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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

28
include/llvm/MC/MCMachObjectWriter.h
View File

@ -68,12 +68,10 @@ public:
/// @name API
/// @{
virtual void RecordRelocation(MachObjectWriter *Writer,
const MCAssembler &Asm,
virtual void RecordRelocation(MachObjectWriter *Writer, MCAssembler &Asm,
const MCAsmLayout &Layout,
const MCFragment *Fragment,
const MCFixup &Fixup,
MCValue Target,
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue) = 0;
/// @}
@ -97,8 +95,14 @@ class MachObjectWriter : public MCObjectWriter {
/// @name Relocation Data
/// @{
llvm::DenseMap<const MCSectionData*,
std::vector<MachO::any_relocation_info> > Relocations;
struct RelAndSymbol {
const MCSymbolData *Sym;
MachO::any_relocation_info MRE;
RelAndSymbol(const MCSymbolData *Sym, const MachO::any_relocation_info &MRE)
: Sym(Sym), MRE(MRE) {}
};
llvm::DenseMap<const MCSectionData *, std::vector<RelAndSymbol>> Relocations;
llvm::DenseMap<const MCSectionData*, unsigned> IndirectSymBase;
/// @}
@ -213,9 +217,15 @@ public:
// - Input errors, where something cannot be correctly encoded. 'as' allows
// these through in many cases.
void addRelocation(const MCSectionData *SD,
// Add a relocation to be output in the object file. At the time this is
// called, the symbol indexes are not know, so if the relocation refers
// to a symbol it should be passed as \p RelSymbol so that it can be updated
// afterwards. If the relocation doesn't refer to a symbol, nullptr should be
// used.
void addRelocation(const MCSymbolData *RelSymbol, const MCSectionData *SD,
MachO::any_relocation_info &MRE) {
Relocations[SD].push_back(MRE);
RelAndSymbol P(RelSymbol, MRE);
Relocations[SD].push_back(P);
}
void RecordScatteredRelocation(const MCAssembler &Asm,
@ -231,7 +241,7 @@ public:
const MCFixup &Fixup, MCValue Target,
uint64_t &FixedValue);
void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
const MCFragment *Fragment, const MCFixup &Fixup,
MCValue Target, bool &IsPCRel,
uint64_t &FixedValue) override;