linux-kernel - Re: [PATCH] lib/decompress_unxz.c: removing all memory helper functions

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Message-ID: <1337881229.5070.29.camel@joe2Laptop>
Date:	Thu, 24 May 2012 10:40:29 -0700
From:	Joe Perches <joe@...ches.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	T Makphaibulchoke <tmac@...com>, lethal@...ux-sh.org,
	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	kaloz@...nwrt.org, matt.fleming@...el.com,
	lasse.collin@...aani.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	linux-sh@...r.kernel.org, linux@....linux.org.uk,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
	linux390@...ibm.com
Subject: Re: [PATCH] lib/decompress_unxz.c: removing all memory helper
 functions

On Thu, 2012-05-24 at 10:29 -0700, H. Peter Anvin wrote:
> On 05/24/2012 10:26 AM, Joe Perches wrote:
> > On Thu, 2012-05-24 at 10:03 -0600, T Makphaibulchoke wrote:
> >> The patch cleans up the file lib/decompress_unxz.c by removing all memory
> >> helper functions, e.g., memmove.  By doing so, any architecture's preboot
> >> environment supporting the XZ decompression needs to define its own copy of
> >> any of the missing memory helper functions.
> > 
> > Perhaps a silly question, but why not use
> > the __builtin variants?
> 
> For a lot of cases the __builtin variants just generate a call to the
> expected out-of-line function, so you need it anyway.

While I'm not completely knowledgeable about gcc,
aren't all the __builtin_mem<foo> functions always
available in gcc 3+

http://gcc.gnu.org/onlinedocs/gcc-3.0.4/gcc_5.html#SEC114

It does say:

Many of these functions are only optimized in certain cases; if not
optimized in a particular case, a call to the library function will be
emitted.

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