From owner-freebsd-hackers  Thu Apr 25  9:23:46 2002
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Date: Thu, 25 Apr 2002 12:22:55 -0400 (EDT)
From: Kenneth Culver <culverk@alpha.yumyumyum.org>
To: Andrew Gallatin <gallatin@cs.duke.edu>
Cc: Peter Wemm <peter@wemm.org>, John Baldwin <jhb@FreeBSD.ORG>,
	<freebsd-hackers@FreeBSD.ORG>
Subject: Re: pushal & ebp
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> I just looked at the NetBSD code & like linux, they use a macro which
> individually pushes the registers onto the stack rather than using
> pushal (which I assume is the same as what intel calls PUSHAD in their
> x86 instruction set ref. manual).
>
> NetBSD stopped using pushal in 1994 in rev 1.85 of their
> arch/i386/i386/locore.s in a commit helpfully documented
> "Don't use pusha and popa."
>
> Does anybody know why the other OSes push the registers individually,
> rather than using pushal?  Could our using pushal be causing Kenneth's
> ebp to get lost, or is this just a red herring?
>
> Thanks,
>
> Drew
>
>
>
according to the intel docs, pushad (or what I'm assuming is pushal in our
case) pushes eax, ecx, edx, ebx then pushes some temporary value (the
original esp I think) then pushes ebp, esi, and edi:

this is from the documentation for pushad

IF OperandSize = 32 (* PUSHAD instruction *)
THEN
Temp  (ESP);
Push(EAX);
Push(ECX);
Push(EDX);
Push(EBX);
Push(Temp);
Push(EBP);
Push(ESI);
Push(EDI);

so could this be the problem?

Ken


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