Date: Mon, 23 Jul 2001 13:18:38 -0700 (PDT) From: John Baldwin <jhb@FreeBSD.org> To: j mckitrick <jcm@FreeBSD-uk.eu.org> Cc: freebsd-chat@FreeBSD.org Subject: RE: stack use preference Message-ID: <XFMail.010723131838.jhb@FreeBSD.org> In-Reply-To: <20010723183331.A55127@dogma.freebsd-uk.eu.org>
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On 23-Jul-01 j mckitrick wrote:
>
> For those of you who write or at one time wrote assembly language programs
> for the x86 cpus, what is your preference for local variable on the stack?
> Do you
>
> (a) push the esp down, then move esp to ebp and allocate memory for local
> vars above the esp?
>
> (b) move esp to ebp first, then push the esp down
>
> (c) real programmers don't need ebp for local vars. They calculate offsets
> from esp on the fly. :-)
>
> It seems (a) would be easier for humans, since all offsets, including
> procedure parameters, would be positive.
>
> However, compilers seem to generate type (b), so parameters are positive
> offsets from ebp, and local vars are negative.
(b), as you can walk back through stack traces when debugging by always looking
at [ebp] to get the previous ebp, and [ebp+4] to get the previous IP.
(Assuming you do the normal:
push %ebp
mov %esp, %ebp
...
leave
ret
This is the convention used with the enter/leave 286+ instructions as well.
--
John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/
PGP Key: http://www.baldwin.cx/~john/pgpkey.asc
"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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