linux-kernel - Re: [PATCH] x86/boot: drop memset from copy.S

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Message-ID: <28158fd7-8569-e0c1-75d0-c423330e256d@cn.fujitsu.com>
Date:   Mon, 7 Jan 2019 16:52:57 +0800
From:   Cao jin <caoj.fnst@...fujitsu.com>
To:     <hpa@...or.com>, <x86@...nel.org>, <linux-kernel@...r.kernel.org>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>
Subject: Re: [PATCH] x86/boot: drop memset from copy.S

Hi,

On 1/7/19 3:59 PM, hpa@...or.com wrote:
> On January 6, 2019 11:40:56 PM PST, Cao jin <caoj.fnst@...fujitsu.com> wrote:
>> According to objdump output of setup, function memset is not used in
>> setup code. Currently, all usage of memset in setup come from macro
>> definition of string.h.
>>
>> Signed-off-by: Cao jin <caoj.fnst@...fujitsu.com>
>> ---
>> Compiled and booted under x86_64; compiled under i386.
>>
>> Questions: now there is 2 definition of memcpy, one lies in copy.S,
>> another lies in string.h which is mapped to gcc builtin function. Do we
>> still need 2 definition? Could we move the content of copy.S to
>> boot/string.c?
>>
>> At first glance, the usage of string.{c.h} of setup is kind of
>> confusing,
>> they are also used in compressed/ and purgatory/
>>
>> arch/x86/boot/copy.S | 15 ---------------
>> 1 file changed, 15 deletions(-)
>>
>> diff --git a/arch/x86/boot/copy.S b/arch/x86/boot/copy.S
>> index 15d9f74b0008..5157d08b0ff2 100644
>> --- a/arch/x86/boot/copy.S
>> +++ b/arch/x86/boot/copy.S
>> @@ -33,21 +33,6 @@ GLOBAL(memcpy)
>> 	retl
>> ENDPROC(memcpy)
>>
>> -GLOBAL(memset)
>> -	pushw	%di
>> -	movw	%ax, %di
>> -	movzbl	%dl, %eax
>> -	imull	$0x01010101,%eax
>> -	pushw	%cx
>> -	shrw	$2, %cx
>> -	rep; stosl
>> -	popw	%cx
>> -	andw	$3, %cx
>> -	rep; stosb
>> -	popw	%di
>> -	retl
>> -ENDPROC(memset)
>> -
>> GLOBAL(copy_from_fs)
>> 	pushw	%ds
>> 	pushw	%fs
> 
> This is dependent on both gcc version and flags.
> 

Thanks for your info, but I still don't quite get your point. All files
who has memset reference in setup will also #include "string.h", so how
gcc version and flags will associate memset reference to the assembly
function by force?  Hope to get a little more details when you are
convenient:)