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

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Date:	Wed, 11 May 2016 07:15:19 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Borislav Petkov <bp@...e.de>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>, 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 Wed, May 11, 2016 at 12:11 AM, Borislav Petkov <bp@...e.de> wrote:
> On Tue, May 10, 2016 at 03:30:48PM -0700, H. Peter Anvin wrote:
>> I didn't mean inline assembly.
>
> How does that matter?
>
> The problem is having as less insn bytes as possible and the minimal
> size we can do is issuing POPCNT everywhere which is 4 or 5 bytes. The
> alternatives then replace that with a CALL which is also 5 bytes.
>
> The way I did it now, it adds 22K more to allyesconfig vmlinux due to
> the static_cpu_has doubled alternatives sections and the JMPs. The
> thunks will keep those 5 bytes *and* get rid of the calling convention
> without the growth.
>
> Or?

I think he meant the out of line version would be asm, so you could
control what registers were clobbered.

--
Brian Gerst