing;
912 Cmd->Commands.push_back(ISD);
913 for (InputSection *&IS : ISD->Sections)
915 ScriptSections.push_back(&IS);
917 assert(ScriptSections.size() == Sections.size());
918 for (int I = 0, N = Sections.size(); I < N; ++I)
919 *ScriptSections[I] = Sections[I];
924 allocateHeaders(std::vector<PhdrEntry> &Phdrs,
925 ArrayRef<OutputSectionCommand *> OutputSectionCommands,
928 std::find_if(Phdrs.begin(), Phdrs.end(),
929 [](const PhdrEntry &E) { return E.p_type == PT_LOAD; });
930 if (FirstPTLoad == Phdrs.end())
933 uint64_t HeaderSize = getHeaderSize();
934 if (HeaderSize <= Min || Script->hasPhdrsCommands()) {
935 Min = alignDown(Min - HeaderSize, Config->MaxPageSize);
936 Out::ElfHeader->Addr = Min;
937 Out::ProgramHeaders->Addr = Min + Out::ElfHeader->Size;
941 assert(FirstPTLoad->First == Out::ElfHeader);
942 OutputSection *ActualFirst = nullptr;
943 for (OutputSectionCommand *Cmd : OutputSectionCommands) {
944 OutputSection *Sec = Cmd->Sec;
945 if (Sec->FirstInPtLoad == Out::ElfHeader) {
951 for (OutputSectionCommand *Cmd : OutputSectionCommands) {
952 OutputSection *Sec = Cmd->Sec;
953 if (Sec->FirstInPtLoad == Out::ElfHeader)
954 Sec->FirstInPtLoad = ActualFirst;
956 FirstPTLoad->First = ActualFirst;
958 Phdrs.erase(FirstPTLoad);
961 auto PhdrI = std::find_if(Phdrs.begin(), Phdrs.end(), [](const PhdrEntry &E) {
962 return E.p_type == PT_PHDR;
964 if (PhdrI != Phdrs.end())
969 void LinkerScript::assignAddresses(
970 std::vector<PhdrEntry> &Phdrs,
971 ArrayRef<OutputSectionCommand *> OutputSectionCommands) {
972 // Assign addresses as instructed by linker script SECTIONS sub-commands.
974 ErrorOnMissingSection = true;
977 for (BaseCommand *Base : Opt.Commands) {
978 if (auto *Cmd = dyn_cast<SymbolAssignment>(Base)) {
979 assignSymbol(Cmd, false);
983 if (auto *Cmd = dyn_cast<AssertCommand>(Base)) {
988 auto *Cmd = cast<OutputSectionCommand>(Base);
992 uint64_t MinVA = std::numeric_limits<uint64_t>::max();
993 for (OutputSectionCommand *Cmd : OutputSectionCommands) {
994 OutputSection *Sec = Cmd->Sec;
995 if (Sec->Flags & SHF_ALLOC)
996 MinVA = std::min<uint64_t>(MinVA, Sec->Addr);
1001 allocateHeaders(Phdrs, OutputSectionCommands, MinVA);
1004 // Creates program headers as instructed by PHDRS linker script command.
1005 std::vector<PhdrEntry> LinkerScript::createPhdrs() {
1006 std::vector<PhdrEntry> Ret;
1008 // Process PHDRS and FILEHDR keywords because they are not
1009 // real output sections and cannot be added in the following loop.
1010 for (const PhdrsCommand &Cmd : Opt.PhdrsCommands) {
1011 Ret.emplace_back(Cmd.Type, Cmd.Flags == UINT_MAX ? PF_R : Cmd.Flags);
1012 PhdrEntry &Phdr = Ret.back();
1015 Phdr.add(Out::ElfHeader);
1017 Phdr.add(Out::ProgramHeaders);
1020 Phdr.p_paddr = Cmd.LMAExpr().getValue();
1025 // Add output sections to program headers.
1026 for (OutputSection *Sec : *OutputSections) {
1027 if (!(Sec->Flags & SHF_ALLOC))
1030 // Assign headers specified by linker script
1031 for (size_t Id : getPhdrIndices(Sec)) {
1033 if (Opt.PhdrsCommands[Id].Flags == UINT_MAX)
1034 Ret[Id].p_flags |= Sec->getPhdrFlags();
1040 bool LinkerScript::ignoreInterpSection() {
1041 // Ignore .interp section in case we have PHDRS specification
1042 // and PT_INTERP isn't listed.
1043 if (Opt.PhdrsCommands.empty())
1045 for (PhdrsCommand &Cmd : Opt.PhdrsCommands)
1046 if (Cmd.Type == PT_INTERP)
1051 OutputSectionCommand *LinkerScript::getCmd(OutputSection *Sec) const {
1052 auto I = SecToCommand.find(Sec);
1053 if (I == SecToCommand.end())
1058 uint32_t OutputSectionCommand::getFiller() {
1061 if (Sec->Flags & SHF_EXECINSTR)
1062 return Target->TrapInstr;
1066 static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
1070 write16(Buf, Data, Config->Endianness);
1072 write32(Buf, Data, Config->Endianness);
1074 write64(Buf, Data, Config->Endianness);
1076 llvm_unreachable("unsupported Size argument");
1079 // Compress section contents if this section contains debug info.
1080 template <class ELFT> void OutputSectionCommand::maybeCompress() {
1081 typedef typename ELFT::Chdr Elf_Chdr;
1083 // Compress only DWARF debug sections.
1084 if (!Config->CompressDebugSections || (Sec->Flags & SHF_ALLOC) ||
1085 !Name.startswith(".debug_"))
1088 // Create a section header.
1089 Sec->ZDebugHeader.resize(sizeof(Elf_Chdr));
1090 auto *Hdr = reinterpret_cast<Elf_Chdr *>(Sec->ZDebugHeader.data());
1091 Hdr->ch_type = ELFCOMPRESS_ZLIB;
1092 Hdr->ch_size = Sec->Size;
1093 Hdr->ch_addralign = Sec->Alignment;
1095 // Write section contents to a temporary buffer and compress it.
1096 std::vector<uint8_t> Buf(Sec->Size);
1097 writeTo<ELFT>(Buf.data());
1098 if (Error E = zlib::compress(toStringRef(Buf), Sec->CompressedData))
1099 fatal("compress failed: " + llvm::toString(std::move(E)));
1101 // Update section headers.
1102 Sec->Size = sizeof(Elf_Chdr) + Sec->CompressedData.size();
1103 Sec->Flags |= SHF_COMPRESSED;
1106 template <class ELFT> void OutputSectionCommand::writeTo(uint8_t *Buf) {
1109 // We may have already rendered compressed content when using
1110 // -compress-debug-sections option. Write it together with header.
1111 if (!Sec->CompressedData.empty()) {
1112 memcpy(Buf, Sec->ZDebugHeader.data(), Sec->ZDebugHeader.size());
1113 memcpy(Buf + Sec->ZDebugHeader.size(), Sec->CompressedData.data(),
1114 Sec->CompressedData.size());
1118 if (Sec->Type == SHT_NOBITS)
1121 // Write leading padding.
1122 std::vector<InputSection *> Sections;
1123 for (BaseCommand *Cmd : Commands)
1124 if (auto *ISD = dyn_cast<InputSectionDescription>(Cmd))
1125 for (InputSection *IS : ISD->Sections)
1127 Sections.push_back(IS);
1128 uint32_t Filler = getFiller();
1130 fill(Buf, Sections.empty() ? Sec->Size : Sections[0]->OutSecOff, Filler);
1132 parallelForEachN(0, Sections.size(), [=](size_t I) {
1133 InputSection *IS = Sections[I];
1134 IS->writeTo<ELFT>(Buf);
1136 // Fill gaps between sections.
1138 uint8_t *Start = Buf + IS->OutSecOff + IS->getSize();
1140 if (I + 1 == Sections.size())
1141 End = Buf + Sec->Size;
1143 End = Buf + Sections[I + 1]->OutSecOff;
1144 fill(Start, End - Start, Filler);
1148 // Linker scripts may have BYTE()-family commands with which you
1149 // can write arbitrary bytes to the output. Process them if any.
1150 for (BaseCommand *Base : Commands)
1151 if (auto *Data = dyn_cast<BytesDataCommand>(Base))
1152 writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
1155 bool LinkerScript::hasLMA(OutputSection *Sec) {
1156 if (OutputSectionCommand *Cmd = getCmd(Sec))
1162 ExprValue LinkerScript::getSymbolValue(const Twine &Loc, StringRef S) {
1164 return {CurOutSec, Dot - CurOutSec->Addr};
1165 if (SymbolBody *B = findSymbol(S)) {
1166 if (auto *D = dyn_cast<DefinedRegular>(B))
1167 return {D->Section, D->Value};
1168 if (auto *C = dyn_cast<DefinedCommon>(B))
1169 return {InX::Common, C->Offset};
1171 error(Loc + ": symbol not found: " + S);
1175 bool LinkerScript::isDefined(StringRef S) { return findSymbol(S) != nullptr; }
1177 // Returns indices of ELF headers containing specific section. Each index is a
1178 // zero based number of ELF header listed within PHDRS {} script block.
1179 std::vector<size_t> LinkerScript::getPhdrIndices(OutputSection *Sec) {
1180 if (OutputSectionCommand *Cmd = getCmd(Sec)) {
1181 std::vector<size_t> Ret;
1182 for (StringRef PhdrName : Cmd->Phdrs)
1183 Ret.push_back(getPhdrIndex(Cmd->Location, PhdrName));
1189 size_t LinkerScript::getPhdrIndex(const Twine &Loc, StringRef PhdrName) {
1191 for (PhdrsCommand &Cmd : Opt.PhdrsCommands) {
1192 if (Cmd.Name == PhdrName)
1196 error(Loc + ": section header '" + PhdrName + "' is not listed in PHDRS");
1200 template void OutputSectionCommand::writeTo<ELF32LE>(uint8_t *Buf);
1201 template void OutputSectionCommand::writeTo<ELF32BE>(uint8_t *Buf);
1202 template void OutputSectionCommand::writeTo<ELF64LE>(uint8_t *Buf);
1203 template void OutputSectionCommand::writeTo<ELF64BE>(uint8_t *Buf);
1205 template void OutputSectionCommand::maybeCompress<ELF32LE>();
1206 template void OutputSectionCommand::maybeCompress<ELF32BE>();
1207 template void OutputSectionCommand::maybeCompress<ELF64LE>();
1208 template void OutputSectionCommand::maybeCompress<ELF64BE>();