Re: AMD64: stack alignment

On Wed, Dec 18, 2013, Michael Abbott wrote:

> Your patch changes the stack base from being 64-byte aligned to
> being only 8-byte aligned which seems backwards and could break
> other code.  I'm afraid I won't adopt your patch into the ST

I have to admit I'm confused by the alignment issue too, but the
ABI for AMD64 states:

=== http://x86-64.org/documentation/abi.pdf (page 17) ===
3.2.2     The Stack Frame
...
    The end of the input argument area shall be aligned on a 16 (32, if __m256
is passed on stack) byte boundary. In other words, the value (%rsp + 8) is
always a multiple of 16 (32) when control is transferred to the function entry
point. The stack pointer, %rsp, always points to the end of the latest allocated
stack frame.
=== cut ===

So this means rsp % 16 == 8 on function entry, but this is not the case
in the debug output (it's rsp % 16 == 0 which looked fine to me until
someone pointed me to the ABI).

Do you have a program for statethreads that uses OpenSSL 1.0.1e
on amd64 with asm code for SHA1?
Maybe I can try to write a small test program (currently it's the
MeTA1 smtp server that triggers the problem) if you would be
interested in looking into this.


PS: the patch that I attached is wrong for FreeBSD as it changes
the stack layout for i386 too (and it is against my MeTA1 version,
not the original 1.9). That was not intended.

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