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

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Message-ID: <000CE7C8-33F3-404A-9E7D-F2CCB0BA110E@zytor.com>
Date:   Sun, 06 Jan 2019 23:59:10 -0800
From:   hpa@...or.com
To:     Cao jin <caoj.fnst@...fujitsu.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

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.
-- 
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