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MC/Mach-O: Add isScatteredFixupFullyResolved, which implements the correct algorithm (used on x86_64) for determining whether an evaluated fixup is fully resolved (doesn't need relocation).

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- Test cases will follow, once we have x86_64 relocation support.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@98926 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Daniel Dunbar 2010-03-19 03:18:18 +00:00
parent 8ad0dccbf2
commit 034843ac8b
1 changed files with 59 additions and 1 deletions
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60
lib/MC/MCAssembler.cpp
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@ -1048,6 +1048,52 @@ static bool isScatteredFixupFullyResolvedSimple(const MCAssembler &Asm,
return true;
}
static bool isScatteredFixupFullyResolved(const MCAssembler &Asm,
const MCAsmFixup &Fixup,
const MCDataFragment *DF,
const MCValue Target,
const MCSymbolData *BaseSymbol) {
// The effective fixup address is
// addr(atom(A)) + offset(A)
// - addr(atom(B)) - offset(B)
// - addr(BaseSymbol) + <fixup offset from base symbol>
// and the offsets are not relocatable, so the fixup is fully resolved when
// addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0.
//
// Note that "false" is almost always conservatively correct (it means we emit
// a relocation which is unnecessary), except when it would force us to emit a
// relocation which the target cannot encode.
const MCSymbolData *A_Base = 0, *B_Base = 0;
if (const MCSymbolRefExpr *A = Target.getSymA()) {
// Modified symbol references cannot be resolved.
if (A->getKind() != MCSymbolRefExpr::VK_None)
return false;
A_Base = Asm.getAtom(&Asm.getSymbolData(A->getSymbol()));
if (!A_Base)
return false;
}
if (const MCSymbolRefExpr *B = Target.getSymB()) {
// Modified symbol references cannot be resolved.
if (B->getKind() != MCSymbolRefExpr::VK_None)
return false;
B_Base = Asm.getAtom(&Asm.getSymbolData(B->getSymbol()));
if (!B_Base)
return false;
}
// If there is no base, A and B have to be the same atom for this fixup to be
// fully resolved.
if (!BaseSymbol)
return A_Base == B_Base;
// Otherwise, B must be missing and A must be the base.
return !B_Base && BaseSymbol == A_Base;
}
bool MCAssembler::isSymbolLinkerVisible(const MCSymbolData *SD) const {
// Non-temporary labels should always be visible to the linker.
if (!SD->getSymbol().isTemporary())
@ -1128,7 +1174,19 @@ bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout, MCAsmFixup &Fixup,
// resolved; scattering may cause atoms to move.
if (IsResolved && getBackend().hasScatteredSymbols()) {
if (getBackend().hasReliableSymbolDifference()) {
llvm_report_error("FIXME: Not yet implemented");
// If this is a PCrel relocation, find the base atom (identified by its
// symbol) that the fixup value is relative to.
const MCSymbolData *BaseSymbol = 0;
if (IsPCRel) {
BaseSymbol = getAtomForAddress(
DF->getParent(), DF->getAddress() + Fixup.Offset);
if (!BaseSymbol)
IsResolved = false;
}
if (IsResolved)
IsResolved = isScatteredFixupFullyResolved(*this, Fixup, DF, Target,
BaseSymbol);
} else {
const MCSection *BaseSection = 0;
if (IsPCRel)