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hanchenye-llvm-project/lld/ELF/InputSection.cpp

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//===- InputSection.cpp ---------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "InputSection.h"
#include "Config.h"
#include "Error.h"
#include "InputFiles.h"
#include "OutputSections.h"
#include "Target.h"
#include "llvm/Support/Endian.h"
using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
template <class ELFT>
InputSectionBase<ELFT>::InputSectionBase(elf::ObjectFile<ELFT> *File,
const Elf_Shdr *Header,
Kind SectionKind)
: Header(Header), File(File), SectionKind(SectionKind), Repl(this) {
// The garbage collector sets sections' Live bits.
// If GC is disabled, all sections are considered live by default.
Live = !Config->GcSections;
// The ELF spec states that a value of 0 means the section has
// no alignment constraits.
Align = std::max<uintX_t>(Header->sh_addralign, 1);
}
template <class ELFT> size_t InputSectionBase<ELFT>::getSize() const {
if (auto *D = dyn_cast<InputSection<ELFT>>(this))
if (D->getThunksSize() > 0)
return D->getThunkOff() + D->getThunksSize();
return Header->sh_size;
}
template <class ELFT> StringRef InputSectionBase<ELFT>::getSectionName() const {
return check(File->getObj().getSectionName(this->Header));
}
template <class ELFT>
ArrayRef<uint8_t> InputSectionBase<ELFT>::getSectionData() const {
return check(this->File->getObj().getSectionContents(this->Header));
}
template <class ELFT>
typename ELFT::uint InputSectionBase<ELFT>::getOffset(uintX_t Offset) {
switch (SectionKind) {
case Regular:
return cast<InputSection<ELFT>>(this)->OutSecOff + Offset;
case EHFrame:
return cast<EHInputSection<ELFT>>(this)->getOffset(Offset);
case Merge:
return cast<MergeInputSection<ELFT>>(this)->getOffset(Offset);
case MipsReginfo:
// MIPS .reginfo sections are consumed by the linker,
// so it should never be copied to output.
llvm_unreachable("MIPS .reginfo reached writeTo().");
}
llvm_unreachable("invalid section kind");
}
template <class ELFT>
typename ELFT::uint
InputSectionBase<ELFT>::getOffset(const DefinedRegular<ELFT> &Sym) {
return getOffset(Sym.Value);
}
// Returns a section that Rel relocation is pointing to.
template <class ELFT>
InputSectionBase<ELFT> *
InputSectionBase<ELFT>::getRelocTarget(const Elf_Rel &Rel) const {
// Global symbol
uint32_t SymIndex = Rel.getSymbol(Config->Mips64EL);
SymbolBody &B = File->getSymbolBody(SymIndex).repl();
if (auto *D = dyn_cast<DefinedRegular<ELFT>>(&B))
if (D->Section)
return D->Section->Repl;
return nullptr;
}
template <class ELFT>
InputSectionBase<ELFT> *
InputSectionBase<ELFT>::getRelocTarget(const Elf_Rela &Rel) const {
return getRelocTarget(reinterpret_cast<const Elf_Rel &>(Rel));
}
template <class ELFT>
InputSection<ELFT>::InputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Header)
: InputSectionBase<ELFT>(F, Header, Base::Regular) {}
template <class ELFT>
bool InputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
return S->SectionKind == Base::Regular;
}
template <class ELFT>
InputSectionBase<ELFT> *InputSection<ELFT>::getRelocatedSection() {
assert(this->Header->sh_type == SHT_RELA || this->Header->sh_type == SHT_REL);
ArrayRef<InputSectionBase<ELFT> *> Sections = this->File->getSections();
return Sections[this->Header->sh_info];
}
template <class ELFT> void InputSection<ELFT>::addThunk(SymbolBody &Body) {
Body.ThunkIndex = Thunks.size();
Thunks.push_back(&Body);
}
template <class ELFT> uint64_t InputSection<ELFT>::getThunkOff() const {
return this->Header->sh_size;
}
template <class ELFT> uint64_t InputSection<ELFT>::getThunksSize() const {
return Thunks.size() * Target->ThunkSize;
}
// This is used for -r. We can't use memcpy to copy relocations because we need
// to update symbol table offset and section index for each relocation. So we
// copy relocations one by one.
template <class ELFT>
template <class RelTy>
void InputSection<ELFT>::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) {
InputSectionBase<ELFT> *RelocatedSection = getRelocatedSection();
for (const RelTy &Rel : Rels) {
uint32_t SymIndex = Rel.getSymbol(Config->Mips64EL);
uint32_t Type = Rel.getType(Config->Mips64EL);
SymbolBody &Body = this->File->getSymbolBody(SymIndex).repl();
RelTy *P = reinterpret_cast<RelTy *>(Buf);
Buf += sizeof(RelTy);
P->r_offset = RelocatedSection->getOffset(Rel.r_offset);
P->setSymbolAndType(Body.DynsymIndex, Type, Config->Mips64EL);
}
}
template <class RelTy>
static uint32_t getMipsPairType(const RelTy *Rel, const SymbolBody &Sym) {
switch (Rel->getType(Config->Mips64EL)) {
case R_MIPS_HI16:
return R_MIPS_LO16;
case R_MIPS_GOT16:
return Sym.isLocal() ? R_MIPS_LO16 : R_MIPS_NONE;
case R_MIPS_PCHI16:
return R_MIPS_PCLO16;
case R_MICROMIPS_HI16:
return R_MICROMIPS_LO16;
default:
return R_MIPS_NONE;
}
}
template <endianness E> static int16_t readSignedLo16(uint8_t *Loc) {
return read32<E>(Loc) & 0xffff;
}
template <class ELFT>
template <class RelTy>
int32_t
InputSectionBase<ELFT>::findMipsPairedAddend(uint8_t *Buf, uint8_t *BufLoc,
SymbolBody &Sym, const RelTy *Rel,
const RelTy *End) {
uint32_t SymIndex = Rel->getSymbol(Config->Mips64EL);
uint32_t Type = getMipsPairType(Rel, Sym);
// Some MIPS relocations use addend calculated from addend of the relocation
// itself and addend of paired relocation. ABI requires to compute such
// combined addend in case of REL relocation record format only.
// See p. 4-17 at ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
if (RelTy::IsRela || Type == R_MIPS_NONE)
return 0;
for (const RelTy *RI = Rel; RI != End; ++RI) {
if (RI->getType(Config->Mips64EL) != Type)
continue;
if (RI->getSymbol(Config->Mips64EL) != SymIndex)
continue;
uintX_t Offset = getOffset(RI->r_offset);
if (Offset == (uintX_t)-1)
break;
const endianness E = ELFT::TargetEndianness;
return ((read32<E>(BufLoc) & 0xffff) << 16) +
readSignedLo16<E>(Buf + Offset);
}
unsigned OldType = Rel->getType(Config->Mips64EL);
StringRef OldName = getELFRelocationTypeName(Config->EMachine, OldType);
StringRef NewName = getELFRelocationTypeName(Config->EMachine, Type);
warning("can't find matching " + NewName + " relocation for " + OldName);
return 0;
}
template <class ELFT, class uintX_t>
static uintX_t adjustMipsSymVA(uint32_t Type, const elf::ObjectFile<ELFT> &File,
const SymbolBody &Body, uintX_t AddrLoc,
uintX_t SymVA) {
if (Type == R_MIPS_HI16 && &Body == Config->MipsGpDisp)
return getMipsGpAddr<ELFT>() - AddrLoc;
if (Type == R_MIPS_LO16 && &Body == Config->MipsGpDisp)
return getMipsGpAddr<ELFT>() - AddrLoc + 4;
if (&Body == Config->MipsLocalGp)
return getMipsGpAddr<ELFT>();
if (Body.isLocal() && (Type == R_MIPS_GPREL16 || Type == R_MIPS_GPREL32))
// We need to adjust SymVA value in case of R_MIPS_GPREL16/32
// relocations because they use the following expression to calculate
// the relocation's result for local symbol: S + A + GP0 - G.
return SymVA + File.getMipsGp0();
return SymVA;
}
template <class ELFT, class uintX_t>
static uintX_t getMipsGotVA(const SymbolBody &Body, uintX_t SymVA,
uint8_t *BufLoc) {
if (Body.isLocal())
// If relocation against MIPS local symbol requires GOT entry, this entry
// should be initialized by 'page address'. This address is high 16-bits
// of sum the symbol's value and the addend.
return Out<ELFT>::Got->getMipsLocalPageAddr(SymVA);
if (!Body.isPreemptible())
// For non-local symbols GOT entries should contain their full
// addresses. But if such symbol cannot be preempted, we do not
// have to put them into the "global" part of GOT and use dynamic
// linker to determine their actual addresses. That is why we
// create GOT entries for them in the "local" part of GOT.
return Out<ELFT>::Got->getMipsLocalFullAddr(Body);
return Body.getGotVA<ELFT>();
}
template <class ELFT>
template <class RelTy>
void InputSectionBase<ELFT>::relocate(uint8_t *Buf, uint8_t *BufEnd,
ArrayRef<RelTy> Rels) {
size_t Num = Rels.end() - Rels.begin();
for (size_t I = 0; I < Num; ++I) {
const RelTy &RI = *(Rels.begin() + I);
uintX_t Offset = getOffset(RI.r_offset);
if (Offset == (uintX_t)-1)
continue;
uintX_t A = getAddend<ELFT>(RI);
uint32_t SymIndex = RI.getSymbol(Config->Mips64EL);
uint32_t Type = RI.getType(Config->Mips64EL);
uint8_t *BufLoc = Buf + Offset;
uintX_t AddrLoc = OutSec->getVA() + Offset;
if (Target->pointsToLocalDynamicGotEntry(Type) &&
!Target->canRelaxTls(Type, nullptr)) {
Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc,
Out<ELFT>::Got->getTlsIndexVA() + A);
continue;
}
SymbolBody &Body = File->getSymbolBody(SymIndex).repl();
if (Target->canRelaxTls(Type, &Body)) {
uintX_t SymVA;
if (Target->needsGot(Type, Body))
SymVA = Body.getGotVA<ELFT>();
else
SymVA = Body.getVA<ELFT>();
// By optimizing TLS relocations, it is sometimes needed to skip
// relocations that immediately follow TLS relocations. This function
// knows how many slots we need to skip.
I += Target->relaxTls(BufLoc, BufEnd, Type, AddrLoc, SymVA, Body);
continue;
}
// PPC64 has a special relocation representing the TOC base pointer
// that does not have a corresponding symbol.
if (Config->EMachine == EM_PPC64 && RI.getType(false) == R_PPC64_TOC) {
uintX_t SymVA = getPPC64TocBase() + A;
Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc, SymVA);
continue;
}
if (Target->isTlsGlobalDynamicRel(Type) &&
!Target->canRelaxTls(Type, &Body)) {
Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc,
Out<ELFT>::Got->getGlobalDynAddr(Body) + A);
continue;
}
if (!RelTy::IsRela)
A += Target->getImplicitAddend(BufLoc, Type);
if (Config->EMachine == EM_MIPS)
A += findMipsPairedAddend(Buf, BufLoc, Body, &RI, Rels.end());
uintX_t SymVA = Body.getVA<ELFT>(A);
if (Target->needsPlt(Type, Body)) {
SymVA = Body.getPltVA<ELFT>() + A;
} else if (Target->needsGot(Type, Body)) {
if (Config->EMachine == EM_MIPS)
SymVA = getMipsGotVA<ELFT>(Body, SymVA, BufLoc);
else
SymVA = Body.getGotVA<ELFT>() + A;
if (Body.isTls())
Type = Target->getTlsGotRel(Type);
} else if (Target->isSizeRel(Type) && Body.isPreemptible()) {
// A SIZE relocation is supposed to set a symbol size, but if a symbol
// can be preempted, the size at runtime may be different than link time.
// If that's the case, we leave the field alone rather than filling it
// with a possibly incorrect value.
continue;
} else if (Target->needsThunk(Type, *this->getFile(), Body)) {
// Get address of a thunk code related to the symbol.
SymVA = Body.getThunkVA<ELFT>();
} else if (!Target->needsCopyRel<ELFT>(Type, Body) &&
Body.isPreemptible()) {
continue;
} else if (Config->EMachine == EM_MIPS) {
SymVA = adjustMipsSymVA<ELFT>(Type, *File, Body, AddrLoc, SymVA);
}
if (Target->isSizeRel(Type))
SymVA = Body.getSize<ELFT>() + A;
Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc, SymVA);
}
}
template <class ELFT> void InputSection<ELFT>::writeTo(uint8_t *Buf) {
if (this->Header->sh_type == SHT_NOBITS)
return;
ELFFile<ELFT> &EObj = this->File->getObj();
// If -r is given, then an InputSection may be a relocation section.
if (this->Header->sh_type == SHT_RELA) {
copyRelocations(Buf + OutSecOff, EObj.relas(this->Header));
return;
}
if (this->Header->sh_type == SHT_REL) {
copyRelocations(Buf + OutSecOff, EObj.rels(this->Header));
return;
}
// Copy section contents from source object file to output file.
ArrayRef<uint8_t> Data = this->getSectionData();
memcpy(Buf + OutSecOff, Data.data(), Data.size());
// Iterate over all relocation sections that apply to this section.
uint8_t *BufEnd = Buf + OutSecOff + Data.size();
for (const Elf_Shdr *RelSec : this->RelocSections) {
if (RelSec->sh_type == SHT_RELA)
this->relocate(Buf, BufEnd, EObj.relas(RelSec));
else
this->relocate(Buf, BufEnd, EObj.rels(RelSec));
}
// The section might have a data/code generated by the linker and need
// to be written after the section. Usually these are thunks - small piece
// of code used to jump between "incompatible" functions like PIC and non-PIC
// or if the jump target too far and its address does not fit to the short
// jump istruction.
if (!Thunks.empty()) {
Buf += OutSecOff + getThunkOff();
for (const SymbolBody *S : Thunks) {
Target->writeThunk(Buf, S->getVA<ELFT>());
Buf += Target->ThunkSize;
}
}
}
template <class ELFT>
void InputSection<ELFT>::replace(InputSection<ELFT> *Other) {
this->Align = std::max(this->Align, Other->Align);
Other->Repl = this->Repl;
Other->Live = false;
}
template <class ELFT>
SplitInputSection<ELFT>::SplitInputSection(
elf::ObjectFile<ELFT> *File, const Elf_Shdr *Header,
typename InputSectionBase<ELFT>::Kind SectionKind)
: InputSectionBase<ELFT>(File, Header, SectionKind) {}
template <class ELFT>
EHInputSection<ELFT>::EHInputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Header)
: SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::EHFrame) {
// Mark .eh_frame sections as live by default because there are
// usually no relocations that point to .eh_frames. Otherwise,
// the garbage collector would drop all .eh_frame sections.
this->Live = true;
}
template <class ELFT>
bool EHInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
return S->SectionKind == InputSectionBase<ELFT>::EHFrame;
}
template <class ELFT>
typename ELFT::uint EHInputSection<ELFT>::getOffset(uintX_t Offset) {
// The file crtbeginT.o has relocations pointing to the start of an empty
// .eh_frame that is known to be the first in the link. It does that to
// identify the start of the output .eh_frame. Handle this special case.
if (this->getSectionHdr()->sh_size == 0)
return Offset;
std::pair<uintX_t, uintX_t> *I = this->getRangeAndSize(Offset).first;
uintX_t Base = I->second;
if (Base == uintX_t(-1))
return -1; // Not in the output
uintX_t Addend = Offset - I->first;
return Base + Addend;
}
template <class ELFT>
MergeInputSection<ELFT>::MergeInputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Header)
: SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::Merge) {}
template <class ELFT>
bool MergeInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
return S->SectionKind == InputSectionBase<ELFT>::Merge;
}
template <class ELFT>
std::pair<std::pair<typename ELFT::uint, typename ELFT::uint> *,
typename ELFT::uint>
SplitInputSection<ELFT>::getRangeAndSize(uintX_t Offset) {
ArrayRef<uint8_t> D = this->getSectionData();
StringRef Data((const char *)D.data(), D.size());
uintX_t Size = Data.size();
if (Offset >= Size)
fatal("entry is past the end of the section");
// Find the element this offset points to.
auto I = std::upper_bound(
Offsets.begin(), Offsets.end(), Offset,
[](const uintX_t &A, const std::pair<uintX_t, uintX_t> &B) {
return A < B.first;
});
uintX_t End = I == Offsets.end() ? Data.size() : I->first;
--I;
return std::make_pair(&*I, End);
}
template <class ELFT>
typename ELFT::uint MergeInputSection<ELFT>::getOffset(uintX_t Offset) {
std::pair<std::pair<uintX_t, uintX_t> *, uintX_t> T =
this->getRangeAndSize(Offset);
std::pair<uintX_t, uintX_t> *I = T.first;
uintX_t End = T.second;
uintX_t Start = I->first;
// Compute the Addend and if the Base is cached, return.
uintX_t Addend = Offset - Start;
uintX_t &Base = I->second;
if (Base != uintX_t(-1))
return Base + Addend;
// Map the base to the offset in the output section and cache it.
ArrayRef<uint8_t> D = this->getSectionData();
StringRef Data((const char *)D.data(), D.size());
StringRef Entry = Data.substr(Start, End - Start);
Base =
static_cast<MergeOutputSection<ELFT> *>(this->OutSec)->getOffset(Entry);
return Base + Addend;
}
template <class ELFT>
MipsReginfoInputSection<ELFT>::MipsReginfoInputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Hdr)
: InputSectionBase<ELFT>(F, Hdr, InputSectionBase<ELFT>::MipsReginfo) {
// Initialize this->Reginfo.
ArrayRef<uint8_t> D = this->getSectionData();
if (D.size() != sizeof(Elf_Mips_RegInfo<ELFT>))
fatal("invalid size of .reginfo section");
Reginfo = reinterpret_cast<const Elf_Mips_RegInfo<ELFT> *>(D.data());
}
template <class ELFT>
bool MipsReginfoInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
return S->SectionKind == InputSectionBase<ELFT>::MipsReginfo;
}
template class elf::InputSectionBase<ELF32LE>;
template class elf::InputSectionBase<ELF32BE>;
template class elf::InputSectionBase<ELF64LE>;
template class elf::InputSectionBase<ELF64BE>;
template class elf::InputSection<ELF32LE>;
template class elf::InputSection<ELF32BE>;
template class elf::InputSection<ELF64LE>;
template class elf::InputSection<ELF64BE>;
template class elf::EHInputSection<ELF32LE>;
template class elf::EHInputSection<ELF32BE>;
template class elf::EHInputSection<ELF64LE>;
template class elf::EHInputSection<ELF64BE>;
template class elf::MergeInputSection<ELF32LE>;
template class elf::MergeInputSection<ELF32BE>;
template class elf::MergeInputSection<ELF64LE>;
template class elf::MergeInputSection<ELF64BE>;
template class elf::MipsReginfoInputSection<ELF32LE>;
template class elf::MipsReginfoInputSection<ELF32BE>;
template class elf::MipsReginfoInputSection<ELF64LE>;
template class elf::MipsReginfoInputSection<ELF64BE>;
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