Date: Tue, 24 Jul 2001 11:54:18 -0700 (PDT) From: John Baldwin <jhb@FreeBSD.org> To: j mckitrick <jcm@FreeBSD-uk.eu.org> Cc: freebsd-chat@FreeBSD.org, Greg Lehey <grog@FreeBSD.org> Subject: Re: stack use preference Message-ID: <XFMail.010724115418.jhb@FreeBSD.org> In-Reply-To: <20010724022658.A63186@dogma.freebsd-uk.eu.org>
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On 24-Jul-01 j mckitrick wrote:
> IIUC, here is what happens:
>
> foo: ; (int i, char *s)
> push %ebp ; save current stack frame
> mov %esp, %ebp ; make a new one at the current stack pointer
> sub $8, %ebp ; make space for local vars
> mov 8(%ebp), ebx; get char * param
> mov 4(%ebp), eax; get int param
> [...]
> leave
> ret
> ; same as ???
> mov %ebp, %esp ; reset stack pointer
> pop %ebp ; restore old frame
> ret
Yes. On x86, doing
enter $8, $0 ; 8 bytes of local storage
is equivalent to:
push %ebp
mov %esp, %ebp
sub $8, %esp
but most compilers that I've seen unroll 'enter' rather than using it directly.
*shrug*
Thus, you could do:
foo:
enter $8, $0
mov 12(%ebp), %ebx ; get char * param
mov 8(%ebp), %eax ; get int param
; note that 4(%ebp) is the saved IP, not a param
...
leave
ret
> main:
> push %eax ; char *
> push %ebx ; int
> call foo
> [...]
--
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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