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Add r224985 back with fixes.

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The fixes are to note that AArch64 has additional restrictions on when local
relocations can be used. In particular, ld64 requires that relocations to
cstring/cfstrings use linker visible symbols.

Original message:

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@226503 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola
2015-01-19 21:11:14 +00:00
parent a7852bfa47
commit a23cc6a1ea
19 changed files with 323 additions and 246 deletions
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16
lib/MC/MCAssembler.cpp
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@@ -435,6 +435,16 @@ bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
return true;
}
void MCAssembler::addLocalUsedInReloc(const MCSymbol &Sym) {
assert(Sym.isTemporary());
LocalsUsedInReloc.insert(&Sym);
}
bool MCAssembler::isLocalUsedInReloc(const MCSymbol &Sym) const {
assert(Sym.isTemporary());
return LocalsUsedInReloc.count(&Sym);
}
bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
// Non-temporary labels should always be visible to the linker.
if (!Symbol.isTemporary())
@@ -444,8 +454,10 @@ bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
if (!Symbol.isInSection())
return false;
// Otherwise, check if the section requires symbols even for temporary labels.
return getBackend().doesSectionRequireSymbols(Symbol.getSection());
if (isLocalUsedInReloc(Symbol))
return true;
return false;
}
const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {