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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>
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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