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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <0d4effd9255143d6a7d90b5b37f01cdb@AcuMS.aculab.com>
Date:   Fri, 1 Sep 2023 14:54:56 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Ammar Faizi' <ammarfaizi2@...weeb.org>
CC:     Willy Tarreau <w@....eu>,
        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 15:42
...
> > > "    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.
> 
> What do you mean? They're all 64-bit pointers.

%ax, %eax, %rax - what is the difference :-)

> What I know is that the %rdx will be clobbered by "subq %rsi, %rdx"
> below and the %rax should be return value. That's why I copy the %rdi
> twice. memmove() returns the dst pointer. Did I miss something?

I'd forgotten about the (stupid) return value.

I'm pretty sure it is an accident from the original pdp-11
implementation from the days before C had an explicit 'return'
statement.
(The pdp-11 I used ran RSX/11M - so had a Fortran compiler
not a C one.)

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)