linux-kernel - RE: [RFC PATCH v1 0/5] nolibc x86-64 string functions

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Message-ID: <b6a33f1c9c0544c29904e29b06a7cff8@AcuMS.aculab.com>
Date:   Fri, 1 Sep 2023 14:23:28 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Ammar Faizi' <ammarfaizi2@...weeb.org>, Willy Tarreau <w@....eu>
CC:     Thomas Weißschuh <linux@...ssschuh.net>,
        "Nicholas Rosenberg" <inori@...x.org>,
        Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>,
        Michael William Jonathan <moe@...weeb.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH v1 0/5] nolibc x86-64 string functions

From: Ammar Faizi
> Sent: 01 September 2023 14:06
...
> > You're completely right indeed, reminds me about the copy_up/copy_down
> > that were not used anymore :-)
> 
> I'm an idiot, will fix that. Another attempt as suggested below:
> 
> __asm__ (
> ".section .text.nolibc_memmove\n"
> ".weak memmove\n"
> "memmove:\n"
> "    movq    %rdx, %rcx\n"
> "    movq    %rdi, %rdx\n"
> "    movq    %rdi, %rax\n"

You seem to have confused yourself about whether you are using %eax or %edx.

> "    subq    %rsi, %rdx\n"
> "    cmpq    %rcx, %rdx\n"
> "    jnb     .Lforward_copy\n"

I think I'd fall through to the forwards copy
and not worry about replicating the 'reps movsb' and 'ret'.
IIRC 'cld' can be slow as well.

> "    leaq    -1(%rdi, %rcx, 1), %rdi\n"
> "    leaq    -1(%rsi, %rcx, 1), %rsi\n"
> "    std\n"
> ".Lforward_copy:\n"
> "    rep movsb\n"
> "    cld\n"
> "    ret\n"
> );
> 
> --
> Ammar Faizi

	David

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