[LLVMdev] Intel vs. AT&T Assembly.

[Chris Lattner]

On Sat, 29 Apr 2006, Jeff Cohen wrote:
> We know.  Someone offered to do the Intel version, but did little more than a 
> huge cut and paste of the AT&T version and then lost interest.  No one else 
> has had the time or inclination to finish the (barely begun) job.  Patches 
> accepted :)

Actually, that's not true.  The LLVM X86 backend started out emitting 
intel mode for use with GAS and it's "intel syntax mode" (which does use 
registers with %'s).  Unfortunately GAS has (or commonly available 
versions have) a number of bugs in intel syntax mode (e.g. you can't 
define a function named 'dword'), so we switched to using AT&T syntax.

Intel syntax mode was retained because it's nicer to read :), and because 
it may be useful in the future.  As Jeff says, patches are welcome to make 
it do something useful, e.g. be assemblable with MASM or NASM.

-Chris

> Ralph Corderoy wrote:
>> Hi,
>> 
>> 
>>> It's a long way towards it:
>>> 
>>>     # AT&T.                      # Intel.
>>>             .text                        .text
>>>             .align  16                   .align  16
>>>             .globl  main                 .globl  main
>>>                                          .type   main, @function
>>>     main:                        main:
>>>             subl $12, %esp               sub esp, 12
>>>             fnstcw 10(%esp)              fnstcw word ptr [esp + 10]
>>>             movb $2, 11(%esp)            mov byte ptr [esp + 11], 2
>>>             fldcw 10(%esp)               fldcw word ptr [esp + 10]
>>>             movl 20(%esp), %eax          mov eax, dword ptr [esp + 20]
>>>             movl 4(%eax), %eax           mov eax, dword ptr [eax + 4]
>>> 
>> 
>> Whoops.  I've provided my post-processed version of lli's Intel output
>> which, since I removed the `%' and lowered the `DWORD PTR' isn't a good
>> example.  Still, you get the gist;  there are already significant
>> differences between the two.
>> 
>> Cheers,
>> 
>> 
>> Ralph.
>> 
>> 
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>> 
>> 
>> 
>>

-Chris

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