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

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Message-ID: <ZPHh0duonHnyAX6C@biznet-home.integral.gnuweeb.org>
Date:   Fri, 1 Sep 2023 20:06:25 +0700
From:   Ammar Faizi <ammarfaizi2@...weeb.org>
To:     Willy Tarreau <w@....eu>
Cc:     David Laight <David.Laight@...lab.com>,
        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

On Fri, Sep 01, 2023 at 01:46:44PM +0200, Willy Tarreau wrote:
> On Fri, Sep 01, 2023 at 11:34:18AM +0000, David Laight wrote:
> > Isn't that completely broken?
> > 
> > You need to select between forwards and backwards moves.
> > Since forwards moves are preferred it is best to do
> > 	if (dst - src < len)
> > 		backards_copy()
> > 	else
> > 		formwards_copy()
> > 
> > 	David
> 
> 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"
"    subq    %rsi, %rdx\n"
"    cmpq    %rcx, %rdx\n"
"    jnb     .Lforward_copy\n"
"    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