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22ef956a45e01463f24e7b7d335606f301865b3f
llvm/lld/ELF/InputSection.cpp
Rafael Espindola 22ef956a45 Change how we apply relocations. 
With this patch we use the first scan over the relocations to remember
the information we found about them: will them be relaxed, will a plt be
used, etc.

With that the actual relocation application becomes much simpler. That
is particularly true for the interfaces in Target.h.

This unfortunately means that we now do two passes over relocations for
non SHF_ALLOC sections. I think this can be solved by factoring out the
code that scans a single relocation. It can then be used both as a scan
that record info and for a dedicated direct relocation of non SHF_ALLOC
sections.

I also think it is possible to reduce the number of enum values by
representing a target with just an OutputSection and an offset (which
can be from the start or end).

This should unblock adding features like relocation optimizations.

llvm-svn: 266158
2016-04-13 01:40:19 +00:00

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16 KiB
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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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