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Re: [PATCH] Kill __bzero()

To: Franck Bui-Huu <fbuihuu@gmail.com>
Subject: Re: [PATCH] Kill __bzero()
From: Ralf Baechle <ralf@linux-mips.org>
Date: Mon, 5 Nov 2007 11:24:29 +0000
Cc: linux-mips <linux-mips@linux-mips.org>
In-reply-to: <472D8058.5080209@gmail.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <472D8058.5080209@gmail.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.14 (2007-02-12)
On Sun, Nov 04, 2007 at 09:18:32AM +0100, Franck Bui-Huu wrote:

>   1/ Its unconventional prototype is error prone: its prototype is
>   the same as memset one but was documented by mips_ksym.c like the
>   following:
> 
>          extern void *__bzero(void *__s, size_t __count);
> 
>   2/ For the caller, it makes no difference to call memset instead
>   since it has to setup the second parameter of __bzero to 0.
> 
>   3/ It's not part of the Linux user access API, so no module can use
>   it.
> 
>   4/ It needs to be exported with EXPORT_SYMBOL and therefore consumes
>   some extra bytes.
> 
>   5/ It has only one user.
> 
> Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
> ---
> 
>  I'm wondering if I'm missing something, because this function seems
>  so ugly and useless in the first place, that I can't refrain to
>  submit a patch to get rid of it.

Memset is almost always only ever invoked with a zero argument.  So the
idea was to have something like this:

extern void *__memset(void *__s, int __c, size_t __count);
extern void *bzero(void *__s, size_t __count);

static inline void *memset(void *s, int c, size_t count)
{
        if (__builtin_constant_p(c) && c == 0) {
                bzero(s, count);
                return s;
        } else
                return __memset(s, __c, count);
}

But that was never quite implemented like this as you noticed.

As for the differences in the return value, they're because of of
clear_user and __clear_user which return the number of bytes that could
_not_ be cleared in $a2.  Memset being invoked through the normal C calling
conventions ignores this value while it's the actual result of interest for
__clear_user.

I hope that explains things a little.

  Ralf

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