Alignment on x86

[Andreas Bauer <baueran at in dot tum dot de>]

Hi,

I'm in the process of adding a new call sequence to GCC 3.2 at the
moment, implementing a more general sibcall optimisation on Intel
platforms (and later others, too).  However, I'm wondering where I can
find the right documentation on byte alignment for the stack.

What are the boundaries GCC tries to allocate for each stack frame?  I've
always thought it was 16 byte alignment, and if a function has a few bytes
for locals and args, then the rest are aligned as padding.  But now I've
run into a few examples where I can't grasp the rationale anymore, behind
the amount of bytes allocated on the stack.

Any comments, links, hints to literature, etc. would be appreciated.

Thanks in advance,
Andi.