linux-kernel - Re: 64-bit syscall ABI issue

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Message-ID: <4664A87C.5040609@zytor.com>
Date:	Mon, 04 Jun 2007 17:04:12 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Miller <davem@...emloft.net>
CC:	joseph@...esourcery.com, linux-kernel@...r.kernel.org,
	linux-mips@...ux-mips.org, linux-arch@...r.kernel.org
Subject: Re: 64-bit syscall ABI issue

David Miller wrote:
> From: "Joseph S. Myers" <joseph@...esourcery.com>
> Date: Mon, 4 Jun 2007 20:56:57 +0000 (UTC)
> 
> [ added linux-arch which is a great place to discuss these
>   kinds of issues. ]
> 
>> What should the kernel syscall ABI be in such cases (any case where the 
>> syscall implementations expect arguments narrower than registers, so 
>> mainly 32-bit arguments on 64-bit platforms)?  There are two obvious 
>> possibilities:
> 
> In general we've taken the stance that the syscall dispatch
> should create the proper calling environment for C code
> implementing the system calls, and this thus means properly
> sign and zero extending the arguments as expected by the C
> calling convention.

This is, in fact, rather fundamental (some ABIs don't require sign or
zero extension, e.g. x86-64); otherwise libc's job becomes a whole lot
harder.

	-hpa
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