[Zlib-devel] HEADS UP: Apparent bad compilation under (just released) GCC 4.5.0

[Török Edwin]

On 05/11/2010 11:33 PM, Jesus Cea wrote:
> On 11/05/10 22:27, Jesus Cea wrote:
>> Psyco exposes the bug, but the problem is GCC using MMX/SSE and
>> expecting the stack be 16 byte aligned, where the ABI only requires 4
>> byte aligned.
> 
> I was wondering if the testsuite in ZLIB should missalign stack on
> purpose (stack aligned to 4 bytes but not to 16 bytes) to catch&burn
> this issue as early as possible.

How do you know if the platform guarantees 16-byte alignment or not?
I tried to follow that discussion on bugzilla, and lost track who is
right, who is wrong and which ABI applies in this case on Linux.

> 
> And yes, I know that this is not a ZLIB issue, but a GCC one.
> 
> Bah, forget it.

GCC could have inserted some code to check its assumptions, or at least
have such a flag for debugging. I think I'll file such a bugzilla request.

Maybe there is a ABI/C standard that allows them to do these
assumptions/optimizations, but breaking programs on purpose is certainly
not a useful optimization.

Best regards,
--Edwin