linux-kernel - Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

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]

Date:	Wed, 11 May 2016 21:54:50 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Brian Gerst <brgerst@...il.com>
CC:	Borislav Petkov <bp@...e.de>, x86-ml <x86@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Andi Kleen <andi@...stfloor.org>, zengzhaoxiu@....com,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On May 11, 2016 4:24:09 AM PDT, Peter Zijlstra <peterz@...radead.org> wrote:
>On Wed, May 11, 2016 at 07:15:19AM -0400, Brian Gerst wrote:
>
>> I think he meant the out of line version would be asm, so you could
>> control what registers were clobbered.
>
>Yeah, it might save a few cycles on the call, but given that most
>machines should have popcnt these days is it worth the hassle/cost of
>duplicating the lib/hweight.c magic in asm (and remember, twice, once
>for 32bit and once for 64bit) ?

I was thinking it isn't really very complex code even in assembly as it is super-regular; you can even crib the gcc-generated code if you wish.
-- 
Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.