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Date: Wed, 26 Dec 2001 20:22:21 +0100 (CET)
From: Frank Cornelis <fcorneli@elis.rug.ac.be>
To: Manfred Spraul <manfred@colorfullife.com>
cc: <alad@hss.hns.com>, <linux-kernel@vger.kernel.org>
Subject: Re: Weird __put_user_asm behavior
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Message-ID: <Pine.LNX.4.33.0112262011190.19463-100000@trappist.elis.rug.ac.be>
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Hey,

> The old code evaluates addr once, your new code evaluates it twice.
> Have you tried an inline function instead of a macro?
> linux/fs/binfmt_elf.c contains a few lines that probably break if 'addr' 
> is evaluated twice:
> <<<<<<<
>         argv = (elf_caddr_t *) sp;
>         if (!ibcs) {
>                 __put_user((elf_addr_t)(unsigned long) envp,--sp);
>                 __put_user((elf_addr_t)(unsigned long) argv,--sp);
>         }
> <<<<<<<<<

Double evaluation of the (addr) expression seems to be my problem, not 
register clobbering as I first thought. Although all the macro's that are 
using __put_user_asm also use
	__typeof__(*(addr)) *__their_local_addr = (addr);
	// further use __their_local_addr ...
one apparently needs to repeat this 'localization' of (addr) in order to 
have only one evaluation of (addr) at the end.
I always found the macro paragraph in my first C book -'A Book on C'- a 
little too short :).

Anyway, thanks to all for the help.

Frank.

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