From owner-freebsd-hackers  Thu Apr 25 10:13:34 2002
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From: Andrew Gallatin <gallatin@cs.duke.edu>
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Date: Thu, 25 Apr 2002 13:12:53 -0400 (EDT)
To: Kenneth Culver <culverk@alpha.yumyumyum.org>
Cc: <freebsd-hackers@FreeBSD.ORG>
Subject: Re: pushal & ebp
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Kenneth Culver writes:
 > > 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

I don't think so.  The temp its pushing is the stack pointer.  If you
look at the layout of the trap frame, then you'll see tf_isp comes
between tf_ebp & tf_ebx.  I assume tf_isp is the stack pointer, so
that should be OK..

Drew


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