[llvm] r233119 - AArch64: use a different means to determine whether to byte swap relocations.

[Rafael Espíndola]

This is testable. The new code should be able to handle more situations.

On 24 March 2015 at 17:47, Peter Collingbourne <peter at pcc.me.uk> wrote:
> Author: pcc
> Date: Tue Mar 24 16:47:03 2015
> New Revision: 233119
>
> URL: http://llvm.org/viewvc/llvm-project?rev=233119&view=rev
> Log:
> AArch64: use a different means to determine whether to byte swap relocations.
>
> This code depended on a bug in the FindAssociatedSection function that would
> cause it to return the wrong result for certain absolute expressions. Instead,
> use EvaluateAsRelocatable.
>
> Modified:
>     llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
>
> Modified: llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp?rev=233119&r1=233118&r2=233119&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp (original)
> +++ llvm/trunk/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp Tue Mar 24 16:47:03 2015
> @@ -18,6 +18,7 @@
>  #include "llvm/MC/MCObjectWriter.h"
>  #include "llvm/MC/MCSectionELF.h"
>  #include "llvm/MC/MCSectionMachO.h"
> +#include "llvm/MC/MCValue.h"
>  #include "llvm/Support/ErrorHandling.h"
>  #include "llvm/Support/MachO.h"
>  using namespace llvm;
> @@ -493,14 +494,28 @@ void ELFAArch64AsmBackend::processFixupV
>      IsResolved = false;
>  }
>
> +// Returns whether this fixup is based on an address in the .eh_frame section,
> +// and therefore should be byte swapped.
> +// FIXME: Should be replaced with something more principled.
> +static bool isByteSwappedFixup(const MCExpr *E) {
> +  MCValue Val;
> +  if (!E->EvaluateAsRelocatable(Val, nullptr, nullptr))
> +    return false;
> +
> +  if (!Val.getSymA() || Val.getSymA()->getSymbol().isUndefined())
> +    return false;
> +
> +  const MCSectionELF *SecELF =
> +      dyn_cast<MCSectionELF>(&Val.getSymA()->getSymbol().getSection());
> +  return SecELF->getSectionName() == ".eh_frame";
> +}
> +
>  void ELFAArch64AsmBackend::applyFixup(const MCFixup &Fixup, char *Data,
>                                        unsigned DataSize, uint64_t Value,
>                                        bool IsPCRel) const {
>    // store fixups in .eh_frame section in big endian order
>    if (!IsLittleEndian && Fixup.getKind() == FK_Data_4) {
> -    const MCSection *Sec = Fixup.getValue()->FindAssociatedSection();
> -    const MCSectionELF *SecELF = dyn_cast_or_null<const MCSectionELF>(Sec);
> -    if (SecELF && SecELF->getSectionName() == ".eh_frame")
> +    if (isByteSwappedFixup(Fixup.getValue()))
>        Value = ByteSwap_32(unsigned(Value));
>    }
>    AArch64AsmBackend::applyFixup (Fixup, Data, DataSize, Value, IsPCRel);
>
>
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