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

[Rafael Espíndola]

Oh, and the code should be checking SymB too.

A logic similar to getBaseSymbol is probably what is needed.

On 24 March 2015 at 18:03, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
> 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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