x86 32-bits compiler use on a 64-bits machine ?

[Tom St Denis]

Christophe LYON wrote:
> Hi Andrew,
>
> Thanks for your answer.
>
>>> The documentation only mentions the size of int and pointer types.
>>
>> The gcc documentation talks only about gcc; you're asking about the
>> system linker.
>>
>
> I did not mean that.
> If I compile a.c with "gcc-x.x.x (32 bits)" on a Pentium 4 machine, 
> and with "gcc-x.x.x (64 bits) -m32" on an Opteron, am I guaranteed 
> that both a.o will have the same contents?
> Any risk that the file compiled on Opteron contains Opteron-only 
> instructions for instance? Or references only 64 bits variants of some 
> system structures?

If you use -m32 it will be x86_32 code, sections, etc.  You should be 
able to link it with a 32-bit binutils just fine (provided your on the 
same revision of GCC, e.g. don't mix a 32-bit GCC 3.2 with a 64-bit GCC 
4.3).

You won't be guaranteed to get the same object code (byte for byte) 
unless you have the exact same configuration for GCC and revision. 
> If I compile a.c with "gcc-x.x.x (32 bits)" on a Pentium 4 machine, 
> and b.c with "gcc-x.x.x (64 bits) -m32" on an Opteron, I need to be 
> able to link a.o and b.o together and that the result is actually 
> meaningful on a Pentium 4.

Linking should be no problem provided they're the same revision.  Also 
helps to build your 64-bit GCC with multi-lib enabled.

Tom