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ARM: Resolve thumb_bl fixup in same MCFragment.

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In Thumb1 mode, bl instruction might be selected for branches between
basic blocks in the function if the offset is greater than 2KB.
However, this might cause SEGV because the destination symbol
is not marked as thumb function and the execution mode will be reset
to ARM mode.

Since we are sure that these symbols are in the same data fragment, we
can simply resolve these local symbols, and don't emit any relocation
information for this bl instruction.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200842 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Logan Chien
2014-02-05 14:15:16 +00:00
parent 1ee5ca7005
commit 575c4addce
2 changed files with 34 additions and 1 deletions
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9
lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
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@@ -565,11 +565,18 @@ void ARMAsmBackend::processFixupValue(const MCAssembler &Asm,
Value |= 1;
}
}
// For Thumb1 BL instruction, it is possible to be a long jump between
// the basic blocks of the same function. Thus, we would like to resolve
// the offset when the destination has the same MCFragment.
if (A && (unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_bl) {
const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
MCSymbolData &SymData = Asm.getSymbolData(Sym);
IsResolved = (SymData.getFragment() == DF);
}
// We must always generate a relocation for BL/BLX instructions if we have
// a symbol to reference, as the linker relies on knowing the destination
// symbol's thumb-ness to get interworking right.
if (A && ((unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_blx ||
(unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_bl ||
(unsigned)Fixup.getKind() == ARM::fixup_arm_blx ||
(unsigned)Fixup.getKind() == ARM::fixup_arm_uncondbl ||
(unsigned)Fixup.getKind() == ARM::fixup_arm_condbl))