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"
24 #include "llvm/ADT/STLExtras.h"
25 #include "llvm/ADT/StringRef.h"
26 #include "llvm/Support/Casting.h"
27 #include "llvm/Support/ELF.h"
28 #include "llvm/Support/Endian.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/FileSystem.h"
31 #include "llvm/Support/Path.h"
42 using namespace llvm::ELF;
43 using namespace llvm::object;
44 using namespace llvm::support::endian;
46 using namespace lld::elf;
48 LinkerScript *elf::Script;
50 uint64_t ExprValue::getValue() const {
52 if (Sec->getOutputSection())
53 return Sec->getOffset(Val) + Sec->getOutputSection()->Addr;
54 error("unable to evaluate expression: input section " + Sec->Name +
55 " has no output section assigned");
60 uint64_t ExprValue::getSecAddr() const {
62 return Sec->getOffset(0) + Sec->getOutputSection()->Addr;
66 template <class ELFT> static SymbolBody *addRegular(SymbolAssignment *Cmd) {
68 uint8_t Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT;
69 std::tie(Sym, std::ignore) = Symtab<ELFT>::X->insert(
70 Cmd->Name, /*Type*/ 0, Visibility, /*CanOmitFromDynSym*/ false,
72 Sym->Binding = STB_GLOBAL;
73 ExprValue Value = Cmd->Expression();
74 SectionBase *Sec = Value.isAbsolute() ? nullptr : Value.Sec;
76 // We want to set symbol values early if we can. This allows us to use symbols
77 // as variables in linker scripts. Doing so allows us to write expressions
78 // like this: `alignment = 16; . = ALIGN(., alignment)`
79 uint64_t SymValue = Value.isAbsolute() ? Value.getValue() : 0;
80 replaceBody<DefinedRegular>(Sym, Cmd->Name, /*IsLocal=*/false, Visibility,
81 STT_NOTYPE, SymValue, 0, Sec, nullptr);
85 OutputSection *LinkerScript::getOutputSection(const Twine &Loc,
87 for (OutputSection *Sec : *OutputSections)
88 if (Sec->Name == Name)
91 static OutputSection Dummy("", 0, 0);
92 if (ErrorOnMissingSection)
93 error(Loc + ": undefined section " + Name);
97 // This function is essentially the same as getOutputSection(Name)->Size,
98 // but it won't print out an error message if a given section is not found.
100 // Linker script does not create an output section if its content is empty.
101 // We want to allow SIZEOF(.foo) where .foo is a section which happened to
102 // be empty. That is why this function is different from getOutputSection().
103 uint64_t LinkerScript::getOutputSectionSize(StringRef Name) {
104 for (OutputSection *Sec : *OutputSections)
105 if (Sec->Name == Name)
110 void LinkerScript::setDot(Expr E, const Twine &Loc, bool InSec) {
111 uint64_t Val = E().getValue();
114 error(Loc + ": unable to move location counter backward for: " +
117 error(Loc + ": unable to move location counter backward");
120 // Update to location counter means update to section size.
122 CurOutSec->Size = Dot - CurOutSec->Addr;
125 // Sets value of a symbol. Two kinds of symbols are processed: synthetic
126 // symbols, whose value is an offset from beginning of section and regular
127 // symbols whose value is absolute.
128 void LinkerScript::assignSymbol(SymbolAssignment *Cmd, bool InSec) {
129 if (Cmd->Name == ".") {
130 setDot(Cmd->Expression, Cmd->Location, InSec);
137 auto *Sym = cast<DefinedRegular>(Cmd->Sym);
138 ExprValue V = Cmd->Expression();
139 if (V.isAbsolute()) {
140 Sym->Value = V.getValue();
142 Sym->Section = V.Sec;
143 if (Sym->Section->Flags & SHF_ALLOC)
146 Sym->Value = V.getValue();
150 static SymbolBody *findSymbol(StringRef S) {
151 switch (Config->EKind) {
153 return Symtab<ELF32LE>::X->find(S);
155 return Symtab<ELF32BE>::X->find(S);
157 return Symtab<ELF64LE>::X->find(S);
159 return Symtab<ELF64BE>::X->find(S);
161 llvm_unreachable("unknown Config->EKind");
165 static SymbolBody *addRegularSymbol(SymbolAssignment *Cmd) {
166 switch (Config->EKind) {
168 return addRegular<ELF32LE>(Cmd);
170 return addRegular<ELF32BE>(Cmd);
172 return addRegular<ELF64LE>(Cmd);
174 return addRegular<ELF64BE>(Cmd);
176 llvm_unreachable("unknown Config->EKind");
180 void LinkerScript::addSymbol(SymbolAssignment *Cmd) {
181 if (Cmd->Name == ".")
184 // If a symbol was in PROVIDE(), we need to define it only when
185 // it is a referenced undefined symbol.
186 SymbolBody *B = findSymbol(Cmd->Name);
187 if (Cmd->Provide && (!B || B->isDefined()))
190 Cmd->Sym = addRegularSymbol(Cmd);
193 bool SymbolAssignment::classof(const BaseCommand *C) {
194 return C->Kind == AssignmentKind;
197 bool OutputSectionCommand::classof(const BaseCommand *C) {
198 return C->Kind == OutputSectionKind;
201 bool InputSectionDescription::classof(const BaseCommand *C) {
202 return C->Kind == InputSectionKind;
205 bool AssertCommand::classof(const BaseCommand *C) {
206 return C->Kind == AssertKind;
209 bool BytesDataCommand::classof(const BaseCommand *C) {
210 return C->Kind == BytesDataKind;
213 static StringRef basename(InputSectionBase *S) {
215 return sys::path::filename(S->File->getName());
219 bool LinkerScript::shouldKeep(InputSectionBase *S) {
220 for (InputSectionDescription *ID : Opt.KeptSections)
221 if (ID->FilePat.match(basename(S)))
222 for (SectionPattern &P : ID->SectionPatterns)
223 if (P.SectionPat.match(S->Name))
228 // A helper function for the SORT() command.
229 static std::function<bool(InputSectionBase *, InputSectionBase *)>
230 getComparator(SortSectionPolicy K) {
232 case SortSectionPolicy::Alignment:
233 return [](InputSectionBase *A, InputSectionBase *B) {
234 // ">" is not a mistake. Sections with larger alignments are placed
235 // before sections with smaller alignments in order to reduce the
236 // amount of padding necessary. This is compatible with GNU.
237 return A->Alignment > B->Alignment;
239 case SortSectionPolicy::Name:
240 return [](InputSectionBase *A, InputSectionBase *B) {
241 return A->Name < B->Name;
243 case SortSectionPolicy::Priority:
244 return [](InputSectionBase *A, InputSectionBase *B) {
245 return getPriority(A->Name) < getPriority(B->Name);
248 llvm_unreachable("unknown sort policy");
252 // A helper function for the SORT() command.
253 static bool matchConstraints(ArrayRef<InputSectionBase *> Sections,
254 ConstraintKind Kind) {
255 if (Kind == ConstraintKind::NoConstraint)
258 bool IsRW = llvm::any_of(Sections, [](InputSectionBase *Sec) {
259 return static_cast<InputSectionBase *>(Sec)->Flags & SHF_WRITE;
262 return (IsRW && Kind == ConstraintKind::ReadWrite) ||
263 (!IsRW && Kind == ConstraintKind::ReadOnly);
266 static void sortSections(InputSectionBase **Begin, InputSectionBase **End,
267 SortSectionPolicy K) {
268 if (K != SortSectionPolicy::Default && K != SortSectionPolicy::None)
269 std::stable_sort(Begin, End, getComparator(K));
272 // Compute and remember which sections the InputSectionDescription matches.
273 std::vector<InputSectionBase *>
274 LinkerScript::computeInputSections(const InputSectionDescription *Cmd) {
275 std::vector<InputSectionBase *> Ret;
277 // Collects all sections that satisfy constraints of Cmd.
278 for (const SectionPattern &Pat : Cmd->SectionPatterns) {
279 size_t SizeBefore = Ret.size();
281 for (InputSectionBase *Sec : InputSections) {
285 // For -emit-relocs we have to ignore entries like
286 // .rela.dyn : { *(.rela.data) }
287 // which are common because they are in the default bfd script.
288 if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
291 StringRef Filename = basename(Sec);
292 if (!Cmd->FilePat.match(Filename) ||
293 Pat.ExcludedFilePat.match(Filename) ||
294 !Pat.SectionPat.match(Sec->Name))
298 Sec->Assigned = true;
301 // Sort sections as instructed by SORT-family commands and --sort-section
302 // option. Because SORT-family commands can be nested at most two depth
303 // (e.g. SORT_BY_NAME(SORT_BY_ALIGNMENT(.text.*))) and because the command
304 // line option is respected even if a SORT command is given, the exact
305 // behavior we have here is a bit complicated. Here are the rules.
307 // 1. If two SORT commands are given, --sort-section is ignored.
308 // 2. If one SORT command is given, and if it is not SORT_NONE,
309 // --sort-section is handled as an inner SORT command.
310 // 3. If one SORT command is given, and if it is SORT_NONE, don't sort.
311 // 4. If no SORT command is given, sort according to --sort-section.
312 InputSectionBase **Begin = Ret.data() + SizeBefore;
313 InputSectionBase **End = Ret.data() + Ret.size();
314 if (Pat.SortOuter != SortSectionPolicy::None) {
315 if (Pat.SortInner == SortSectionPolicy::Default)
316 sortSections(Begin, End, Config->SortSection);
318 sortSections(Begin, End, Pat.SortInner);
319 sortSections(Begin, End, Pat.SortOuter);
325 void LinkerScript::discard(ArrayRef<InputSectionBase *> V) {
326 for (InputSectionBase *S : V) {
328 if (S == InX::ShStrTab)
329 error("discarding .shstrtab section is not allowed");
330 discard(S->DependentSections);
334 std::vector<InputSectionBase *>
335 LinkerScript::createInputSectionList(OutputSectionCommand &OutCmd) {
336 std::vector<InputSectionBase *> Ret;
338 for (BaseCommand *Base : OutCmd.Commands) {
339 auto *Cmd = dyn_cast<InputSectionDescription>(Base);
343 Cmd->Sections = computeInputSections(Cmd);
344 Ret.insert(Ret.end(), Cmd->Sections.begin(), Cmd->Sections.end());
350 void LinkerScript::processCommands(OutputSectionFactory &Factory) {
351 // A symbol can be assigned before any section is mentioned in the linker
352 // script. In an DSO, the symbol values are addresses, so the only important
353 // section values are:
356 // * Any value meaning a regular section.
357 // To handle that, create a dummy aether section that fills the void before
358 // the linker scripts switches to another section. It has an index of one
359 // which will map to whatever the first actual section is.
360 Aether = make<OutputSection>("", 0, SHF_ALLOC);
361 Aether->SectionIndex = 1;
365 for (size_t I = 0; I < Opt.Commands.size(); ++I) {
366 // Handle symbol assignments outside of any output section.
367 if (auto *Cmd = dyn_cast<SymbolAssignment>(Opt.Commands[I])) {
372 if (auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I])) {
373 std::vector<InputSectionBase *> V = createInputSectionList(*Cmd);
375 // The output section name `/DISCARD/' is special.
376 // Any input section assigned to it is discarded.
377 if (Cmd->Name == "/DISCARD/") {
382 // This is for ONLY_IF_RO and ONLY_IF_RW. An output section directive
383 // ".foo : ONLY_IF_R[OW] { ... }" is handled only if all member input
384 // sections satisfy a given constraint. If not, a directive is handled
385 // as if it wasn't present from the beginning.
387 // Because we'll iterate over Commands many more times, the easiest
388 // way to "make it as if it wasn't present" is to just remove it.
389 if (!matchConstraints(V, Cmd->Constraint)) {
390 for (InputSectionBase *S : V)
392 Opt.Commands.erase(Opt.Commands.begin() + I);
397 // A directive may contain symbol definitions like this:
398 // ".foo : { ...; bar = .; }". Handle them.
399 for (BaseCommand *Base : Cmd->Commands)
400 if (auto *OutCmd = dyn_cast<SymbolAssignment>(Base))
403 // Handle subalign (e.g. ".foo : SUBALIGN(32) { ... }"). If subalign
404 // is given, input sections are aligned to that value, whether the
405 // given value is larger or smaller than the original section alignment.
406 if (Cmd->SubalignExpr) {
407 uint32_t Subalign = Cmd->SubalignExpr().getValue();
408 for (InputSectionBase *S : V)
409 S->Alignment = Subalign;
412 // Add input sections to an output section.
413 for (InputSectionBase *S : V)
414 Factory.addInputSec(S, Cmd->Name, Cmd->Sec);
415 if (OutputSection *Sec = Cmd->Sec) {
416 assert(Sec->SectionIndex == INT_MAX);
417 Sec->SectionIndex = I;
418 SecToCommand[Sec] = Cmd;
425 void LinkerScript::fabricateDefaultCommands() {
426 std::vector<BaseCommand *> Commands;
428 // Define start address
429 uint64_t StartAddr = Config->ImageBase + elf::getHeaderSize();
431 // The Sections with -T<section> have been sorted in order of ascending
432 // address. We must lower StartAddr if the lowest -T<section address> as
433 // calls to setDot() must be monotonically increasing.
434 for (auto& KV : Config->SectionStartMap)
435 StartAddr = std::min(StartAddr, KV.second);
438 make<SymbolAssignment>(".", [=] { return StartAddr; }, ""));
440 // For each OutputSection that needs a VA fabricate an OutputSectionCommand
441 // with an InputSectionDescription describing the InputSections
442 for (OutputSection *Sec : *OutputSections) {
443 auto *OSCmd = make<OutputSectionCommand>(Sec->Name);
445 SecToCommand[Sec] = OSCmd;
447 // Prefer user supplied address over additional alignment constraint
448 auto I = Config->SectionStartMap.find(Sec->Name);
449 if (I != Config->SectionStartMap.end())
451 make<SymbolAssignment>(".", [=] { return I->second; }, ""));
452 else if (Sec->PageAlign)
453 OSCmd->AddrExpr = [=] {
454 return alignTo(Script->getDot(), Config->MaxPageSize);
457 Commands.push_back(OSCmd);
458 if (Sec->Sections.size()) {
459 auto *ISD = make<InputSectionDescription>("");
460 OSCmd->Commands.push_back(ISD);
461 for (InputSection *ISec : Sec->Sections) {
462 ISD->Sections.push_back(ISec);
463 ISec->Assigned = true;
467 // SECTIONS commands run before other non SECTIONS commands
468 Commands.insert(Commands.end(), Opt.Commands.begin(), Opt.Commands.end());
469 Opt.Commands = std::move(Commands);
472 // Add sections that didn't match any sections command.
473 void LinkerScript::addOrphanSections(OutputSectionFactory &Factory) {
474 for (InputSectionBase *S : InputSections) {
475 if (!S->Live || S->OutSec)
477 StringRef Name = getOutputSectionName(S->Name);
478 auto I = std::find_if(
479 Opt.Commands.begin(), Opt.Commands.end(), [&](BaseCommand *Base) {
480 if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base))
481 return Cmd->Name == Name;
484 if (I == Opt.Commands.end()) {
485 Factory.addInputSec(S, Name);
487 auto *Cmd = cast<OutputSectionCommand>(*I);
488 Factory.addInputSec(S, Name, Cmd->Sec);
489 if (OutputSection *Sec = Cmd->Sec) {
490 SecToCommand[Sec] = Cmd;
491 unsigned Index = std::distance(Opt.Commands.begin(), I);
492 assert(Sec->SectionIndex == INT_MAX || Sec->SectionIndex == Index);
493 Sec->SectionIndex = Index;
495 auto *ISD = make<InputSectionDescription>("");
496 ISD->Sections.push_back(S);
497 Cmd->Commands.push_back(ISD);
502 uint64_t LinkerScript::advance(uint64_t Size, unsigned Align) {
503 bool IsTbss = (CurOutSec->Flags & SHF_TLS) && CurOutSec->Type == SHT_NOBITS;
504 uint64_t Start = IsTbss ? Dot + ThreadBssOffset : Dot;
505 Start = alignTo(Start, Align);
506 uint64_t End = Start + Size;
509 ThreadBssOffset = End - Dot;
515 void LinkerScript::output(InputSection *S) {
516 uint64_t Pos = advance(S->getSize(), S->Alignment);
517 S->OutSecOff = Pos - S->getSize() - CurOutSec->Addr;
519 // Update output section size after adding each section. This is so that
520 // SIZEOF works correctly in the case below:
521 // .foo { *(.aaa) a = SIZEOF(.foo); *(.bbb) }
522 CurOutSec->Size = Pos - CurOutSec->Addr;
524 // If there is a memory region associated with this input section, then
525 // place the section in that region and update the region index.
527 CurMemRegion->Offset += CurOutSec->Size;
528 uint64_t CurSize = CurMemRegion->Offset - CurMemRegion->Origin;
529 if (CurSize > CurMemRegion->Length) {
530 uint64_t OverflowAmt = CurSize - CurMemRegion->Length;
531 error("section '" + CurOutSec->Name + "' will not fit in region '" +
532 CurMemRegion->Name + "': overflowed by " + Twine(OverflowAmt) +
538 void LinkerScript::switchTo(OutputSection *Sec) {
539 if (CurOutSec == Sec)
543 CurOutSec->Addr = advance(0, CurOutSec->Alignment);
545 // If neither AT nor AT> is specified for an allocatable section, the linker
546 // will set the LMA such that the difference between VMA and LMA for the
547 // section is the same as the preceding output section in the same region
548 // https://sourceware.org/binutils/docs-2.20/ld/Output-Section-LMA.html
550 CurOutSec->LMAOffset = LMAOffset();
553 void LinkerScript::process(BaseCommand &Base) {
554 // This handles the assignments to symbol or to the dot.
555 if (auto *Cmd = dyn_cast<SymbolAssignment>(&Base)) {
556 assignSymbol(Cmd, true);
560 // Handle BYTE(), SHORT(), LONG(), or QUAD().
561 if (auto *Cmd = dyn_cast<BytesDataCommand>(&Base)) {
562 Cmd->Offset = Dot - CurOutSec->Addr;
564 CurOutSec->Size = Dot - CurOutSec->Addr;
569 if (auto *Cmd = dyn_cast<AssertCommand>(&Base)) {
574 // Handle a single input section description command.
575 // It calculates and assigns the offsets for each section and also
576 // updates the output section size.
577 auto &Cmd = cast<InputSectionDescription>(Base);
578 for (InputSectionBase *Sec : Cmd.Sections) {
579 // We tentatively added all synthetic sections at the beginning and removed
580 // empty ones afterwards (because there is no way to know whether they were
581 // going be empty or not other than actually running linker scripts.)
582 // We need to ignore remains of empty sections.
583 if (auto *S = dyn_cast<SyntheticSection>(Sec))
589 assert(CurOutSec == Sec->OutSec);
590 output(cast<InputSection>(Sec));
594 // This function searches for a memory region to place the given output
595 // section in. If found, a pointer to the appropriate memory region is
596 // returned. Otherwise, a nullptr is returned.
597 MemoryRegion *LinkerScript::findMemoryRegion(OutputSectionCommand *Cmd) {
598 // If a memory region name was specified in the output section command,
599 // then try to find that region first.
600 if (!Cmd->MemoryRegionName.empty()) {
601 auto It = Opt.MemoryRegions.find(Cmd->MemoryRegionName);
602 if (It != Opt.MemoryRegions.end())
604 error("memory region '" + Cmd->MemoryRegionName + "' not declared");
608 // If at least one memory region is defined, all sections must
609 // belong to some memory region. Otherwise, we don't need to do
610 // anything for memory regions.
611 if (Opt.MemoryRegions.empty())
614 OutputSection *Sec = Cmd->Sec;
615 // See if a region can be found by matching section flags.
616 for (auto &Pair : Opt.MemoryRegions) {
617 MemoryRegion &M = Pair.second;
618 if ((M.Flags & Sec->Flags) && (M.NegFlags & Sec->Flags) == 0)
622 // Otherwise, no suitable region was found.
623 if (Sec->Flags & SHF_ALLOC)
624 error("no memory region specified for section '" + Sec->Name + "'");
628 // This function assigns offsets to input sections and an output section
629 // for a single sections command (e.g. ".text { *(.text); }").
630 void LinkerScript::assignOffsets(OutputSectionCommand *Cmd) {
631 OutputSection *Sec = Cmd->Sec;
635 if (Cmd->AddrExpr && (Sec->Flags & SHF_ALLOC))
636 setDot(Cmd->AddrExpr, Cmd->Location, false);
640 LMAOffset = [=] { return Cmd->LMAExpr().getValue() - D; };
643 CurMemRegion = Cmd->MemRegion;
645 Dot = CurMemRegion->Offset;
648 // We do not support custom layout for compressed debug sectons.
649 // At this point we already know their size and have compressed content.
650 if (CurOutSec->Flags & SHF_COMPRESSED)
653 for (BaseCommand *C : Cmd->Commands)
657 void LinkerScript::removeEmptyCommands() {
658 // It is common practice to use very generic linker scripts. So for any
659 // given run some of the output sections in the script will be empty.
660 // We could create corresponding empty output sections, but that would
661 // clutter the output.
662 // We instead remove trivially empty sections. The bfd linker seems even
663 // more aggressive at removing them.
664 auto Pos = std::remove_if(
665 Opt.Commands.begin(), Opt.Commands.end(), [&](BaseCommand *Base) {
666 if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base))
667 return std::find(OutputSections->begin(), OutputSections->end(),
668 Cmd->Sec) == OutputSections->end();
671 Opt.Commands.erase(Pos, Opt.Commands.end());
674 static bool isAllSectionDescription(const OutputSectionCommand &Cmd) {
675 for (BaseCommand *Base : Cmd.Commands)
676 if (!isa<InputSectionDescription>(*Base))
681 void LinkerScript::adjustSectionsBeforeSorting() {
682 // If the output section contains only symbol assignments, create a
683 // corresponding output section. The bfd linker seems to only create them if
684 // '.' is assigned to, but creating these section should not have any bad
685 // consequeces and gives us a section to put the symbol in.
686 uint64_t Flags = SHF_ALLOC;
687 uint32_t Type = SHT_PROGBITS;
689 for (int I = 0, E = Opt.Commands.size(); I != E; ++I) {
690 auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I]);
693 if (OutputSection *Sec = Cmd->Sec) {
699 if (isAllSectionDescription(*Cmd))
702 auto *OutSec = make<OutputSection>(Cmd->Name, Type, Flags);
703 OutSec->SectionIndex = I;
704 OutputSections->push_back(OutSec);
706 SecToCommand[OutSec] = Cmd;
710 void LinkerScript::adjustSectionsAfterSorting() {
711 placeOrphanSections();
713 // Try and find an appropriate memory region to assign offsets in.
714 for (BaseCommand *Base : Opt.Commands) {
715 if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base)) {
716 Cmd->MemRegion = findMemoryRegion(Cmd);
717 // Handle align (e.g. ".foo : ALIGN(16) { ... }").
719 Cmd->Sec->updateAlignment(Cmd->AlignExpr().getValue());
723 // If output section command doesn't specify any segments,
724 // and we haven't previously assigned any section to segment,
725 // then we simply assign section to the very first load segment.
726 // Below is an example of such linker script:
727 // PHDRS { seg PT_LOAD; }
728 // SECTIONS { .aaa : { *(.aaa) } }
729 std::vector<StringRef> DefPhdrs;
731 std::find_if(Opt.PhdrsCommands.begin(), Opt.PhdrsCommands.end(),
732 [](const PhdrsCommand &Cmd) { return Cmd.Type == PT_LOAD; });
733 if (FirstPtLoad != Opt.PhdrsCommands.end())
734 DefPhdrs.push_back(FirstPtLoad->Name);
736 // Walk the commands and propagate the program headers to commands that don't
737 // explicitly specify them.
738 for (BaseCommand *Base : Opt.Commands) {
739 auto *Cmd = dyn_cast<OutputSectionCommand>(Base);
743 if (Cmd->Phdrs.empty())
744 Cmd->Phdrs = DefPhdrs;
746 DefPhdrs = Cmd->Phdrs;
749 removeEmptyCommands();
752 // When placing orphan sections, we want to place them after symbol assignments
753 // so that an orphan after
757 // doesn't break the intended meaning of the begin/end symbols.
758 // We don't want to go over sections since Writer<ELFT>::sortSections is the
759 // one in charge of deciding the order of the sections.
760 // We don't want to go over alignments, since doing so in
761 // rx_sec : { *(rx_sec) }
762 // . = ALIGN(0x1000);
763 // /* The RW PT_LOAD starts here*/
764 // rw_sec : { *(rw_sec) }
765 // would mean that the RW PT_LOAD would become unaligned.
766 static bool shouldSkip(BaseCommand *Cmd) {
767 if (isa<OutputSectionCommand>(Cmd))
769 if (auto *Assign = dyn_cast<SymbolAssignment>(Cmd))
770 return Assign->Name != ".";
774 // Orphan sections are sections present in the input files which are
775 // not explicitly placed into the output file by the linker script.
777 // When the control reaches this function, Opt.Commands contains
778 // output section commands for non-orphan sections only. This function
779 // adds new elements for orphan sections so that all sections are
780 // explicitly handled by Opt.Commands.
782 // Writer<ELFT>::sortSections has already sorted output sections.
783 // What we need to do is to scan OutputSections vector and
784 // Opt.Commands in parallel to find orphan sections. If there is an
785 // output section that doesn't have a corresponding entry in
786 // Opt.Commands, we will insert a new entry to Opt.Commands.
788 // There is some ambiguity as to where exactly a new entry should be
789 // inserted, because Opt.Commands contains not only output section
790 // commands but also other types of commands such as symbol assignment
791 // expressions. There's no correct answer here due to the lack of the
792 // formal specification of the linker script. We use heuristics to
793 // determine whether a new output command should be added before or
794 // after another commands. For the details, look at shouldSkip
796 void LinkerScript::placeOrphanSections() {
797 // The OutputSections are already in the correct order.
798 // This loops creates or moves commands as needed so that they are in the
802 // As a horrible special case, skip the first . assignment if it is before any
803 // section. We do this because it is common to set a load address by starting
804 // the script with ". = 0xabcd" and the expectation is that every section is
806 auto FirstSectionOrDotAssignment =
807 std::find_if(Opt.Commands.begin(), Opt.Commands.end(),
808 [](BaseCommand *Cmd) { return !shouldSkip(Cmd); });
809 if (FirstSectionOrDotAssignment != Opt.Commands.end()) {
810 CmdIndex = FirstSectionOrDotAssignment - Opt.Commands.begin();
811 if (isa<SymbolAssignment>(**FirstSectionOrDotAssignment))
815 for (OutputSection *Sec : *OutputSections) {
816 StringRef Name = Sec->Name;
818 // Find the last spot where we can insert a command and still get the
820 auto CmdIter = Opt.Commands.begin() + CmdIndex;
821 auto E = Opt.Commands.end();
822 while (CmdIter != E && shouldSkip(*CmdIter)) {
827 // If there is no command corresponding to this output section,
828 // create one and put a InputSectionDescription in it so that both
829 // representations agree on which input sections to use.
830 OutputSectionCommand *Cmd = getCmd(Sec);
832 Cmd = make<OutputSectionCommand>(Name);
833 Opt.Commands.insert(CmdIter, Cmd);
837 SecToCommand[Sec] = Cmd;
838 auto *ISD = make<InputSectionDescription>("");
839 for (InputSection *IS : Sec->Sections)
840 ISD->Sections.push_back(IS);
841 Cmd->Commands.push_back(ISD);
846 // Continue from where we found it.
847 while (*CmdIter != Cmd) {
855 void LinkerScript::processNonSectionCommands() {
856 for (BaseCommand *Base : Opt.Commands) {
857 if (auto *Cmd = dyn_cast<SymbolAssignment>(Base))
858 assignSymbol(Cmd, false);
859 else if (auto *Cmd = dyn_cast<AssertCommand>(Base))
864 // Do a last effort at synchronizing the linker script "AST" and the section
865 // list. This is needed to account for last minute changes, like adding a
866 // .ARM.exidx terminator and sorting SHF_LINK_ORDER sections.
868 // FIXME: We should instead create the "AST" earlier and the above changes would
869 // be done directly in the "AST".
871 // This can only handle new sections being added and sections being reordered.
872 void LinkerScript::synchronize() {
873 for (BaseCommand *Base : Opt.Commands) {
874 auto *Cmd = dyn_cast<OutputSectionCommand>(Base);
877 ArrayRef<InputSection *> Sections = Cmd->Sec->Sections;
878 std::vector<InputSectionBase **> ScriptSections;
879 DenseSet<InputSectionBase *> ScriptSectionsSet;
880 for (BaseCommand *Base : Cmd->Commands) {
881 auto *ISD = dyn_cast<InputSectionDescription>(Base);
884 for (InputSectionBase *&IS : ISD->Sections) {
886 ScriptSections.push_back(&IS);
887 ScriptSectionsSet.insert(IS);
891 std::vector<InputSectionBase *> Missing;
892 for (InputSection *IS : Sections)
893 if (!ScriptSectionsSet.count(IS))
894 Missing.push_back(IS);
895 if (!Missing.empty()) {
896 auto ISD = make<InputSectionDescription>("");
897 ISD->Sections = Missing;
898 Cmd->Commands.push_back(ISD);
899 for (InputSectionBase *&IS : ISD->Sections)
901 ScriptSections.push_back(&IS);
903 assert(ScriptSections.size() == Sections.size());
904 for (int I = 0, N = Sections.size(); I < N; ++I)
905 *ScriptSections[I] = Sections[I];
909 static bool allocateHeaders(std::vector<PhdrEntry> &Phdrs,
910 ArrayRef<OutputSection *> OutputSections,
913 std::find_if(Phdrs.begin(), Phdrs.end(),
914 [](const PhdrEntry &E) { return E.p_type == PT_LOAD; });
915 if (FirstPTLoad == Phdrs.end())
918 uint64_t HeaderSize = getHeaderSize();
919 if (HeaderSize <= Min || Script->hasPhdrsCommands()) {
920 Min = alignDown(Min - HeaderSize, Config->MaxPageSize);
921 Out::ElfHeader->Addr = Min;
922 Out::ProgramHeaders->Addr = Min + Out::ElfHeader->Size;
926 assert(FirstPTLoad->First == Out::ElfHeader);
927 OutputSection *ActualFirst = nullptr;
928 for (OutputSection *Sec : OutputSections) {
929 if (Sec->FirstInPtLoad == Out::ElfHeader) {
935 for (OutputSection *Sec : OutputSections)
936 if (Sec->FirstInPtLoad == Out::ElfHeader)
937 Sec->FirstInPtLoad = ActualFirst;
938 FirstPTLoad->First = ActualFirst;
940 Phdrs.erase(FirstPTLoad);
943 auto PhdrI = std::find_if(Phdrs.begin(), Phdrs.end(), [](const PhdrEntry &E) {
944 return E.p_type == PT_PHDR;
946 if (PhdrI != Phdrs.end())
951 void LinkerScript::assignAddresses(std::vector<PhdrEntry> &Phdrs) {
952 // Assign addresses as instructed by linker script SECTIONS sub-commands.
954 ErrorOnMissingSection = true;
957 for (BaseCommand *Base : Opt.Commands) {
958 if (auto *Cmd = dyn_cast<SymbolAssignment>(Base)) {
959 assignSymbol(Cmd, false);
963 if (auto *Cmd = dyn_cast<AssertCommand>(Base)) {
968 auto *Cmd = cast<OutputSectionCommand>(Base);
972 uint64_t MinVA = std::numeric_limits<uint64_t>::max();
973 for (OutputSection *Sec : *OutputSections) {
974 if (Sec->Flags & SHF_ALLOC)
975 MinVA = std::min<uint64_t>(MinVA, Sec->Addr);
980 allocateHeaders(Phdrs, *OutputSections, MinVA);
983 // Creates program headers as instructed by PHDRS linker script command.
984 std::vector<PhdrEntry> LinkerScript::createPhdrs() {
985 std::vector<PhdrEntry> Ret;
987 // Process PHDRS and FILEHDR keywords because they are not
988 // real output sections and cannot be added in the following loop.
989 for (const PhdrsCommand &Cmd : Opt.PhdrsCommands) {
990 Ret.emplace_back(Cmd.Type, Cmd.Flags == UINT_MAX ? PF_R : Cmd.Flags);
991 PhdrEntry &Phdr = Ret.back();
994 Phdr.add(Out::ElfHeader);
996 Phdr.add(Out::ProgramHeaders);
999 Phdr.p_paddr = Cmd.LMAExpr().getValue();
1004 // Add output sections to program headers.
1005 for (OutputSection *Sec : *OutputSections) {
1006 if (!(Sec->Flags & SHF_ALLOC))
1009 // Assign headers specified by linker script
1010 for (size_t Id : getPhdrIndices(Sec)) {
1012 if (Opt.PhdrsCommands[Id].Flags == UINT_MAX)
1013 Ret[Id].p_flags |= Sec->getPhdrFlags();
1019 bool LinkerScript::ignoreInterpSection() {
1020 // Ignore .interp section in case we have PHDRS specification
1021 // and PT_INTERP isn't listed.
1022 if (Opt.PhdrsCommands.empty())
1024 for (PhdrsCommand &Cmd : Opt.PhdrsCommands)
1025 if (Cmd.Type == PT_INTERP)
1030 OutputSectionCommand *LinkerScript::getCmd(OutputSection *Sec) const {
1031 auto I = SecToCommand.find(Sec);
1032 if (I == SecToCommand.end())
1037 Optional<uint32_t> LinkerScript::getFiller(OutputSection *Sec) {
1038 if (OutputSectionCommand *Cmd = getCmd(Sec))
1043 static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
1047 write16(Buf, Data, Config->Endianness);
1049 write32(Buf, Data, Config->Endianness);
1051 write64(Buf, Data, Config->Endianness);
1053 llvm_unreachable("unsupported Size argument");
1056 void LinkerScript::writeDataBytes(OutputSection *Sec, uint8_t *Buf) {
1057 if (OutputSectionCommand *Cmd = getCmd(Sec))
1058 for (BaseCommand *Base : Cmd->Commands)
1059 if (auto *Data = dyn_cast<BytesDataCommand>(Base))
1060 writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
1063 bool LinkerScript::hasLMA(OutputSection *Sec) {
1064 if (OutputSectionCommand *Cmd = getCmd(Sec))
1070 ExprValue LinkerScript::getSymbolValue(const Twine &Loc, StringRef S) {
1072 return {CurOutSec, Dot - CurOutSec->Addr};
1073 if (SymbolBody *B = findSymbol(S)) {
1074 if (auto *D = dyn_cast<DefinedRegular>(B))
1075 return {D->Section, D->Value};
1076 if (auto *C = dyn_cast<DefinedCommon>(B))
1077 return {InX::Common, C->Offset};
1079 error(Loc + ": symbol not found: " + S);
1083 bool LinkerScript::isDefined(StringRef S) { return findSymbol(S) != nullptr; }
1085 // Returns indices of ELF headers containing specific section. Each index is a
1086 // zero based number of ELF header listed within PHDRS {} script block.
1087 std::vector<size_t> LinkerScript::getPhdrIndices(OutputSection *Sec) {
1088 if (OutputSectionCommand *Cmd = getCmd(Sec)) {
1089 std::vector<size_t> Ret;
1090 for (StringRef PhdrName : Cmd->Phdrs)
1091 Ret.push_back(getPhdrIndex(Cmd->Location, PhdrName));
1097 size_t LinkerScript::getPhdrIndex(const Twine &Loc, StringRef PhdrName) {
1099 for (PhdrsCommand &Cmd : Opt.PhdrsCommands) {
1100 if (Cmd.Name == PhdrName)
1104 error(Loc + ": section header '" + PhdrName + "' is not listed in PHDRS");