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Date: Thu, 14 Dec 2000 09:51:42 +1100 (EST)
From: Iain Templeton <iain@research.canon.com.au>
To: freebsd-hackers@FreeBSD.ORG
Cc: Alfred Perlstein <bright@wintelcom.net>,
	Drew Eckhardt <drew@PoohSticks.ORG>, Marc Tardif <intmktg@CAM.ORG>
Subject: Re: syscall assembly
In-Reply-To: <20001213142539.R16205@fw.wintelcom.net>
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On Wed, 13 Dec 2000, Alfred Perlstein wrote:

> David, can you look at this?
> 
> #include <fcntl.h>
> 
> int foo() {
>   open("file", O_RDONLY);
>   return 0;
> }
> int main() {
>   int x;
>   x = foo();
>   return 0;
> }
> 
> results in:
> 
> foo:
>         pushl %ebp
>         movl %esp,%ebp
>         subl $8,%esp
>         addl $-8,%esp
>         pushl $0
>         pushl $.LC0
>         call open
>         xorl %eax,%eax
>         leave
>         ret
> 
> why the subl then addl?
> 
Well, as a thoroughly rough guess, the subl is probably to create space
on the stack for the args, and the addl is to align the stack to a 16
byte address?

I know that the PowerPC ABI wants that, but no idea about x86.

Iain



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