Date: Wed, 13 Dec 2000 14:10:23 -0800 From: Alfred Perlstein <bright@wintelcom.net> To: Marc Tardif <intmktg@CAM.ORG> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: syscall assembly Message-ID: <20001213141023.O16205@fw.wintelcom.net> In-Reply-To: <Pine.LNX.4.10.10012131620390.12420-100000@Gloria.CAM.ORG>; from intmktg@CAM.ORG on Wed, Dec 13, 2000 at 04:25:46PM -0500 References: <Pine.LNX.4.10.10012131620390.12420-100000@Gloria.CAM.ORG>
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* Marc Tardif <intmktg@CAM.ORG> [001213 13:30] wrote:
> Considering the following C code:
>
> #include <fcntl.h>
> int main() {
> open("file", O_RDONLY);
> return 0;
> }
>
> compiled with gcc -S -O2, the following
> assembly code is generated:
>
> main:
> pushl %ebp
> movl %esp,%ebp
> subl $8,%esp
> addl $-8,%esp
> pushl $0
> pushl $.LC0
> call open
> xorl %eax,%eax
> leave
>
> What is the purpose of the subl and addl
> instructions? On Linux, they are simply
> unexistent..
FreeBSD passes syscall args on the stack, Linux uses registers.
--
-Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]
"I have the heart of a child; I keep it in a jar on my desk."
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