diff options
Diffstat (limited to 'ELF/LinkerScript.cpp')
| -rw-r--r-- | ELF/LinkerScript.cpp | 1381 |
1 files changed, 573 insertions, 808 deletions
diff --git a/ELF/LinkerScript.cpp b/ELF/LinkerScript.cpp index 8bdbd8db20add..91873e318f545 100644 --- a/ELF/LinkerScript.cpp +++ b/ELF/LinkerScript.cpp @@ -14,20 +14,19 @@ #include "LinkerScript.h" #include "Config.h" #include "InputSection.h" -#include "Memory.h" #include "OutputSections.h" #include "Strings.h" #include "SymbolTable.h" #include "Symbols.h" #include "SyntheticSections.h" #include "Target.h" -#include "Threads.h" #include "Writer.h" +#include "lld/Common/Memory.h" +#include "lld/Common/Threads.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/StringRef.h" #include "llvm/BinaryFormat/ELF.h" #include "llvm/Support/Casting.h" -#include "llvm/Support/Compression.h" #include "llvm/Support/Endian.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/FileSystem.h" @@ -50,62 +49,56 @@ using namespace lld::elf; LinkerScript *elf::Script; +static uint64_t getOutputSectionVA(SectionBase *InputSec, StringRef Loc) { + if (OutputSection *OS = InputSec->getOutputSection()) + return OS->Addr; + error(Loc + ": unable to evaluate expression: input section " + + InputSec->Name + " has no output section assigned"); + return 0; +} + uint64_t ExprValue::getValue() const { - if (Sec) { - if (OutputSection *OS = Sec->getOutputSection()) - return alignTo(Sec->getOffset(Val) + OS->Addr, Alignment); - error(Loc + ": unable to evaluate expression: input section " + Sec->Name + - " has no output section assigned"); - } + if (Sec) + return alignTo(Sec->getOffset(Val) + getOutputSectionVA(Sec, Loc), + Alignment); return alignTo(Val, Alignment); } uint64_t ExprValue::getSecAddr() const { if (Sec) - return Sec->getOffset(0) + Sec->getOutputSection()->Addr; + return Sec->getOffset(0) + getOutputSectionVA(Sec, Loc); return 0; } -template <class ELFT> static SymbolBody *addRegular(SymbolAssignment *Cmd) { - Symbol *Sym; - uint8_t Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT; - std::tie(Sym, std::ignore) = Symtab<ELFT>::X->insert( - Cmd->Name, /*Type*/ 0, Visibility, /*CanOmitFromDynSym*/ false, - /*File*/ nullptr); - Sym->Binding = STB_GLOBAL; - ExprValue Value = Cmd->Expression(); - SectionBase *Sec = Value.isAbsolute() ? nullptr : Value.Sec; - - // We want to set symbol values early if we can. This allows us to use symbols - // as variables in linker scripts. Doing so allows us to write expressions - // like this: `alignment = 16; . = ALIGN(., alignment)` - uint64_t SymValue = Value.isAbsolute() ? Value.getValue() : 0; - replaceBody<DefinedRegular>(Sym, Cmd->Name, /*IsLocal=*/false, Visibility, - STT_NOTYPE, SymValue, 0, Sec, nullptr); - return Sym->body(); +uint64_t ExprValue::getSectionOffset() const { + // If the alignment is trivial, we don't have to compute the full + // value to know the offset. This allows this function to succeed in + // cases where the output section is not yet known. + if (Alignment == 1) + return Val; + return getValue() - getSecAddr(); } -OutputSectionCommand * -LinkerScript::createOutputSectionCommand(StringRef Name, StringRef Location) { - OutputSectionCommand *&CmdRef = NameToOutputSectionCommand[Name]; - OutputSectionCommand *Cmd; - if (CmdRef && CmdRef->Location.empty()) { +OutputSection *LinkerScript::createOutputSection(StringRef Name, + StringRef Location) { + OutputSection *&SecRef = NameToOutputSection[Name]; + OutputSection *Sec; + if (SecRef && SecRef->Location.empty()) { // There was a forward reference. - Cmd = CmdRef; + Sec = SecRef; } else { - Cmd = make<OutputSectionCommand>(Name); - if (!CmdRef) - CmdRef = Cmd; + Sec = make<OutputSection>(Name, SHT_NOBITS, 0); + if (!SecRef) + SecRef = Sec; } - Cmd->Location = Location; - return Cmd; + Sec->Location = Location; + return Sec; } -OutputSectionCommand * -LinkerScript::getOrCreateOutputSectionCommand(StringRef Name) { - OutputSectionCommand *&CmdRef = NameToOutputSectionCommand[Name]; +OutputSection *LinkerScript::getOrCreateOutputSection(StringRef Name) { + OutputSection *&CmdRef = NameToOutputSection[Name]; if (!CmdRef) - CmdRef = make<OutputSectionCommand>(Name); + CmdRef = make<OutputSection>(Name, SHT_PROGBITS, 0); return CmdRef; } @@ -113,16 +106,56 @@ void LinkerScript::setDot(Expr E, const Twine &Loc, bool InSec) { uint64_t Val = E().getValue(); if (Val < Dot && InSec) error(Loc + ": unable to move location counter backward for: " + - CurAddressState->OutSec->Name); + Ctx->OutSec->Name); Dot = Val; + // Update to location counter means update to section size. if (InSec) - CurAddressState->OutSec->Size = Dot - CurAddressState->OutSec->Addr; + Ctx->OutSec->Size = Dot - Ctx->OutSec->Addr; } -// Sets value of a symbol. Two kinds of symbols are processed: synthetic -// symbols, whose value is an offset from beginning of section and regular -// symbols whose value is absolute. +// This function is called from processSectionCommands, +// while we are fixing the output section layout. +void LinkerScript::addSymbol(SymbolAssignment *Cmd) { + if (Cmd->Name == ".") + return; + + // If a symbol was in PROVIDE(), we need to define it only when + // it is a referenced undefined symbol. + Symbol *B = Symtab->find(Cmd->Name); + if (Cmd->Provide && (!B || B->isDefined())) + return; + + // Define a symbol. + Symbol *Sym; + uint8_t Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT; + std::tie(Sym, std::ignore) = Symtab->insert(Cmd->Name, /*Type*/ 0, Visibility, + /*CanOmitFromDynSym*/ false, + /*File*/ nullptr); + ExprValue Value = Cmd->Expression(); + SectionBase *Sec = Value.isAbsolute() ? nullptr : Value.Sec; + + // When this function is called, section addresses have not been + // fixed yet. So, we may or may not know the value of the RHS + // expression. + // + // For example, if an expression is `x = 42`, we know x is always 42. + // However, if an expression is `x = .`, there's no way to know its + // value at the moment. + // + // We want to set symbol values early if we can. This allows us to + // use symbols as variables in linker scripts. Doing so allows us to + // write expressions like this: `alignment = 16; . = ALIGN(., alignment)`. + uint64_t SymValue = Value.Sec ? 0 : Value.getValue(); + + replaceSymbol<Defined>(Sym, nullptr, Cmd->Name, STB_GLOBAL, Visibility, + STT_NOTYPE, SymValue, 0, Sec); + Cmd->Sym = cast<Defined>(Sym); +} + +// This function is called from assignAddresses, while we are +// fixing the output section addresses. This function is supposed +// to set the final value for a given symbol assignment. void LinkerScript::assignSymbol(SymbolAssignment *Cmd, bool InSec) { if (Cmd->Name == ".") { setDot(Cmd->Expression, Cmd->Location, InSec); @@ -132,116 +165,36 @@ void LinkerScript::assignSymbol(SymbolAssignment *Cmd, bool InSec) { if (!Cmd->Sym) return; - auto *Sym = cast<DefinedRegular>(Cmd->Sym); ExprValue V = Cmd->Expression(); if (V.isAbsolute()) { - Sym->Value = V.getValue(); + Cmd->Sym->Section = nullptr; + Cmd->Sym->Value = V.getValue(); } else { - Sym->Section = V.Sec; - Sym->Value = alignTo(V.Val, V.Alignment); - } -} - -static SymbolBody *findSymbol(StringRef S) { - switch (Config->EKind) { - case ELF32LEKind: - return Symtab<ELF32LE>::X->find(S); - case ELF32BEKind: - return Symtab<ELF32BE>::X->find(S); - case ELF64LEKind: - return Symtab<ELF64LE>::X->find(S); - case ELF64BEKind: - return Symtab<ELF64BE>::X->find(S); - default: - llvm_unreachable("unknown Config->EKind"); + Cmd->Sym->Section = V.Sec; + Cmd->Sym->Value = V.getSectionOffset(); } } -static SymbolBody *addRegularSymbol(SymbolAssignment *Cmd) { - switch (Config->EKind) { - case ELF32LEKind: - return addRegular<ELF32LE>(Cmd); - case ELF32BEKind: - return addRegular<ELF32BE>(Cmd); - case ELF64LEKind: - return addRegular<ELF64LE>(Cmd); - case ELF64BEKind: - return addRegular<ELF64BE>(Cmd); - default: - llvm_unreachable("unknown Config->EKind"); - } -} - -void LinkerScript::addSymbol(SymbolAssignment *Cmd) { - if (Cmd->Name == ".") - return; - - // If a symbol was in PROVIDE(), we need to define it only when - // it is a referenced undefined symbol. - SymbolBody *B = findSymbol(Cmd->Name); - if (Cmd->Provide && (!B || B->isDefined())) - return; - - Cmd->Sym = addRegularSymbol(Cmd); -} - -bool SymbolAssignment::classof(const BaseCommand *C) { - return C->Kind == AssignmentKind; -} - -bool OutputSectionCommand::classof(const BaseCommand *C) { - return C->Kind == OutputSectionKind; -} - -// Fill [Buf, Buf + Size) with Filler. -// This is used for linker script "=fillexp" command. -static void fill(uint8_t *Buf, size_t Size, uint32_t Filler) { - size_t I = 0; - for (; I + 4 < Size; I += 4) - memcpy(Buf + I, &Filler, 4); - memcpy(Buf + I, &Filler, Size - I); -} - -bool InputSectionDescription::classof(const BaseCommand *C) { - return C->Kind == InputSectionKind; -} - -bool AssertCommand::classof(const BaseCommand *C) { - return C->Kind == AssertKind; -} - -bool BytesDataCommand::classof(const BaseCommand *C) { - return C->Kind == BytesDataKind; -} - -static StringRef basename(InputSectionBase *S) { - if (S->File) - return sys::path::filename(S->File->getName()); - return ""; +static std::string getFilename(InputFile *File) { + if (!File) + return ""; + if (File->ArchiveName.empty()) + return File->getName(); + return (File->ArchiveName + "(" + File->getName() + ")").str(); } bool LinkerScript::shouldKeep(InputSectionBase *S) { - for (InputSectionDescription *ID : Opt.KeptSections) - if (ID->FilePat.match(basename(S))) + if (KeptSections.empty()) + return false; + std::string Filename = getFilename(S->File); + for (InputSectionDescription *ID : KeptSections) + if (ID->FilePat.match(Filename)) for (SectionPattern &P : ID->SectionPatterns) if (P.SectionPat.match(S->Name)) return true; return false; } -// If an input string is in the form of "foo.N" where N is a number, -// return N. Otherwise, returns 65536, which is one greater than the -// lowest priority. -static int getPriority(StringRef S) { - size_t Pos = S.rfind('.'); - if (Pos == StringRef::npos) - return 65536; - int V; - if (!to_integer(S.substr(Pos + 1), V, 10)) - return 65536; - return V; -} - // A helper function for the SORT() command. static std::function<bool(InputSectionBase *, InputSectionBase *)> getComparator(SortSectionPolicy K) { @@ -267,28 +220,63 @@ getComparator(SortSectionPolicy K) { } // A helper function for the SORT() command. -static bool matchConstraints(ArrayRef<InputSectionBase *> Sections, +static bool matchConstraints(ArrayRef<InputSection *> Sections, ConstraintKind Kind) { if (Kind == ConstraintKind::NoConstraint) return true; - bool IsRW = llvm::any_of(Sections, [](InputSectionBase *Sec) { - return static_cast<InputSectionBase *>(Sec)->Flags & SHF_WRITE; - }); + bool IsRW = llvm::any_of( + Sections, [](InputSection *Sec) { return Sec->Flags & SHF_WRITE; }); return (IsRW && Kind == ConstraintKind::ReadWrite) || (!IsRW && Kind == ConstraintKind::ReadOnly); } -static void sortSections(InputSection **Begin, InputSection **End, +static void sortSections(MutableArrayRef<InputSection *> Vec, SortSectionPolicy K) { if (K != SortSectionPolicy::Default && K != SortSectionPolicy::None) - std::stable_sort(Begin, End, getComparator(K)); + std::stable_sort(Vec.begin(), Vec.end(), getComparator(K)); +} + +// Sort sections as instructed by SORT-family commands and --sort-section +// option. Because SORT-family commands can be nested at most two depth +// (e.g. SORT_BY_NAME(SORT_BY_ALIGNMENT(.text.*))) and because the command +// line option is respected even if a SORT command is given, the exact +// behavior we have here is a bit complicated. Here are the rules. +// +// 1. If two SORT commands are given, --sort-section is ignored. +// 2. If one SORT command is given, and if it is not SORT_NONE, +// --sort-section is handled as an inner SORT command. +// 3. If one SORT command is given, and if it is SORT_NONE, don't sort. +// 4. If no SORT command is given, sort according to --sort-section. +// 5. If no SORT commands are given and --sort-section is not specified, +// apply sorting provided by --symbol-ordering-file if any exist. +static void sortInputSections( + MutableArrayRef<InputSection *> Vec, const SectionPattern &Pat, + const DenseMap<SectionBase *, int> &Order) { + if (Pat.SortOuter == SortSectionPolicy::None) + return; + + if (Pat.SortOuter == SortSectionPolicy::Default && + Config->SortSection == SortSectionPolicy::Default) { + // If -symbol-ordering-file was given, sort accordingly. + // Usually, Order is empty. + if (!Order.empty()) + sortByOrder(Vec, [&](InputSectionBase *S) { return Order.lookup(S); }); + return; + } + + if (Pat.SortInner == SortSectionPolicy::Default) + sortSections(Vec, Config->SortSection); + else + sortSections(Vec, Pat.SortInner); + sortSections(Vec, Pat.SortOuter); } // Compute and remember which sections the InputSectionDescription matches. std::vector<InputSection *> -LinkerScript::computeInputSections(const InputSectionDescription *Cmd) { +LinkerScript::computeInputSections(const InputSectionDescription *Cmd, + const DenseMap<SectionBase *, int> &Order) { std::vector<InputSection *> Ret; // Collects all sections that satisfy constraints of Cmd. @@ -296,13 +284,8 @@ LinkerScript::computeInputSections(const InputSectionDescription *Cmd) { size_t SizeBefore = Ret.size(); for (InputSectionBase *Sec : InputSections) { - if (Sec->Assigned) - continue; - - if (!Sec->Live) { - reportDiscarded(Sec); + if (!Sec->Live || Sec->Assigned) continue; - } // For -emit-relocs we have to ignore entries like // .rela.dyn : { *(.rela.data) } @@ -310,67 +293,51 @@ LinkerScript::computeInputSections(const InputSectionDescription *Cmd) { if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA) continue; - StringRef Filename = basename(Sec); + std::string Filename = getFilename(Sec->File); if (!Cmd->FilePat.match(Filename) || Pat.ExcludedFilePat.match(Filename) || !Pat.SectionPat.match(Sec->Name)) continue; + // It is safe to assume that Sec is an InputSection + // because mergeable or EH input sections have already been + // handled and eliminated. Ret.push_back(cast<InputSection>(Sec)); Sec->Assigned = true; } - // Sort sections as instructed by SORT-family commands and --sort-section - // option. Because SORT-family commands can be nested at most two depth - // (e.g. SORT_BY_NAME(SORT_BY_ALIGNMENT(.text.*))) and because the command - // line option is respected even if a SORT command is given, the exact - // behavior we have here is a bit complicated. Here are the rules. - // - // 1. If two SORT commands are given, --sort-section is ignored. - // 2. If one SORT command is given, and if it is not SORT_NONE, - // --sort-section is handled as an inner SORT command. - // 3. If one SORT command is given, and if it is SORT_NONE, don't sort. - // 4. If no SORT command is given, sort according to --sort-section. - InputSection **Begin = Ret.data() + SizeBefore; - InputSection **End = Ret.data() + Ret.size(); - if (Pat.SortOuter != SortSectionPolicy::None) { - if (Pat.SortInner == SortSectionPolicy::Default) - sortSections(Begin, End, Config->SortSection); - else - sortSections(Begin, End, Pat.SortInner); - sortSections(Begin, End, Pat.SortOuter); - } + sortInputSections(MutableArrayRef<InputSection *>(Ret).slice(SizeBefore), + Pat, Order); } return Ret; } -void LinkerScript::discard(ArrayRef<InputSectionBase *> V) { - for (InputSectionBase *S : V) { - S->Live = false; +void LinkerScript::discard(ArrayRef<InputSection *> V) { + for (InputSection *S : V) { if (S == InX::ShStrTab || S == InX::Dynamic || S == InX::DynSymTab || S == InX::DynStrTab) error("discarding " + S->Name + " section is not allowed"); + + S->Assigned = false; + S->Live = false; discard(S->DependentSections); } } -std::vector<InputSectionBase *> -LinkerScript::createInputSectionList(OutputSectionCommand &OutCmd) { - std::vector<InputSectionBase *> Ret; - - for (BaseCommand *Base : OutCmd.Commands) { - auto *Cmd = dyn_cast<InputSectionDescription>(Base); - if (!Cmd) - continue; +std::vector<InputSection *> LinkerScript::createInputSectionList( + OutputSection &OutCmd, const DenseMap<SectionBase *, int> &Order) { + std::vector<InputSection *> Ret; - Cmd->Sections = computeInputSections(Cmd); - Ret.insert(Ret.end(), Cmd->Sections.begin(), Cmd->Sections.end()); + for (BaseCommand *Base : OutCmd.SectionCommands) { + if (auto *Cmd = dyn_cast<InputSectionDescription>(Base)) { + Cmd->Sections = computeInputSections(Cmd, Order); + Ret.insert(Ret.end(), Cmd->Sections.begin(), Cmd->Sections.end()); + } } - return Ret; } -void LinkerScript::processCommands(OutputSectionFactory &Factory) { +void LinkerScript::processSectionCommands() { // A symbol can be assigned before any section is mentioned in the linker // script. In an DSO, the symbol values are addresses, so the only important // section values are: @@ -382,28 +349,31 @@ void LinkerScript::processCommands(OutputSectionFactory &Factory) { // which will map to whatever the first actual section is. Aether = make<OutputSection>("", 0, SHF_ALLOC); Aether->SectionIndex = 1; - auto State = make_unique<AddressState>(Opt); - // CurAddressState captures the local AddressState and makes it accessible - // deliberately. This is needed as there are some cases where we cannot just + + // Ctx captures the local AddressState and makes it accessible deliberately. + // This is needed as there are some cases where we cannot just // thread the current state through to a lambda function created by the // script parser. - CurAddressState = State.get(); - CurAddressState->OutSec = Aether; - Dot = 0; + auto Deleter = make_unique<AddressState>(); + Ctx = Deleter.get(); + Ctx->OutSec = Aether; - for (size_t I = 0; I < Opt.Commands.size(); ++I) { + size_t I = 0; + DenseMap<SectionBase *, int> Order = buildSectionOrder(); + // Add input sections to output sections. + for (BaseCommand *Base : SectionCommands) { // Handle symbol assignments outside of any output section. - if (auto *Cmd = dyn_cast<SymbolAssignment>(Opt.Commands[I])) { + if (auto *Cmd = dyn_cast<SymbolAssignment>(Base)) { addSymbol(Cmd); continue; } - if (auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I])) { - std::vector<InputSectionBase *> V = createInputSectionList(*Cmd); + if (auto *Sec = dyn_cast<OutputSection>(Base)) { + std::vector<InputSection *> V = createInputSectionList(*Sec, Order); // The output section name `/DISCARD/' is special. // Any input section assigned to it is discarded. - if (Cmd->Name == "/DISCARD/") { + if (Sec->Name == "/DISCARD/") { discard(V); continue; } @@ -413,250 +383,265 @@ void LinkerScript::processCommands(OutputSectionFactory &Factory) { // sections satisfy a given constraint. If not, a directive is handled // as if it wasn't present from the beginning. // - // Because we'll iterate over Commands many more times, the easiest - // way to "make it as if it wasn't present" is to just remove it. - if (!matchConstraints(V, Cmd->Constraint)) { + // Because we'll iterate over SectionCommands many more times, the easy + // way to "make it as if it wasn't present" is to make it empty. + if (!matchConstraints(V, Sec->Constraint)) { for (InputSectionBase *S : V) S->Assigned = false; - Opt.Commands.erase(Opt.Commands.begin() + I); - --I; + Sec->SectionCommands.clear(); continue; } // A directive may contain symbol definitions like this: // ".foo : { ...; bar = .; }". Handle them. - for (BaseCommand *Base : Cmd->Commands) + for (BaseCommand *Base : Sec->SectionCommands) if (auto *OutCmd = dyn_cast<SymbolAssignment>(Base)) addSymbol(OutCmd); // Handle subalign (e.g. ".foo : SUBALIGN(32) { ... }"). If subalign // is given, input sections are aligned to that value, whether the // given value is larger or smaller than the original section alignment. - if (Cmd->SubalignExpr) { - uint32_t Subalign = Cmd->SubalignExpr().getValue(); + if (Sec->SubalignExpr) { + uint32_t Subalign = Sec->SubalignExpr().getValue(); for (InputSectionBase *S : V) S->Alignment = Subalign; } // Add input sections to an output section. - for (InputSectionBase *S : V) - Factory.addInputSec(S, Cmd->Name, Cmd->Sec); - if (OutputSection *Sec = Cmd->Sec) { - assert(Sec->SectionIndex == INT_MAX); - Sec->SectionIndex = I; - if (Cmd->Noload) - Sec->Type = SHT_NOBITS; - SecToCommand[Sec] = Cmd; - } + for (InputSection *S : V) + Sec->addSection(S); + + Sec->SectionIndex = I++; + if (Sec->Noload) + Sec->Type = SHT_NOBITS; } } - CurAddressState = nullptr; + Ctx = nullptr; } -void LinkerScript::fabricateDefaultCommands() { - std::vector<BaseCommand *> Commands; - - // Define start address - uint64_t StartAddr = -1; - - // The Sections with -T<section> have been sorted in order of ascending - // address. We must lower StartAddr if the lowest -T<section address> as - // calls to setDot() must be monotonically increasing. - for (auto &KV : Config->SectionStartMap) - StartAddr = std::min(StartAddr, KV.second); - - Commands.push_back(make<SymbolAssignment>( - ".", - [=] { - return std::min(StartAddr, Config->ImageBase + elf::getHeaderSize()); - }, - "")); +static OutputSection *findByName(ArrayRef<BaseCommand *> Vec, + StringRef Name) { + for (BaseCommand *Base : Vec) + if (auto *Sec = dyn_cast<OutputSection>(Base)) + if (Sec->Name == Name) + return Sec; + return nullptr; +} - // For each OutputSection that needs a VA fabricate an OutputSectionCommand - // with an InputSectionDescription describing the InputSections - for (OutputSection *Sec : OutputSections) { - auto *OSCmd = createOutputSectionCommand(Sec->Name, "<internal>"); - OSCmd->Sec = Sec; - SecToCommand[Sec] = OSCmd; - - Commands.push_back(OSCmd); - if (Sec->Sections.size()) { - auto *ISD = make<InputSectionDescription>(""); - OSCmd->Commands.push_back(ISD); - for (InputSection *ISec : Sec->Sections) { - ISD->Sections.push_back(ISec); - ISec->Assigned = true; - } +static OutputSection *createSection(InputSectionBase *IS, + StringRef OutsecName) { + OutputSection *Sec = Script->createOutputSection(OutsecName, "<internal>"); + Sec->addSection(cast<InputSection>(IS)); + return Sec; +} + +static OutputSection *addInputSec(StringMap<OutputSection *> &Map, + InputSectionBase *IS, StringRef OutsecName) { + // Sections with SHT_GROUP or SHF_GROUP attributes reach here only when the -r + // option is given. A section with SHT_GROUP defines a "section group", and + // its members have SHF_GROUP attribute. Usually these flags have already been + // stripped by InputFiles.cpp as section groups are processed and uniquified. + // However, for the -r option, we want to pass through all section groups + // as-is because adding/removing members or merging them with other groups + // change their semantics. + if (IS->Type == SHT_GROUP || (IS->Flags & SHF_GROUP)) + return createSection(IS, OutsecName); + + // Imagine .zed : { *(.foo) *(.bar) } script. Both foo and bar may have + // relocation sections .rela.foo and .rela.bar for example. Most tools do + // not allow multiple REL[A] sections for output section. Hence we + // should combine these relocation sections into single output. + // We skip synthetic sections because it can be .rela.dyn/.rela.plt or any + // other REL[A] sections created by linker itself. + if (!isa<SyntheticSection>(IS) && + (IS->Type == SHT_REL || IS->Type == SHT_RELA)) { + auto *Sec = cast<InputSection>(IS); + OutputSection *Out = Sec->getRelocatedSection()->getOutputSection(); + + if (Out->RelocationSection) { + Out->RelocationSection->addSection(Sec); + return nullptr; } + + Out->RelocationSection = createSection(IS, OutsecName); + return Out->RelocationSection; + } + + // When control reaches here, mergeable sections have already been merged into + // synthetic sections. For relocatable case we want to create one output + // section per syntetic section so that they have a valid sh_entsize. + if (Config->Relocatable && (IS->Flags & SHF_MERGE)) + return createSection(IS, OutsecName); + + // The ELF spec just says + // ---------------------------------------------------------------- + // In the first phase, input sections that match in name, type and + // attribute flags should be concatenated into single sections. + // ---------------------------------------------------------------- + // + // However, it is clear that at least some flags have to be ignored for + // section merging. At the very least SHF_GROUP and SHF_COMPRESSED have to be + // ignored. We should not have two output .text sections just because one was + // in a group and another was not for example. + // + // It also seems that that wording was a late addition and didn't get the + // necessary scrutiny. + // + // Merging sections with different flags is expected by some users. One + // reason is that if one file has + // + // int *const bar __attribute__((section(".foo"))) = (int *)0; + // + // gcc with -fPIC will produce a read only .foo section. But if another + // file has + // + // int zed; + // int *const bar __attribute__((section(".foo"))) = (int *)&zed; + // + // gcc with -fPIC will produce a read write section. + // + // Last but not least, when using linker script the merge rules are forced by + // the script. Unfortunately, linker scripts are name based. This means that + // expressions like *(.foo*) can refer to multiple input sections with + // different flags. We cannot put them in different output sections or we + // would produce wrong results for + // + // start = .; *(.foo.*) end = .; *(.bar) + // + // and a mapping of .foo1 and .bar1 to one section and .foo2 and .bar2 to + // another. The problem is that there is no way to layout those output + // sections such that the .foo sections are the only thing between the start + // and end symbols. + // + // Given the above issues, we instead merge sections by name and error on + // incompatible types and flags. + OutputSection *&Sec = Map[OutsecName]; + if (Sec) { + Sec->addSection(cast<InputSection>(IS)); + return nullptr; } - // SECTIONS commands run before other non SECTIONS commands - Commands.insert(Commands.end(), Opt.Commands.begin(), Opt.Commands.end()); - Opt.Commands = std::move(Commands); + + Sec = createSection(IS, OutsecName); + return Sec; } // Add sections that didn't match any sections command. -void LinkerScript::addOrphanSections(OutputSectionFactory &Factory) { - unsigned NumCommands = Opt.Commands.size(); +void LinkerScript::addOrphanSections() { + unsigned End = SectionCommands.size(); + StringMap<OutputSection *> Map; + + std::vector<OutputSection *> V; for (InputSectionBase *S : InputSections) { if (!S->Live || S->Parent) continue; - StringRef Name = getOutputSectionName(S->Name); - auto End = Opt.Commands.begin() + NumCommands; - auto I = std::find_if(Opt.Commands.begin(), End, [&](BaseCommand *Base) { - if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base)) - return Cmd->Name == Name; - return false; - }); - OutputSectionCommand *Cmd; - if (I == End) { - Factory.addInputSec(S, Name); - OutputSection *Sec = S->getOutputSection(); - assert(Sec->SectionIndex == INT_MAX); - OutputSectionCommand *&CmdRef = SecToCommand[Sec]; - if (!CmdRef) { - CmdRef = createOutputSectionCommand(Sec->Name, "<internal>"); - CmdRef->Sec = Sec; - Opt.Commands.push_back(CmdRef); - } - Cmd = CmdRef; - } else { - Cmd = cast<OutputSectionCommand>(*I); - Factory.addInputSec(S, Name, Cmd->Sec); - if (OutputSection *Sec = Cmd->Sec) { - SecToCommand[Sec] = Cmd; - unsigned Index = std::distance(Opt.Commands.begin(), I); - assert(Sec->SectionIndex == INT_MAX || Sec->SectionIndex == Index); - Sec->SectionIndex = Index; - } + + StringRef Name = getOutputSectionName(S); + + if (Config->OrphanHandling == OrphanHandlingPolicy::Error) + error(toString(S) + " is being placed in '" + Name + "'"); + else if (Config->OrphanHandling == OrphanHandlingPolicy::Warn) + warn(toString(S) + " is being placed in '" + Name + "'"); + + if (OutputSection *Sec = + findByName(makeArrayRef(SectionCommands).slice(0, End), Name)) { + Sec->addSection(cast<InputSection>(S)); + continue; } - auto *ISD = make<InputSectionDescription>(""); - ISD->Sections.push_back(cast<InputSection>(S)); - Cmd->Commands.push_back(ISD); + + if (OutputSection *OS = addInputSec(Map, S, Name)) + V.push_back(OS); + assert(S->getOutputSection()->SectionIndex == INT_MAX); } + + // If no SECTIONS command was given, we should insert sections commands + // before others, so that we can handle scripts which refers them, + // for example: "foo = ABSOLUTE(ADDR(.text)));". + // When SECTIONS command is present we just add all orphans to the end. + if (HasSectionsCommand) + SectionCommands.insert(SectionCommands.end(), V.begin(), V.end()); + else + SectionCommands.insert(SectionCommands.begin(), V.begin(), V.end()); } -uint64_t LinkerScript::advance(uint64_t Size, unsigned Align) { - bool IsTbss = (CurAddressState->OutSec->Flags & SHF_TLS) && - CurAddressState->OutSec->Type == SHT_NOBITS; - uint64_t Start = IsTbss ? Dot + CurAddressState->ThreadBssOffset : Dot; - Start = alignTo(Start, Align); +uint64_t LinkerScript::advance(uint64_t Size, unsigned Alignment) { + bool IsTbss = + (Ctx->OutSec->Flags & SHF_TLS) && Ctx->OutSec->Type == SHT_NOBITS; + uint64_t Start = IsTbss ? Dot + Ctx->ThreadBssOffset : Dot; + Start = alignTo(Start, Alignment); uint64_t End = Start + Size; if (IsTbss) - CurAddressState->ThreadBssOffset = End - Dot; + Ctx->ThreadBssOffset = End - Dot; else Dot = End; return End; } void LinkerScript::output(InputSection *S) { + uint64_t Before = advance(0, 1); uint64_t Pos = advance(S->getSize(), S->Alignment); - S->OutSecOff = Pos - S->getSize() - CurAddressState->OutSec->Addr; + S->OutSecOff = Pos - S->getSize() - Ctx->OutSec->Addr; // Update output section size after adding each section. This is so that // SIZEOF works correctly in the case below: // .foo { *(.aaa) a = SIZEOF(.foo); *(.bbb) } - CurAddressState->OutSec->Size = Pos - CurAddressState->OutSec->Addr; + Ctx->OutSec->Size = Pos - Ctx->OutSec->Addr; // If there is a memory region associated with this input section, then // place the section in that region and update the region index. - if (CurAddressState->MemRegion) { - uint64_t &CurOffset = - CurAddressState->MemRegionOffset[CurAddressState->MemRegion]; - CurOffset += CurAddressState->OutSec->Size; - uint64_t CurSize = CurOffset - CurAddressState->MemRegion->Origin; - if (CurSize > CurAddressState->MemRegion->Length) { - uint64_t OverflowAmt = CurSize - CurAddressState->MemRegion->Length; - error("section '" + CurAddressState->OutSec->Name + - "' will not fit in region '" + CurAddressState->MemRegion->Name + - "': overflowed by " + Twine(OverflowAmt) + " bytes"); + if (Ctx->MemRegion) { + uint64_t &CurOffset = Ctx->MemRegionOffset[Ctx->MemRegion]; + CurOffset += Pos - Before; + uint64_t CurSize = CurOffset - Ctx->MemRegion->Origin; + if (CurSize > Ctx->MemRegion->Length) { + uint64_t OverflowAmt = CurSize - Ctx->MemRegion->Length; + error("section '" + Ctx->OutSec->Name + "' will not fit in region '" + + Ctx->MemRegion->Name + "': overflowed by " + Twine(OverflowAmt) + + " bytes"); } } } void LinkerScript::switchTo(OutputSection *Sec) { - if (CurAddressState->OutSec == Sec) + if (Ctx->OutSec == Sec) return; - CurAddressState->OutSec = Sec; - CurAddressState->OutSec->Addr = - advance(0, CurAddressState->OutSec->Alignment); + Ctx->OutSec = Sec; + Ctx->OutSec->Addr = advance(0, Ctx->OutSec->Alignment); // If neither AT nor AT> is specified for an allocatable section, the linker // will set the LMA such that the difference between VMA and LMA for the // section is the same as the preceding output section in the same region // https://sourceware.org/binutils/docs-2.20/ld/Output-Section-LMA.html - if (CurAddressState->LMAOffset) - CurAddressState->OutSec->LMAOffset = CurAddressState->LMAOffset(); -} - -void LinkerScript::process(BaseCommand &Base) { - // This handles the assignments to symbol or to the dot. - if (auto *Cmd = dyn_cast<SymbolAssignment>(&Base)) { - assignSymbol(Cmd, true); - return; - } - - // Handle BYTE(), SHORT(), LONG(), or QUAD(). - if (auto *Cmd = dyn_cast<BytesDataCommand>(&Base)) { - Cmd->Offset = Dot - CurAddressState->OutSec->Addr; - Dot += Cmd->Size; - CurAddressState->OutSec->Size = Dot - CurAddressState->OutSec->Addr; - return; - } - - // Handle ASSERT(). - if (auto *Cmd = dyn_cast<AssertCommand>(&Base)) { - Cmd->Expression(); - return; - } - - // Handle a single input section description command. - // It calculates and assigns the offsets for each section and also - // updates the output section size. - auto &Cmd = cast<InputSectionDescription>(Base); - for (InputSection *Sec : Cmd.Sections) { - // We tentatively added all synthetic sections at the beginning and removed - // empty ones afterwards (because there is no way to know whether they were - // going be empty or not other than actually running linker scripts.) - // We need to ignore remains of empty sections. - if (auto *S = dyn_cast<SyntheticSection>(Sec)) - if (S->empty()) - continue; - - if (!Sec->Live) - continue; - assert(CurAddressState->OutSec == Sec->getParent()); - output(Sec); - } + if (Ctx->LMAOffset) + Ctx->OutSec->LMAOffset = Ctx->LMAOffset(); } // This function searches for a memory region to place the given output // section in. If found, a pointer to the appropriate memory region is // returned. Otherwise, a nullptr is returned. -MemoryRegion *LinkerScript::findMemoryRegion(OutputSectionCommand *Cmd) { +MemoryRegion *LinkerScript::findMemoryRegion(OutputSection *Sec) { // If a memory region name was specified in the output section command, // then try to find that region first. - if (!Cmd->MemoryRegionName.empty()) { - auto It = Opt.MemoryRegions.find(Cmd->MemoryRegionName); - if (It != Opt.MemoryRegions.end()) - return &It->second; - error("memory region '" + Cmd->MemoryRegionName + "' not declared"); + if (!Sec->MemoryRegionName.empty()) { + auto It = MemoryRegions.find(Sec->MemoryRegionName); + if (It != MemoryRegions.end()) + return It->second; + error("memory region '" + Sec->MemoryRegionName + "' not declared"); return nullptr; } // If at least one memory region is defined, all sections must // belong to some memory region. Otherwise, we don't need to do // anything for memory regions. - if (Opt.MemoryRegions.empty()) + if (MemoryRegions.empty()) return nullptr; - OutputSection *Sec = Cmd->Sec; // See if a region can be found by matching section flags. - for (auto &Pair : Opt.MemoryRegions) { - MemoryRegion &M = Pair.second; - if ((M.Flags & Sec->Flags) && (M.NegFlags & Sec->Flags) == 0) - return &M; + for (auto &Pair : MemoryRegions) { + MemoryRegion *M = Pair.second; + if ((M->Flags & Sec->Flags) && (M->NegFlags & Sec->Flags) == 0) + return M; } // Otherwise, no suitable region was found. @@ -667,33 +652,76 @@ MemoryRegion *LinkerScript::findMemoryRegion(OutputSectionCommand *Cmd) { // This function assigns offsets to input sections and an output section // for a single sections command (e.g. ".text { *(.text); }"). -void LinkerScript::assignOffsets(OutputSectionCommand *Cmd) { - OutputSection *Sec = Cmd->Sec; - if (!Sec) - return; - +void LinkerScript::assignOffsets(OutputSection *Sec) { if (!(Sec->Flags & SHF_ALLOC)) Dot = 0; - else if (Cmd->AddrExpr) - setDot(Cmd->AddrExpr, Cmd->Location, false); + else if (Sec->AddrExpr) + setDot(Sec->AddrExpr, Sec->Location, false); - if (Cmd->LMAExpr) { + Ctx->MemRegion = Sec->MemRegion; + if (Ctx->MemRegion) + Dot = Ctx->MemRegionOffset[Ctx->MemRegion]; + + if (Sec->LMAExpr) { uint64_t D = Dot; - CurAddressState->LMAOffset = [=] { return Cmd->LMAExpr().getValue() - D; }; + Ctx->LMAOffset = [=] { return Sec->LMAExpr().getValue() - D; }; } - CurAddressState->MemRegion = Cmd->MemRegion; - if (CurAddressState->MemRegion) - Dot = CurAddressState->MemRegionOffset[CurAddressState->MemRegion]; switchTo(Sec); // We do not support custom layout for compressed debug sectons. // At this point we already know their size and have compressed content. - if (CurAddressState->OutSec->Flags & SHF_COMPRESSED) + if (Ctx->OutSec->Flags & SHF_COMPRESSED) return; - for (BaseCommand *C : Cmd->Commands) - process(*C); + // The Size previously denoted how many InputSections had been added to this + // section, and was used for sorting SHF_LINK_ORDER sections. Reset it to + // compute the actual size value. + Sec->Size = 0; + + // We visited SectionsCommands from processSectionCommands to + // layout sections. Now, we visit SectionsCommands again to fix + // section offsets. + for (BaseCommand *Base : Sec->SectionCommands) { + // This handles the assignments to symbol or to the dot. + if (auto *Cmd = dyn_cast<SymbolAssignment>(Base)) { + assignSymbol(Cmd, true); + continue; + } + + // Handle BYTE(), SHORT(), LONG(), or QUAD(). + if (auto *Cmd = dyn_cast<ByteCommand>(Base)) { + Cmd->Offset = Dot - Ctx->OutSec->Addr; + Dot += Cmd->Size; + Ctx->OutSec->Size = Dot - Ctx->OutSec->Addr; + continue; + } + + // Handle ASSERT(). + if (auto *Cmd = dyn_cast<AssertCommand>(Base)) { + Cmd->Expression(); + continue; + } + + // Handle a single input section description command. + // It calculates and assigns the offsets for each section and also + // updates the output section size. + auto *Cmd = cast<InputSectionDescription>(Base); + for (InputSection *Sec : Cmd->Sections) { + // We tentatively added all synthetic sections at the beginning and + // removed empty ones afterwards (because there is no way to know + // whether they were going be empty or not other than actually running + // linker scripts.) We need to ignore remains of empty sections. + if (auto *S = dyn_cast<SyntheticSection>(Sec)) + if (S->empty()) + continue; + + if (!Sec->Live) + continue; + assert(Ctx->OutSec == Sec->getParent()); + output(Sec); + } + } } void LinkerScript::removeEmptyCommands() { @@ -703,17 +731,15 @@ void LinkerScript::removeEmptyCommands() { // clutter the output. // We instead remove trivially empty sections. The bfd linker seems even // more aggressive at removing them. - auto Pos = std::remove_if( - Opt.Commands.begin(), Opt.Commands.end(), [&](BaseCommand *Base) { - if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base)) - return Cmd->Sec == nullptr; - return false; - }); - Opt.Commands.erase(Pos, Opt.Commands.end()); + llvm::erase_if(SectionCommands, [&](BaseCommand *Base) { + if (auto *Sec = dyn_cast<OutputSection>(Base)) + return !Sec->Live; + return false; + }); } -static bool isAllSectionDescription(const OutputSectionCommand &Cmd) { - for (BaseCommand *Base : Cmd.Commands) +static bool isAllSectionDescription(const OutputSection &Cmd) { + for (BaseCommand *Base : Cmd.SectionCommands) if (!isa<InputSectionDescription>(*Base)) return false; return true; @@ -721,38 +747,55 @@ static bool isAllSectionDescription(const OutputSectionCommand &Cmd) { void LinkerScript::adjustSectionsBeforeSorting() { // If the output section contains only symbol assignments, create a - // corresponding output section. The bfd linker seems to only create them if - // '.' is assigned to, but creating these section should not have any bad - // consequeces and gives us a section to put the symbol in. + // corresponding output section. The issue is what to do with linker script + // like ".foo : { symbol = 42; }". One option would be to convert it to + // "symbol = 42;". That is, move the symbol out of the empty section + // description. That seems to be what bfd does for this simple case. The + // problem is that this is not completely general. bfd will give up and + // create a dummy section too if there is a ". = . + 1" inside the section + // for example. + // Given that we want to create the section, we have to worry what impact + // it will have on the link. For example, if we just create a section with + // 0 for flags, it would change which PT_LOADs are created. + // We could remember that that particular section is dummy and ignore it in + // other parts of the linker, but unfortunately there are quite a few places + // that would need to change: + // * The program header creation. + // * The orphan section placement. + // * The address assignment. + // The other option is to pick flags that minimize the impact the section + // will have on the rest of the linker. That is why we copy the flags from + // the previous sections. Only a few flags are needed to keep the impact low. uint64_t Flags = SHF_ALLOC; - for (int I = 0, E = Opt.Commands.size(); I != E; ++I) { - auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I]); - if (!Cmd) + for (BaseCommand *Cmd : SectionCommands) { + auto *Sec = dyn_cast<OutputSection>(Cmd); + if (!Sec) continue; - if (OutputSection *Sec = Cmd->Sec) { - Flags = Sec->Flags; + if (Sec->Live) { + Flags = Sec->Flags & (SHF_ALLOC | SHF_WRITE | SHF_EXECINSTR); continue; } - if (isAllSectionDescription(*Cmd)) + if (isAllSectionDescription(*Sec)) continue; - auto *OutSec = make<OutputSection>(Cmd->Name, SHT_PROGBITS, Flags); - OutSec->SectionIndex = I; - Cmd->Sec = OutSec; - SecToCommand[OutSec] = Cmd; + Sec->Live = true; + Sec->Flags = Flags; } } void LinkerScript::adjustSectionsAfterSorting() { // Try and find an appropriate memory region to assign offsets in. - for (BaseCommand *Base : Opt.Commands) { - if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base)) { - Cmd->MemRegion = findMemoryRegion(Cmd); + for (BaseCommand *Base : SectionCommands) { + if (auto *Sec = dyn_cast<OutputSection>(Base)) { + if (!Sec->Live) + continue; + Sec->MemRegion = findMemoryRegion(Sec); // Handle align (e.g. ".foo : ALIGN(16) { ... }"). - if (Cmd->AlignExpr) - Cmd->Sec->updateAlignment(Cmd->AlignExpr().getValue()); + if (Sec->AlignExpr) + Sec->Alignment = + std::max<uint32_t>(Sec->Alignment, Sec->AlignExpr().getValue()); } } @@ -764,108 +807,112 @@ void LinkerScript::adjustSectionsAfterSorting() { // SECTIONS { .aaa : { *(.aaa) } } std::vector<StringRef> DefPhdrs; auto FirstPtLoad = - std::find_if(Opt.PhdrsCommands.begin(), Opt.PhdrsCommands.end(), + std::find_if(PhdrsCommands.begin(), PhdrsCommands.end(), [](const PhdrsCommand &Cmd) { return Cmd.Type == PT_LOAD; }); - if (FirstPtLoad != Opt.PhdrsCommands.end()) + if (FirstPtLoad != PhdrsCommands.end()) DefPhdrs.push_back(FirstPtLoad->Name); // Walk the commands and propagate the program headers to commands that don't // explicitly specify them. - for (BaseCommand *Base : Opt.Commands) { - auto *Cmd = dyn_cast<OutputSectionCommand>(Base); - if (!Cmd) + for (BaseCommand *Base : SectionCommands) { + auto *Sec = dyn_cast<OutputSection>(Base); + if (!Sec) continue; - if (Cmd->Phdrs.empty()) { - OutputSection *Sec = Cmd->Sec; + if (Sec->Phdrs.empty()) { // To match the bfd linker script behaviour, only propagate program // headers to sections that are allocated. - if (Sec && (Sec->Flags & SHF_ALLOC)) - Cmd->Phdrs = DefPhdrs; + if (Sec->Flags & SHF_ALLOC) + Sec->Phdrs = DefPhdrs; } else { - DefPhdrs = Cmd->Phdrs; + DefPhdrs = Sec->Phdrs; } } - - removeEmptyCommands(); } -void LinkerScript::processNonSectionCommands() { - for (BaseCommand *Base : Opt.Commands) { - if (auto *Cmd = dyn_cast<SymbolAssignment>(Base)) - assignSymbol(Cmd, false); - else if (auto *Cmd = dyn_cast<AssertCommand>(Base)) - Cmd->Expression(); - } +static OutputSection *findFirstSection(PhdrEntry *Load) { + for (OutputSection *Sec : OutputSections) + if (Sec->PtLoad == Load) + return Sec; + return nullptr; } -void LinkerScript::allocateHeaders(std::vector<PhdrEntry> &Phdrs) { +// Try to find an address for the file and program headers output sections, +// which were unconditionally added to the first PT_LOAD segment earlier. +// +// When using the default layout, we check if the headers fit below the first +// allocated section. When using a linker script, we also check if the headers +// are covered by the output section. This allows omitting the headers by not +// leaving enough space for them in the linker script; this pattern is common +// in embedded systems. +// +// If there isn't enough space for these sections, we'll remove them from the +// PT_LOAD segment, and we'll also remove the PT_PHDR segment. +void LinkerScript::allocateHeaders(std::vector<PhdrEntry *> &Phdrs) { uint64_t Min = std::numeric_limits<uint64_t>::max(); - for (OutputSectionCommand *Cmd : OutputSectionCommands) { - OutputSection *Sec = Cmd->Sec; + for (OutputSection *Sec : OutputSections) if (Sec->Flags & SHF_ALLOC) Min = std::min<uint64_t>(Min, Sec->Addr); - } - auto FirstPTLoad = llvm::find_if( - Phdrs, [](const PhdrEntry &E) { return E.p_type == PT_LOAD; }); - if (FirstPTLoad == Phdrs.end()) + auto It = llvm::find_if( + Phdrs, [](const PhdrEntry *E) { return E->p_type == PT_LOAD; }); + if (It == Phdrs.end()) return; + PhdrEntry *FirstPTLoad = *It; uint64_t HeaderSize = getHeaderSize(); - if (HeaderSize <= Min || Script->hasPhdrsCommands()) { + // When linker script with SECTIONS is being used, don't output headers + // unless there's a space for them. + uint64_t Base = HasSectionsCommand ? alignDown(Min, Config->MaxPageSize) : 0; + if (HeaderSize <= Min - Base || Script->hasPhdrsCommands()) { Min = alignDown(Min - HeaderSize, Config->MaxPageSize); Out::ElfHeader->Addr = Min; Out::ProgramHeaders->Addr = Min + Out::ElfHeader->Size; return; } - assert(FirstPTLoad->First == Out::ElfHeader); - OutputSection *ActualFirst = nullptr; - for (OutputSectionCommand *Cmd : OutputSectionCommands) { - OutputSection *Sec = Cmd->Sec; - if (Sec->FirstInPtLoad == Out::ElfHeader) { - ActualFirst = Sec; - break; - } - } - if (ActualFirst) { - for (OutputSectionCommand *Cmd : OutputSectionCommands) { - OutputSection *Sec = Cmd->Sec; - if (Sec->FirstInPtLoad == Out::ElfHeader) - Sec->FirstInPtLoad = ActualFirst; - } - FirstPTLoad->First = ActualFirst; - } else { - Phdrs.erase(FirstPTLoad); - } + Out::ElfHeader->PtLoad = nullptr; + Out::ProgramHeaders->PtLoad = nullptr; + FirstPTLoad->FirstSec = findFirstSection(FirstPTLoad); - auto PhdrI = llvm::find_if( - Phdrs, [](const PhdrEntry &E) { return E.p_type == PT_PHDR; }); - if (PhdrI != Phdrs.end()) - Phdrs.erase(PhdrI); + llvm::erase_if(Phdrs, + [](const PhdrEntry *E) { return E->p_type == PT_PHDR; }); } -LinkerScript::AddressState::AddressState(const ScriptConfiguration &Opt) { - for (auto &MRI : Opt.MemoryRegions) { - const MemoryRegion *MR = &MRI.second; +LinkerScript::AddressState::AddressState() { + for (auto &MRI : Script->MemoryRegions) { + const MemoryRegion *MR = MRI.second; MemRegionOffset[MR] = MR->Origin; } } +static uint64_t getInitialDot() { + // By default linker scripts use an initial value of 0 for '.', + // but prefer -image-base if set. + if (Script->HasSectionsCommand) + return Config->ImageBase ? *Config->ImageBase : 0; + + uint64_t StartAddr = UINT64_MAX; + // The Sections with -T<section> have been sorted in order of ascending + // address. We must lower StartAddr if the lowest -T<section address> as + // calls to setDot() must be monotonically increasing. + for (auto &KV : Config->SectionStartMap) + StartAddr = std::min(StartAddr, KV.second); + return std::min(StartAddr, Target->getImageBase() + elf::getHeaderSize()); +} + +// Here we assign addresses as instructed by linker script SECTIONS +// sub-commands. Doing that allows us to use final VA values, so here +// we also handle rest commands like symbol assignments and ASSERTs. void LinkerScript::assignAddresses() { - // Assign addresses as instructed by linker script SECTIONS sub-commands. - Dot = 0; - auto State = make_unique<AddressState>(Opt); - // CurAddressState captures the local AddressState and makes it accessible - // deliberately. This is needed as there are some cases where we cannot just - // thread the current state through to a lambda function created by the - // script parser. - CurAddressState = State.get(); + Dot = getInitialDot(); + + auto Deleter = make_unique<AddressState>(); + Ctx = Deleter.get(); ErrorOnMissingSection = true; switchTo(Aether); - for (BaseCommand *Base : Opt.Commands) { + for (BaseCommand *Base : SectionCommands) { if (auto *Cmd = dyn_cast<SymbolAssignment>(Base)) { assignSymbol(Cmd, false); continue; @@ -876,380 +923,98 @@ void LinkerScript::assignAddresses() { continue; } - auto *Cmd = cast<OutputSectionCommand>(Base); - assignOffsets(Cmd); + assignOffsets(cast<OutputSection>(Base)); } - CurAddressState = nullptr; + Ctx = nullptr; } // Creates program headers as instructed by PHDRS linker script command. -std::vector<PhdrEntry> LinkerScript::createPhdrs() { - std::vector<PhdrEntry> Ret; +std::vector<PhdrEntry *> LinkerScript::createPhdrs() { + std::vector<PhdrEntry *> Ret; // Process PHDRS and FILEHDR keywords because they are not // real output sections and cannot be added in the following loop. - for (const PhdrsCommand &Cmd : Opt.PhdrsCommands) { - Ret.emplace_back(Cmd.Type, Cmd.Flags == UINT_MAX ? PF_R : Cmd.Flags); - PhdrEntry &Phdr = Ret.back(); + for (const PhdrsCommand &Cmd : PhdrsCommands) { + PhdrEntry *Phdr = make<PhdrEntry>(Cmd.Type, Cmd.Flags ? *Cmd.Flags : PF_R); if (Cmd.HasFilehdr) - Phdr.add(Out::ElfHeader); + Phdr->add(Out::ElfHeader); if (Cmd.HasPhdrs) - Phdr.add(Out::ProgramHeaders); + Phdr->add(Out::ProgramHeaders); if (Cmd.LMAExpr) { - Phdr.p_paddr = Cmd.LMAExpr().getValue(); - Phdr.HasLMA = true; + Phdr->p_paddr = Cmd.LMAExpr().getValue(); + Phdr->HasLMA = true; } + Ret.push_back(Phdr); } // Add output sections to program headers. - for (OutputSectionCommand *Cmd : OutputSectionCommands) { + for (OutputSection *Sec : OutputSections) { // Assign headers specified by linker script - for (size_t Id : getPhdrIndices(Cmd)) { - OutputSection *Sec = Cmd->Sec; - Ret[Id].add(Sec); - if (Opt.PhdrsCommands[Id].Flags == UINT_MAX) - Ret[Id].p_flags |= Sec->getPhdrFlags(); + for (size_t Id : getPhdrIndices(Sec)) { + Ret[Id]->add(Sec); + if (!PhdrsCommands[Id].Flags.hasValue()) + Ret[Id]->p_flags |= Sec->getPhdrFlags(); } } return Ret; } -bool LinkerScript::ignoreInterpSection() { - // Ignore .interp section in case we have PHDRS specification - // and PT_INTERP isn't listed. - if (Opt.PhdrsCommands.empty()) - return false; - for (PhdrsCommand &Cmd : Opt.PhdrsCommands) - if (Cmd.Type == PT_INTERP) - return false; - return true; -} - -OutputSectionCommand *LinkerScript::getCmd(OutputSection *Sec) const { - auto I = SecToCommand.find(Sec); - if (I == SecToCommand.end()) - return nullptr; - return I->second; -} - -void OutputSectionCommand::sort(std::function<int(InputSectionBase *S)> Order) { - typedef std::pair<unsigned, InputSection *> Pair; - auto Comp = [](const Pair &A, const Pair &B) { return A.first < B.first; }; - - std::vector<Pair> V; - assert(Commands.size() == 1); - auto *ISD = cast<InputSectionDescription>(Commands[0]); - for (InputSection *S : ISD->Sections) - V.push_back({Order(S), S}); - std::stable_sort(V.begin(), V.end(), Comp); - ISD->Sections.clear(); - for (Pair &P : V) - ISD->Sections.push_back(P.second); -} - -// Returns true if S matches /Filename.?\.o$/. -static bool isCrtBeginEnd(StringRef S, StringRef Filename) { - if (!S.endswith(".o")) - return false; - S = S.drop_back(2); - if (S.endswith(Filename)) - return true; - return !S.empty() && S.drop_back().endswith(Filename); -} - -static bool isCrtbegin(StringRef S) { return isCrtBeginEnd(S, "crtbegin"); } -static bool isCrtend(StringRef S) { return isCrtBeginEnd(S, "crtend"); } - -// .ctors and .dtors are sorted by this priority from highest to lowest. -// -// 1. The section was contained in crtbegin (crtbegin contains -// some sentinel value in its .ctors and .dtors so that the runtime -// can find the beginning of the sections.) -// -// 2. The section has an optional priority value in the form of ".ctors.N" -// or ".dtors.N" where N is a number. Unlike .{init,fini}_array, -// they are compared as string rather than number. -// -// 3. The section is just ".ctors" or ".dtors". +// Returns true if we should emit an .interp section. // -// 4. The section was contained in crtend, which contains an end marker. -// -// In an ideal world, we don't need this function because .init_array and -// .ctors are duplicate features (and .init_array is newer.) However, there -// are too many real-world use cases of .ctors, so we had no choice to -// support that with this rather ad-hoc semantics. -static bool compCtors(const InputSection *A, const InputSection *B) { - bool BeginA = isCrtbegin(A->File->getName()); - bool BeginB = isCrtbegin(B->File->getName()); - if (BeginA != BeginB) - return BeginA; - bool EndA = isCrtend(A->File->getName()); - bool EndB = isCrtend(B->File->getName()); - if (EndA != EndB) - return EndB; - StringRef X = A->Name; - StringRef Y = B->Name; - assert(X.startswith(".ctors") || X.startswith(".dtors")); - assert(Y.startswith(".ctors") || Y.startswith(".dtors")); - X = X.substr(6); - Y = Y.substr(6); - if (X.empty() && Y.empty()) - return false; - return X < Y; -} - -// Sorts input sections by the special rules for .ctors and .dtors. -// Unfortunately, the rules are different from the one for .{init,fini}_array. -// Read the comment above. -void OutputSectionCommand::sortCtorsDtors() { - assert(Commands.size() == 1); - auto *ISD = cast<InputSectionDescription>(Commands[0]); - std::stable_sort(ISD->Sections.begin(), ISD->Sections.end(), compCtors); -} - -// Sorts input sections by section name suffixes, so that .foo.N comes -// before .foo.M if N < M. Used to sort .{init,fini}_array.N sections. -// We want to keep the original order if the priorities are the same -// because the compiler keeps the original initialization order in a -// translation unit and we need to respect that. -// For more detail, read the section of the GCC's manual about init_priority. -void OutputSectionCommand::sortInitFini() { - // Sort sections by priority. - sort([](InputSectionBase *S) { return getPriority(S->Name); }); -} - -uint32_t OutputSectionCommand::getFiller() { - if (Filler) - return *Filler; - if (Sec->Flags & SHF_EXECINSTR) - return Target->TrapInstr; - return 0; -} - -static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) { - if (Size == 1) - *Buf = Data; - else if (Size == 2) - write16(Buf, Data, Config->Endianness); - else if (Size == 4) - write32(Buf, Data, Config->Endianness); - else if (Size == 8) - write64(Buf, Data, Config->Endianness); - else - llvm_unreachable("unsupported Size argument"); -} - -static bool compareByFilePosition(InputSection *A, InputSection *B) { - // Synthetic doesn't have link order dependecy, stable_sort will keep it last - if (A->kind() == InputSectionBase::Synthetic || - B->kind() == InputSectionBase::Synthetic) - return false; - InputSection *LA = A->getLinkOrderDep(); - InputSection *LB = B->getLinkOrderDep(); - OutputSection *AOut = LA->getParent(); - OutputSection *BOut = LB->getParent(); - if (AOut != BOut) - return AOut->SectionIndex < BOut->SectionIndex; - return LA->OutSecOff < LB->OutSecOff; -} - -template <class ELFT> -static void finalizeShtGroup(OutputSection *OS, - ArrayRef<InputSection *> Sections) { - assert(Config->Relocatable && Sections.size() == 1); - - // sh_link field for SHT_GROUP sections should contain the section index of - // the symbol table. - OS->Link = InX::SymTab->getParent()->SectionIndex; - - // sh_info then contain index of an entry in symbol table section which - // provides signature of the section group. - elf::ObjectFile<ELFT> *Obj = Sections[0]->getFile<ELFT>(); - ArrayRef<SymbolBody *> Symbols = Obj->getSymbols(); - OS->Info = InX::SymTab->getSymbolIndex(Symbols[Sections[0]->Info - 1]); +// We usually do. But if PHDRS commands are given, and +// no PT_INTERP is there, there's no place to emit an +// .interp, so we don't do that in that case. +bool LinkerScript::needsInterpSection() { + if (PhdrsCommands.empty()) + return true; + for (PhdrsCommand &Cmd : PhdrsCommands) + if (Cmd.Type == PT_INTERP) + return true; + return false; } -template <class ELFT> void OutputSectionCommand::finalize() { - // Link order may be distributed across several InputSectionDescriptions - // but sort must consider them all at once. - std::vector<InputSection **> ScriptSections; - std::vector<InputSection *> Sections; - for (BaseCommand *Base : Commands) - if (auto *ISD = dyn_cast<InputSectionDescription>(Base)) - for (InputSection *&IS : ISD->Sections) { - ScriptSections.push_back(&IS); - Sections.push_back(IS); - } - - if ((Sec->Flags & SHF_LINK_ORDER)) { - std::stable_sort(Sections.begin(), Sections.end(), compareByFilePosition); - for (int I = 0, N = Sections.size(); I < N; ++I) - *ScriptSections[I] = Sections[I]; - - // We must preserve the link order dependency of sections with the - // SHF_LINK_ORDER flag. The dependency is indicated by the sh_link field. We - // need to translate the InputSection sh_link to the OutputSection sh_link, - // all InputSections in the OutputSection have the same dependency. - if (auto *D = Sections.front()->getLinkOrderDep()) - Sec->Link = D->getParent()->SectionIndex; +ExprValue LinkerScript::getSymbolValue(StringRef Name, const Twine &Loc) { + if (Name == ".") { + if (Ctx) + return {Ctx->OutSec, false, Dot - Ctx->OutSec->Addr, Loc}; + error(Loc + ": unable to get location counter value"); + return 0; } - uint32_t Type = Sec->Type; - if (Type == SHT_GROUP) { - finalizeShtGroup<ELFT>(Sec, Sections); - return; - } - - if (!Config->CopyRelocs || (Type != SHT_RELA && Type != SHT_REL)) - return; - - InputSection *First = Sections[0]; - if (isa<SyntheticSection>(First)) - return; - - Sec->Link = InX::SymTab->getParent()->SectionIndex; - // sh_info for SHT_REL[A] sections should contain the section header index of - // the section to which the relocation applies. - InputSectionBase *S = First->getRelocatedSection(); - Sec->Info = S->getOutputSection()->SectionIndex; - Sec->Flags |= SHF_INFO_LINK; -} - -// Compress section contents if this section contains debug info. -template <class ELFT> void OutputSectionCommand::maybeCompress() { - typedef typename ELFT::Chdr Elf_Chdr; - - // Compress only DWARF debug sections. - if (!Config->CompressDebugSections || (Sec->Flags & SHF_ALLOC) || - !Name.startswith(".debug_")) - return; - - // Create a section header. - Sec->ZDebugHeader.resize(sizeof(Elf_Chdr)); - auto *Hdr = reinterpret_cast<Elf_Chdr *>(Sec->ZDebugHeader.data()); - Hdr->ch_type = ELFCOMPRESS_ZLIB; - Hdr->ch_size = Sec->Size; - Hdr->ch_addralign = Sec->Alignment; - - // Write section contents to a temporary buffer and compress it. - std::vector<uint8_t> Buf(Sec->Size); - writeTo<ELFT>(Buf.data()); - if (Error E = zlib::compress(toStringRef(Buf), Sec->CompressedData)) - fatal("compress failed: " + llvm::toString(std::move(E))); - - // Update section headers. - Sec->Size = sizeof(Elf_Chdr) + Sec->CompressedData.size(); - Sec->Flags |= SHF_COMPRESSED; -} - -template <class ELFT> void OutputSectionCommand::writeTo(uint8_t *Buf) { - if (Sec->Type == SHT_NOBITS) - return; - - Sec->Loc = Buf; - - // If -compress-debug-section is specified and if this is a debug seciton, - // we've already compressed section contents. If that's the case, - // just write it down. - if (!Sec->CompressedData.empty()) { - memcpy(Buf, Sec->ZDebugHeader.data(), Sec->ZDebugHeader.size()); - memcpy(Buf + Sec->ZDebugHeader.size(), Sec->CompressedData.data(), - Sec->CompressedData.size()); - return; + if (Symbol *Sym = Symtab->find(Name)) { + if (auto *DS = dyn_cast<Defined>(Sym)) + return {DS->Section, false, DS->Value, Loc}; + if (auto *SS = dyn_cast<SharedSymbol>(Sym)) + if (!ErrorOnMissingSection || SS->CopyRelSec) + return {SS->CopyRelSec, false, 0, Loc}; } - // Write leading padding. - std::vector<InputSection *> Sections; - for (BaseCommand *Cmd : Commands) - if (auto *ISD = dyn_cast<InputSectionDescription>(Cmd)) - for (InputSection *IS : ISD->Sections) - if (IS->Live) - Sections.push_back(IS); - uint32_t Filler = getFiller(); - if (Filler) - fill(Buf, Sections.empty() ? Sec->Size : Sections[0]->OutSecOff, Filler); - - parallelForEachN(0, Sections.size(), [=](size_t I) { - InputSection *IS = Sections[I]; - IS->writeTo<ELFT>(Buf); - - // Fill gaps between sections. - if (Filler) { - uint8_t *Start = Buf + IS->OutSecOff + IS->getSize(); - uint8_t *End; - if (I + 1 == Sections.size()) - End = Buf + Sec->Size; - else - End = Buf + Sections[I + 1]->OutSecOff; - fill(Start, End - Start, Filler); - } - }); - - // Linker scripts may have BYTE()-family commands with which you - // can write arbitrary bytes to the output. Process them if any. - for (BaseCommand *Base : Commands) - if (auto *Data = dyn_cast<BytesDataCommand>(Base)) - writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size); -} - -ExprValue LinkerScript::getSymbolValue(const Twine &Loc, StringRef S) { - if (S == ".") - return {CurAddressState->OutSec, Dot - CurAddressState->OutSec->Addr, Loc}; - if (SymbolBody *B = findSymbol(S)) { - if (auto *D = dyn_cast<DefinedRegular>(B)) - return {D->Section, D->Value, Loc}; - if (auto *C = dyn_cast<DefinedCommon>(B)) - return {InX::Common, C->Offset, Loc}; - } - error(Loc + ": symbol not found: " + S); + error(Loc + ": symbol not found: " + Name); return 0; } -bool LinkerScript::isDefined(StringRef S) { return findSymbol(S) != nullptr; } - -static const size_t NoPhdr = -1; +// Returns the index of the segment named Name. +static Optional<size_t> getPhdrIndex(ArrayRef<PhdrsCommand> Vec, + StringRef Name) { + for (size_t I = 0; I < Vec.size(); ++I) + if (Vec[I].Name == Name) + return I; + return None; +} // Returns indices of ELF headers containing specific section. Each index is a // zero based number of ELF header listed within PHDRS {} script block. -std::vector<size_t> LinkerScript::getPhdrIndices(OutputSectionCommand *Cmd) { +std::vector<size_t> LinkerScript::getPhdrIndices(OutputSection *Cmd) { std::vector<size_t> Ret; - for (StringRef PhdrName : Cmd->Phdrs) { - size_t Index = getPhdrIndex(Cmd->Location, PhdrName); - if (Index != NoPhdr) - Ret.push_back(Index); - } - return Ret; -} -// Returns the index of the segment named PhdrName if found otherwise -// NoPhdr. When not found, if PhdrName is not the special case value 'NONE' -// (which can be used to explicitly specify that a section isn't assigned to a -// segment) then error. -size_t LinkerScript::getPhdrIndex(const Twine &Loc, StringRef PhdrName) { - size_t I = 0; - for (PhdrsCommand &Cmd : Opt.PhdrsCommands) { - if (Cmd.Name == PhdrName) - return I; - ++I; + for (StringRef S : Cmd->Phdrs) { + if (Optional<size_t> Idx = getPhdrIndex(PhdrsCommands, S)) + Ret.push_back(*Idx); + else if (S != "NONE") + error(Cmd->Location + ": section header '" + S + + "' is not listed in PHDRS"); } - if (PhdrName != "NONE") - error(Loc + ": section header '" + PhdrName + "' is not listed in PHDRS"); - return NoPhdr; + return Ret; } - -template void OutputSectionCommand::writeTo<ELF32LE>(uint8_t *Buf); -template void OutputSectionCommand::writeTo<ELF32BE>(uint8_t *Buf); -template void OutputSectionCommand::writeTo<ELF64LE>(uint8_t *Buf); -template void OutputSectionCommand::writeTo<ELF64BE>(uint8_t *Buf); - -template void OutputSectionCommand::maybeCompress<ELF32LE>(); -template void OutputSectionCommand::maybeCompress<ELF32BE>(); -template void OutputSectionCommand::maybeCompress<ELF64LE>(); -template void OutputSectionCommand::maybeCompress<ELF64BE>(); - -template void OutputSectionCommand::finalize<ELF32LE>(); -template void OutputSectionCommand::finalize<ELF32BE>(); -template void OutputSectionCommand::finalize<ELF64LE>(); -template void OutputSectionCommand::finalize<ELF64BE>(); |