linux-kernel - Re: [PATCH v2] lib/decompress_unxz.c: removing all memory helper functions

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Date:	Tue, 12 Jun 2012 13:45:29 -0600
From:	Thavatchai Makphaibulcboke <thavatchai.makpahibulchoke@...com>
To:	Joe Perches <joe@...ches.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Lasse Collin <lasse.collin@...aani.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
	"linux390@...ibm.com" <linux390@...ibm.com>,
	"lethal@...ux-sh.org" <lethal@...ux-sh.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"kaloz@...nwrt.org" <kaloz@...nwrt.org>,
	"jj@...osbits.net" <jj@...osbits.net>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>
Subject: Re: [PATCH v2] lib/decompress_unxz.c: removing all memory helper
 functions

On 06/12/2012 11:40 AM, Joe Perches wrote:
> On Tue, 2012-06-12 at 10:30 -0700, H. Peter Anvin wrote:
>> On 06/12/2012 10:26 AM, Nicolas Pitre wrote:
>>>
>>> Instead of copying, maybe this would be much better to make the content 
>>> of lib/string.c usable in a pre-boot environment.
> 
>> Not sure about that... a lot of it is #ifndef __HAVE_ARCH_* and you
>> *really* want those optimizations on some arches.
> 
> Can __weak be used?
> 

lib/string.c contains a lot of stuff that are not needed in preboot, and
would increase the kernel image size.  I'm not sure if we will be able
to make it usable in pre-boot and only bringing in what is needed by
preboot, withtut unnecessarily complicated lib/string.c.

Thanks Joe for the suggestion.  I guess we could remove the #ifndef by
renaming all arch specific mem helper functions to arch_<name>, and
declaring them with a weak attribute in mem.c and let the mem.c check to
see if it is provided, Here is an example for memcpy

Architecture specific,

void *arch_memcpy(void *__dest, __const void *__src, size_t __n)
{
...
}


lib/mem.c

extern void *arch_memcpy(void *__dest, __const void *__src, size_t __n)
__attribute __((weak));

void *memcpy(void *__dest, __const void *__src, size_t __n)
{
        if (arch_memcpy) {
		arch_memcpgoogly();
		return;	
	}

}

But this does not solve the memmove issue. Could we always trust
arch_memcpy in all architectures?  I guess the safest way would be to
use memmove in string.c.  Please let me know if you have any thoughts or
suggestions.

Thanks,
Mak.

.
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