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Add r224985 back with a fix.

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The issues was that AArch64 has additional restrictions on when local
relocations can be used. We have to take those into consideration when
deciding to put a L symbol in the symbol table or not.

Original message:

Remove doesSectionRequireSymbols.

In an assembly expression like

bar:
.long L0 + 1

the intended semantics is that bar will contain a pointer one byte past L0.

In sections that are merged by content (strings, 4 byte constants, etc), a
single position in the section doesn't give the linker enough information.
For example, it would not be able to tell a relocation must point to the
end of a string, since that would look just like the start of the next.

The solution used in ELF to use relocation with symbols if there is a non-zero
addend.

In MachO before this patch we would just keep all symbols in some sections.

This would miss some cases (only cstrings on x86_64 were implemented) and was
inefficient since most relocations have an addend of 0 and can be represented
without the symbol.

This patch implements the non-zero addend logic for MachO too.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225048 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola
2014-12-31 17:19:34 +00:00
parent f5943bd9a9
commit 8093abb745
19 changed files with 302 additions and 246 deletions
Download Patch File Download Diff File Expand all files Collapse all files

41
lib/MC/MachObjectWriter.cpp
View File

@ -448,14 +448,11 @@ void MachObjectWriter::WriteLinkerOptionsLoadCommand(
assert(OS.tell() - Start == Size);
}
void MachObjectWriter::RecordRelocation(const MCAssembler &Asm,
void MachObjectWriter::RecordRelocation(MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
bool &IsPCRel,
uint64_t &FixedValue) {
const MCFixup &Fixup, MCValue Target,
bool &IsPCRel, uint64_t &FixedValue) {
TargetObjectWriter->RecordRelocation(this, Asm, Layout, Fragment, Fixup,
Target, FixedValue);
}
@ -616,6 +613,22 @@ void MachObjectWriter::ComputeSymbolTable(
ExternalSymbolData[i].SymbolData->setIndex(Index++);
for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
UndefinedSymbolData[i].SymbolData->setIndex(Index++);
for (const MCSectionData &SD : Asm) {
std::vector<RelAndSymbol> &Relocs = Relocations[&SD];
for (RelAndSymbol &Rel : Relocs) {
if (!Rel.Sym)
continue;
// Set the Index and the IsExtern bit.
unsigned Index = Rel.Sym->getIndex();
assert(isInt<24>(Index));
if (IsLittleEndian)
Rel.MRE.r_word1 = (Rel.MRE.r_word1 & (-1 << 24)) | Index | (1 << 27);
else
Rel.MRE.r_word1 = (Rel.MRE.r_word1 & 0xff) | Index << 8 | (1 << 4);
}
}
}
void MachObjectWriter::computeSectionAddresses(const MCAssembler &Asm,
@ -662,10 +675,6 @@ void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
// Mark symbol difference expressions in variables (from .set or = directives)
// as absolute.
markAbsoluteVariableSymbols(Asm, Layout);
// Compute symbol table information and bind symbol indices.
ComputeSymbolTable(Asm, LocalSymbolData, ExternalSymbolData,
UndefinedSymbolData);
}
bool MachObjectWriter::
@ -749,6 +758,10 @@ IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
void MachObjectWriter::WriteObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
// Compute symbol table information and bind symbol indices.
ComputeSymbolTable(Asm, LocalSymbolData, ExternalSymbolData,
UndefinedSymbolData);
unsigned NumSections = Asm.size();
const MCAssembler::VersionMinInfoType &VersionInfo =
Layout.getAssembler().getVersionMinInfo();
@ -839,7 +852,7 @@ void MachObjectWriter::WriteObject(MCAssembler &Asm,
uint64_t RelocTableEnd = SectionDataStart + SectionDataFileSize;
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
std::vector<MachO::any_relocation_info> &Relocs = Relocations[it];
std::vector<RelAndSymbol> &Relocs = Relocations[it];
unsigned NumRelocs = Relocs.size();
uint64_t SectionStart = SectionDataStart + getSectionAddress(it);
WriteSection(Asm, Layout, *it, SectionStart, RelocTableEnd, NumRelocs);
@ -933,10 +946,10 @@ void MachObjectWriter::WriteObject(MCAssembler &Asm,
ie = Asm.end(); it != ie; ++it) {
// Write the section relocation entries, in reverse order to match 'as'
// (approximately, the exact algorithm is more complicated than this).
std::vector<MachO::any_relocation_info> &Relocs = Relocations[it];
std::vector<RelAndSymbol> &Relocs = Relocations[it];
for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
Write32(Relocs[e - i - 1].r_word0);
Write32(Relocs[e - i - 1].r_word1);
Write32(Relocs[e - i - 1].MRE.r_word0);
Write32(Relocs[e - i - 1].MRE.r_word1);
}
}