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Date: Tue, 12 Jun 2012 13:45:29 -0600
From: Thavatchai Makphaibulcboke <thavatchai.makpahibulchoke@hp.com>
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To: Joe Perches <joe@perches.com>
CC: "H. Peter Anvin" <hpa@zytor.com>, Nicolas Pitre <nicolas.pitre@linaro.org>,
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Subject: Re: [PATCH v2] lib/decompress_unxz.c: removing all memory helper
 functions
References: <1339470307-28223-1-git-send-email-tmac@hp.com>  <20120612191804.4211462a@tukaani.org>  <alpine.LFD.2.02.1206121316190.23555@xanadu.home>  <4FD77CAF.1020402@zytor.com> <1339522812.2404.4.camel@joe2Laptop>
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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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