Re: Alignment issue on x86_64?

[Andrew Haley <aph at redhat dot com>]

John Fine wrote:
> Andrew Haley wrote:
>>
>> Then this is probably a bug in gcc.  I'd debug it a bit more
>> then start working on a cut-down test case.
>>   
> Is the idea that this is a bug in gcc based on something specific in the
> ABI?

As far as I can see there's nothing wrong with the C code.  It might be
that there is something else going on, but a cut-down test case will
show that, one way or the other.

> Where is the ABI documentation ?  I tried to find it.  I found GCC C++
> ABI documentation that was too specific to IA64 to be useful otherwise
> (despite comments I found in many other places saying that IA64 ABI
> applies to more than IA64.  I found x86_64 ABI documentation with no
> connection to GCC and little to C++.

The x86_64 ABI is here:
http://refspecs.freestandards.org/elf/x86_64-abi-0.95.pdf

> If the issue of this thread is a gcc bug, you still would need a specify
> ABI (gcc, C++, X86_64) to answer the question of whether it is a bug in
> the compilation of the calling code discussed in this thread vs. a bug
> in the compilation of the called code inside XGetWindowProperty.

> The info posted in this thread is fairly convincing that the issue is
> not a bug in the calling code itself, though I wouldn't rule out the
> possibility that we're all missing something and the bug is actually in
> the calling code.

Me either.  That's why we need a test case.

> Assuming the ABI makes those bits undefined, the bug is in the called
> code (in its source or in the way gcc compiled it) for using undefined
> bits, not in the compilation of the calling code.

If so, it's a gcc bug either way.  Both caller and callee were compiled
by gcc.  But we don't have enough information to determine what the cause
of the problem really is.

Andrew.