[cfe-dev] [LLVMdev] fatal error: error in backend: 32-bit absolute addressing is not supported in 64-bit mode

[Jack Howarth]

Tim,
      Thanks. The proposed change applied to the gcc/configure tests
for filds/fists/fildq/fistpq assembler support allows those
instructions to be properly recognized as available on both the
clang-based assembler in Xcode 7 and the legacy GNU assembler in Xcode
6.x and earlier.

https://gcc.gnu.org/bugzilla/attachment.cgi?id=35765

        Jack

On Thu, Jun 11, 2015 at 12:19 PM, Tim Northover <t.p.northover at gmail.com> wrote:
> Hi Jack,
>
> On 11 June 2015 at 08:21, Jack Howarth <howarth.mailing.lists at gmail.com> wrote:
>>    While building FSF gcc 5.1 against Apple's public Xcode 7 beta's
>> new clang-based assembler, I ran into rejected assembly instructions
>> during the -m32 multilb build of libjava.
>
> The diagnostics here don't seem to have changed in Clang, going back
> to even early Xcode 6.
>
>> natArray.s:1110:2: error: ambiguous instructions require an explicit
>> suffix (could be 'filds', or 'fildl')
>>         fild    8(%esi,%edi,2)
>
> This seems reasonable to me. It seems GCC arbitrarily chooses "filds",
> but there's no grand logic behind that decision. I prefer requiring an
> explicit disambiguator.
>
>> clang -cc1as: fatal error: error in backend: 32-bit absolute
>> addressing is not supported in 64-bit mode
>
> Technically, I believe MachO could support such a relocation. But it's
> never one you'd actually want to use because PAGEZERO occupies the low
> 32-bits of the address space as a guard against null pointer accesses.
> So I think this is probably better than the alternative too.
>
> I'd probably suggest making the test use "filds (%ebp)", which should
> assemble in both 32-bit and 64-bit modes and sidesteps the whole
> relocation issue. "filds mem(%rip)" would be a sound 64-bit
> instruction closer to the original, but wouldn't assemble on 32-bit.
>
> Cheers.
>
> Tim.