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-rw-r--r--ELF/OutputSections.cpp488
1 files changed, 327 insertions, 161 deletions
diff --git a/ELF/OutputSections.cpp b/ELF/OutputSections.cpp
index abe548165866..f0677f7e1ca5 100644
--- a/ELF/OutputSections.cpp
+++ b/ELF/OutputSections.cpp
@@ -10,13 +10,14 @@
#include "OutputSections.h"
#include "Config.h"
#include "LinkerScript.h"
-#include "Memory.h"
#include "Strings.h"
#include "SymbolTable.h"
#include "SyntheticSections.h"
#include "Target.h"
-#include "Threads.h"
+#include "lld/Common/Memory.h"
+#include "lld/Common/Threads.h"
#include "llvm/BinaryFormat/Dwarf.h"
+#include "llvm/Support/Compression.h"
#include "llvm/Support/MD5.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/SHA1.h"
@@ -42,7 +43,6 @@ OutputSection *Out::InitArray;
OutputSection *Out::FiniArray;
std::vector<OutputSection *> elf::OutputSections;
-std::vector<OutputSectionCommand *> elf::OutputSectionCommands;
uint32_t OutputSection::getPhdrFlags() const {
uint32_t Ret = PF_R;
@@ -68,210 +68,376 @@ void OutputSection::writeHeaderTo(typename ELFT::Shdr *Shdr) {
}
OutputSection::OutputSection(StringRef Name, uint32_t Type, uint64_t Flags)
- : SectionBase(Output, Name, Flags, /*Entsize*/ 0, /*Alignment*/ 1, Type,
+ : BaseCommand(OutputSectionKind),
+ SectionBase(Output, Name, Flags, /*Entsize*/ 0, /*Alignment*/ 1, Type,
/*Info*/ 0,
/*Link*/ 0),
- SectionIndex(INT_MAX) {}
+ SectionIndex(INT_MAX) {
+ Live = false;
+}
-static uint64_t updateOffset(uint64_t Off, InputSection *S) {
- Off = alignTo(Off, S->Alignment);
- S->OutSecOff = Off;
- return Off + S->getSize();
+// We allow sections of types listed below to merged into a
+// single progbits section. This is typically done by linker
+// scripts. Merging nobits and progbits will force disk space
+// to be allocated for nobits sections. Other ones don't require
+// any special treatment on top of progbits, so there doesn't
+// seem to be a harm in merging them.
+static bool canMergeToProgbits(unsigned Type) {
+ return Type == SHT_NOBITS || Type == SHT_PROGBITS || Type == SHT_INIT_ARRAY ||
+ Type == SHT_PREINIT_ARRAY || Type == SHT_FINI_ARRAY ||
+ Type == SHT_NOTE;
}
-void OutputSection::addSection(InputSection *S) {
- assert(S->Live);
- Sections.push_back(S);
- S->Parent = this;
- this->updateAlignment(S->Alignment);
+void OutputSection::addSection(InputSection *IS) {
+ if (!Live) {
+ // If IS is the first section to be added to this section,
+ // initialize Type and Entsize from IS.
+ Live = true;
+ Type = IS->Type;
+ Entsize = IS->Entsize;
+ } else {
+ // Otherwise, check if new type or flags are compatible with existing ones.
+ if ((Flags & (SHF_ALLOC | SHF_TLS)) != (IS->Flags & (SHF_ALLOC | SHF_TLS)))
+ error("incompatible section flags for " + Name + "\n>>> " + toString(IS) +
+ ": 0x" + utohexstr(IS->Flags) + "\n>>> output section " + Name +
+ ": 0x" + utohexstr(Flags));
+
+ if (Type != IS->Type) {
+ if (!canMergeToProgbits(Type) || !canMergeToProgbits(IS->Type))
+ error("section type mismatch for " + IS->Name + "\n>>> " +
+ toString(IS) + ": " +
+ getELFSectionTypeName(Config->EMachine, IS->Type) +
+ "\n>>> output section " + Name + ": " +
+ getELFSectionTypeName(Config->EMachine, Type));
+ Type = SHT_PROGBITS;
+ }
+ }
- // The actual offsets will be computed by assignAddresses. For now, use
- // crude approximation so that it is at least easy for other code to know the
- // section order. It is also used to calculate the output section size early
- // for compressed debug sections.
- this->Size = updateOffset(Size, S);
+ IS->Parent = this;
+ Flags |= IS->Flags;
+ Alignment = std::max(Alignment, IS->Alignment);
+ IS->OutSecOff = Size++;
// If this section contains a table of fixed-size entries, sh_entsize
- // holds the element size. Consequently, if this contains two or more
- // input sections, all of them must have the same sh_entsize. However,
- // you can put different types of input sections into one output
- // sectin by using linker scripts. I don't know what to do here.
- // Probably we sholuld handle that as an error. But for now we just
- // pick the largest sh_entsize.
- this->Entsize = std::max(this->Entsize, S->Entsize);
+ // holds the element size. If it contains elements of different size we
+ // set sh_entsize to 0.
+ if (Entsize != IS->Entsize)
+ Entsize = 0;
+
+ if (!IS->Assigned) {
+ IS->Assigned = true;
+ if (SectionCommands.empty() ||
+ !isa<InputSectionDescription>(SectionCommands.back()))
+ SectionCommands.push_back(make<InputSectionDescription>(""));
+ auto *ISD = cast<InputSectionDescription>(SectionCommands.back());
+ ISD->Sections.push_back(IS);
+ }
}
-static SectionKey createKey(InputSectionBase *C, StringRef 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.
-
- uint32_t Alignment = 0;
- uint64_t Flags = 0;
- if (Config->Relocatable && (C->Flags & SHF_MERGE)) {
- Alignment = std::max<uint64_t>(C->Alignment, C->Entsize);
- Flags = C->Flags & (SHF_MERGE | SHF_STRINGS);
- }
+void elf::sortByOrder(MutableArrayRef<InputSection *> In,
+ std::function<int(InputSectionBase *S)> Order) {
+ typedef std::pair<int, InputSection *> Pair;
+ auto Comp = [](const Pair &A, const Pair &B) { return A.first < B.first; };
+
+ std::vector<Pair> V;
+ for (InputSection *S : In)
+ V.push_back({Order(S), S});
+ std::stable_sort(V.begin(), V.end(), Comp);
- return SectionKey{OutsecName, Flags, Alignment};
+ for (size_t I = 0; I < V.size(); ++I)
+ In[I] = V[I].second;
}
-OutputSectionFactory::OutputSectionFactory() {}
+uint64_t elf::getHeaderSize() {
+ if (Config->OFormatBinary)
+ return 0;
+ return Out::ElfHeader->Size + Out::ProgramHeaders->Size;
+}
-static uint64_t getIncompatibleFlags(uint64_t Flags) {
- return Flags & (SHF_ALLOC | SHF_TLS);
+bool OutputSection::classof(const BaseCommand *C) {
+ return C->Kind == OutputSectionKind;
}
-// We allow sections of types listed below to merged into a
-// single progbits section. This is typically done by linker
-// scripts. Merging nobits and progbits will force disk space
-// to be allocated for nobits sections. Other ones don't require
-// any special treatment on top of progbits, so there doesn't
-// seem to be a harm in merging them.
-static bool canMergeToProgbits(unsigned Type) {
- return Type == SHT_NOBITS || Type == SHT_PROGBITS || Type == SHT_INIT_ARRAY ||
- Type == SHT_PREINIT_ARRAY || Type == SHT_FINI_ARRAY ||
- Type == SHT_NOTE;
+void OutputSection::sort(std::function<int(InputSectionBase *S)> Order) {
+ assert(Live);
+ assert(SectionCommands.size() == 1);
+ sortByOrder(cast<InputSectionDescription>(SectionCommands[0])->Sections,
+ Order);
}
-void elf::reportDiscarded(InputSectionBase *IS) {
- if (!Config->PrintGcSections)
- return;
- message("removing unused section from '" + IS->Name + "' in file '" +
- IS->File->getName() + "'");
+// 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);
}
-void OutputSectionFactory::addInputSec(InputSectionBase *IS,
- StringRef OutsecName) {
- // Sections with the SHT_GROUP attribute reach here only when the - r option
- // is given. Such sections define "section groups", and InputFiles.cpp has
- // dedup'ed section groups by their signatures. For the -r, we want to pass
- // through all SHT_GROUP sections without merging them because merging them
- // creates broken section contents.
- if (IS->Type == SHT_GROUP) {
- OutputSection *Out = nullptr;
- addInputSec(IS, OutsecName, Out);
- return;
- }
+// Compress section contents if this section contains debug info.
+template <class ELFT> void OutputSection::maybeCompress() {
+ typedef typename ELFT::Chdr Elf_Chdr;
- // 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();
- addInputSec(IS, OutsecName, Out->RelocationSection);
+ // Compress only DWARF debug sections.
+ if (!Config->CompressDebugSections || (Flags & SHF_ALLOC) ||
+ !Name.startswith(".debug_"))
return;
- }
- SectionKey Key = createKey(IS, OutsecName);
- OutputSection *&Sec = Map[Key];
- addInputSec(IS, OutsecName, Sec);
+ // Calculate the section offsets and size pre-compression.
+ Size = 0;
+ for (BaseCommand *Cmd : SectionCommands)
+ if (auto *ISD = dyn_cast<InputSectionDescription>(Cmd))
+ for (InputSection *IS : ISD->Sections) {
+ IS->OutSecOff = alignTo(Size, IS->Alignment);
+ this->Size = IS->OutSecOff + IS->getSize();
+ }
+
+ // Create a section header.
+ ZDebugHeader.resize(sizeof(Elf_Chdr));
+ auto *Hdr = reinterpret_cast<Elf_Chdr *>(ZDebugHeader.data());
+ Hdr->ch_type = ELFCOMPRESS_ZLIB;
+ Hdr->ch_size = Size;
+ Hdr->ch_addralign = Alignment;
+
+ // Write section contents to a temporary buffer and compress it.
+ std::vector<uint8_t> Buf(Size);
+ writeTo<ELFT>(Buf.data());
+ if (Error E = zlib::compress(toStringRef(Buf), CompressedData))
+ fatal("compress failed: " + llvm::toString(std::move(E)));
+
+ // Update section headers.
+ Size = sizeof(Elf_Chdr) + CompressedData.size();
+ Flags |= SHF_COMPRESSED;
}
-void OutputSectionFactory::addInputSec(InputSectionBase *IS,
- StringRef OutsecName,
- OutputSection *&Sec) {
- if (!IS->Live) {
- reportDiscarded(IS);
+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");
+}
+
+template <class ELFT> void OutputSection::writeTo(uint8_t *Buf) {
+ if (Type == SHT_NOBITS)
+ return;
+
+ 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 (!CompressedData.empty()) {
+ memcpy(Buf, ZDebugHeader.data(), ZDebugHeader.size());
+ memcpy(Buf + ZDebugHeader.size(), CompressedData.data(),
+ CompressedData.size());
return;
}
- if (Sec) {
- if (getIncompatibleFlags(Sec->Flags) != getIncompatibleFlags(IS->Flags))
- error("incompatible section flags for " + Sec->Name + "\n>>> " +
- toString(IS) + ": 0x" + utohexstr(IS->Flags) +
- "\n>>> output section " + Sec->Name + ": 0x" +
- utohexstr(Sec->Flags));
- if (Sec->Type != IS->Type) {
- if (canMergeToProgbits(Sec->Type) && canMergeToProgbits(IS->Type))
- Sec->Type = SHT_PROGBITS;
+ // Write leading padding.
+ std::vector<InputSection *> Sections;
+ for (BaseCommand *Cmd : SectionCommands)
+ 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() ? 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 + Size;
else
- error("section type mismatch for " + IS->Name + "\n>>> " +
- toString(IS) + ": " +
- getELFSectionTypeName(Config->EMachine, IS->Type) +
- "\n>>> output section " + Sec->Name + ": " +
- getELFSectionTypeName(Config->EMachine, Sec->Type));
+ End = Buf + Sections[I + 1]->OutSecOff;
+ fill(Start, End - Start, Filler);
}
- Sec->Flags |= IS->Flags;
- } else {
- Sec = make<OutputSection>(OutsecName, IS->Type, IS->Flags);
- OutputSections.push_back(Sec);
+ });
+
+ // Linker scripts may have BYTE()-family commands with which you
+ // can write arbitrary bytes to the output. Process them if any.
+ for (BaseCommand *Base : SectionCommands)
+ if (auto *Data = dyn_cast<ByteCommand>(Base))
+ writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
+}
+
+template <class ELFT>
+static void finalizeShtGroup(OutputSection *OS,
+ InputSection *Section) {
+ assert(Config->Relocatable);
+
+ // 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.
+ ObjFile<ELFT> *Obj = Section->getFile<ELFT>();
+ ArrayRef<Symbol *> Symbols = Obj->getSymbols();
+ OS->Info = InX::SymTab->getSymbolIndex(Symbols[Section->Info]);
+}
+
+template <class ELFT> void OutputSection::finalize() {
+ InputSection *First = nullptr;
+ for (BaseCommand *Base : SectionCommands) {
+ if (auto *ISD = dyn_cast<InputSectionDescription>(Base)) {
+ if (ISD->Sections.empty())
+ continue;
+ if (First == nullptr)
+ First = ISD->Sections.front();
+ }
+ if (isa<ByteCommand>(Base) && Type == SHT_NOBITS)
+ Type = SHT_PROGBITS;
+ }
+
+ if (Flags & SHF_LINK_ORDER) {
+ // 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 = First->getLinkOrderDep())
+ Link = D->getParent()->SectionIndex;
+ }
+
+ if (Type == SHT_GROUP) {
+ finalizeShtGroup<ELFT>(this, First);
+ return;
}
- Sec->addSection(cast<InputSection>(IS));
+ if (!Config->CopyRelocs || (Type != SHT_RELA && Type != SHT_REL))
+ return;
+
+ if (isa<SyntheticSection>(First))
+ return;
+
+ 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();
+ Info = S->getOutputSection()->SectionIndex;
+ Flags |= SHF_INFO_LINK;
+}
+
+// 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);
}
-OutputSectionFactory::~OutputSectionFactory() {}
+static bool isCrtbegin(StringRef S) { return isCrtBeginEnd(S, "crtbegin"); }
+static bool isCrtend(StringRef S) { return isCrtBeginEnd(S, "crtend"); }
-SectionKey DenseMapInfo<SectionKey>::getEmptyKey() {
- return SectionKey{DenseMapInfo<StringRef>::getEmptyKey(), 0, 0};
+// .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".
+//
+// 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;
}
-SectionKey DenseMapInfo<SectionKey>::getTombstoneKey() {
- return SectionKey{DenseMapInfo<StringRef>::getTombstoneKey(), 0, 0};
+// 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 OutputSection::sortCtorsDtors() {
+ assert(SectionCommands.size() == 1);
+ auto *ISD = cast<InputSectionDescription>(SectionCommands[0]);
+ std::stable_sort(ISD->Sections.begin(), ISD->Sections.end(), compCtors);
}
-unsigned DenseMapInfo<SectionKey>::getHashValue(const SectionKey &Val) {
- return hash_combine(Val.Name, Val.Flags, Val.Alignment);
+// 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.
+int elf::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;
}
-bool DenseMapInfo<SectionKey>::isEqual(const SectionKey &LHS,
- const SectionKey &RHS) {
- return DenseMapInfo<StringRef>::isEqual(LHS.Name, RHS.Name) &&
- LHS.Flags == RHS.Flags && LHS.Alignment == RHS.Alignment;
+// 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 OutputSection::sortInitFini() {
+ // Sort sections by priority.
+ sort([](InputSectionBase *S) { return getPriority(S->Name); });
}
-uint64_t elf::getHeaderSize() {
- if (Config->OFormatBinary)
- return 0;
- return Out::ElfHeader->Size + Out::ProgramHeaders->Size;
+uint32_t OutputSection::getFiller() {
+ if (Filler)
+ return *Filler;
+ if (Flags & SHF_EXECINSTR)
+ return Target->TrapInstr;
+ return 0;
}
template void OutputSection::writeHeaderTo<ELF32LE>(ELF32LE::Shdr *Shdr);
template void OutputSection::writeHeaderTo<ELF32BE>(ELF32BE::Shdr *Shdr);
template void OutputSection::writeHeaderTo<ELF64LE>(ELF64LE::Shdr *Shdr);
template void OutputSection::writeHeaderTo<ELF64BE>(ELF64BE::Shdr *Shdr);
+
+template void OutputSection::writeTo<ELF32LE>(uint8_t *Buf);
+template void OutputSection::writeTo<ELF32BE>(uint8_t *Buf);
+template void OutputSection::writeTo<ELF64LE>(uint8_t *Buf);
+template void OutputSection::writeTo<ELF64BE>(uint8_t *Buf);
+
+template void OutputSection::maybeCompress<ELF32LE>();
+template void OutputSection::maybeCompress<ELF32BE>();
+template void OutputSection::maybeCompress<ELF64LE>();
+template void OutputSection::maybeCompress<ELF64BE>();
+
+template void OutputSection::finalize<ELF32LE>();
+template void OutputSection::finalize<ELF32BE>();
+template void OutputSection::finalize<ELF64LE>();
+template void OutputSection::finalize<ELF64BE>();
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