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From: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
Date: Wed, 30 Aug 2023 21:08:05 +0700
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Subject: Re: [RFC PATCH v1 2/5] tools/nolibc: x86-64: Use `rep stosb` for `memset()`
To: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Cc: Willy Tarreau <w@1wt.eu>, =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= <linux@weissschuh.net>, 
	Nicholas Rosenberg <inori@vnlx.org>, Michael William Jonathan <moe@gnuweeb.org>, 
	"GNU/Weeb Mailing List" <gwml@vger.gnuweeb.org>, 
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, Aug 30, 2023 at 8:57=E2=80=AFPM Ammar Faizi wrote:
> +".section .text.nolibc_memset\n"
> +".weak memset\n"
> +"memset:\n"
> +       "movq %rsi, %rax\n"
> +       "movq %rdx, %rcx\n"
> +       "movq %rdi, %rdx\n"
> +       "rep stosb\n"
> +       "movq %rdx, %rax\n"
> +       "retq\n"

The first instruction could be:

   movl %esi, %eax

That's smaller. Also, the second argument of memset() is an int
anyway, so there is no need to have a full 64-bit copy of %rsi in
%rax.

-- Viro