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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);
}
}
// Page(Expr) is the page address of the expression Expr, defined
// as (Expr & ~0xFFF). (This applies even if the machine page size
// supported by the platform has a different value.)
static uint64_t getAArch64Page(uint64_t Expr) {
return Expr & (~static_cast<uint64_t>(0xFFF));
}
template <class ELFT>
static typename ELFT::uint
getSymVA(uint32_t Type, typename ELFT::uint A, typename ELFT::uint P,
const SymbolBody &Body, uint8_t *BufLoc,
const elf::ObjectFile<ELFT> &File, RelExpr Expr) {
switch (Expr) {
case R_TLSLD:
return Out<ELFT>::Got->getTlsIndexVA() + A;
case R_TLSLD_PC:
return Out<ELFT>::Got->getTlsIndexVA() + A - P;
case R_THUNK:
return Body.getThunkVA<ELFT>();
case R_PPC_TOC:
return getPPC64TocBase() + A;
case R_TLSGD:
return Out<ELFT>::Got->getGlobalDynAddr(Body) + A;
case R_TLSGD_PC:
return Out<ELFT>::Got->getGlobalDynAddr(Body) + A - P;
case R_PLT:
return Body.getPltVA<ELFT>() + A;
case R_PLT_PC:
case R_PPC_PLT_OPD:
return Body.getPltVA<ELFT>() + A - P;
case R_SIZE:
return Body.getSize<ELFT>() + A;
case R_GOT:
case R_RELAX_TLS_GD_TO_IE:
return Body.getGotVA<ELFT>() + A;
case R_GOT_PAGE_PC:
return getAArch64Page(Body.getGotVA<ELFT>() + A) - getAArch64Page(P);
case R_GOT_PC:
case R_RELAX_TLS_GD_TO_IE_PC:
return Body.getGotVA<ELFT>() + A - P;
case R_ABS:
case R_RELAX_TLS_GD_TO_LE:
case R_RELAX_TLS_IE_TO_LE:
case R_RELAX_TLS_LD_TO_LE:
return Body.getVA<ELFT>(A);
case R_MIPS_GP0:
// 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 Body.getVA<ELFT>(A) + File.getMipsGp0();
case R_MIPS_GOT_LOCAL:
// 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(Body.getVA<ELFT>(A));
case R_MIPS_GOT:
// 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->getMipsLocalEntryAddr(Body.getVA<ELFT>(A));
case R_PPC_OPD: {
uint64_t SymVA = Body.getVA<ELFT>(A);
// If we have an undefined weak symbol, we might get here with a symbol
// address of zero. That could overflow, but the code must be unreachable,
// so don't bother doing anything at all.
if (!SymVA)
return 0;
if (Out<ELF64BE>::Opd) {
// If this is a local call, and we currently have the address of a
// function-descriptor, get the underlying code address instead.
uint64_t OpdStart = Out<ELF64BE>::Opd->getVA();
uint64_t OpdEnd = OpdStart + Out<ELF64BE>::Opd->getSize();
bool InOpd = OpdStart <= SymVA && SymVA < OpdEnd;
if (InOpd)
SymVA = read64be(&Out<ELF64BE>::OpdBuf[SymVA - OpdStart]);
}
return SymVA - P;
}
case R_PC:
return Body.getVA<ELFT>(A) - P;
case R_PAGE_PC:
return getAArch64Page(Body.getVA<ELFT>(A)) - getAArch64Page(P);
}
llvm_unreachable("Invalid expression");
}
template <class ELFT>
void InputSectionBase<ELFT>::relocate(uint8_t *Buf, uint8_t *BufEnd) {
const unsigned Bits = sizeof(uintX_t) * 8;
for (const Relocation &Rel : Relocations) {
uintX_t Offset = Rel.Offset;
uint8_t *BufLoc = Buf + Offset;
uint32_t Type = Rel.Type;
uintX_t A = Rel.Addend;
uintX_t AddrLoc = OutSec->getVA() + Offset;
RelExpr Expr = Rel.Expr;
uint64_t SymVA = SignExtend64<Bits>(
getSymVA<ELFT>(Type, A, AddrLoc, *Rel.Sym, BufLoc, *File, Expr));
if (Expr == R_RELAX_TLS_IE_TO_LE) {
Target->relaxTlsIeToLe(BufLoc, Type, SymVA);
continue;
}
if (Expr == R_RELAX_TLS_LD_TO_LE) {
Target->relaxTlsLdToLe(BufLoc, Type, SymVA);
continue;
}
if (Expr == R_RELAX_TLS_GD_TO_LE) {
Target->relaxTlsGdToLe(BufLoc, Type, SymVA);
continue;
}
if (Expr == R_RELAX_TLS_GD_TO_IE_PC || Expr == R_RELAX_TLS_GD_TO_IE) {
Target->relaxTlsGdToIe(BufLoc, Type, SymVA);
continue;
}
if (Expr == R_PPC_PLT_OPD) {
uint32_t Nop = 0x60000000;
if (BufLoc + 8 <= BufEnd && read32be(BufLoc + 4) == Nop)
write32be(BufLoc + 4, 0xe8410028); // ld %r2, 40(%r1)
}
Target->relocateOne(BufLoc, Type, 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();
this->relocate(Buf, BufEnd);
// 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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