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

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Date:	Tue, 10 May 2016 21:10:42 +0200
From:	Borislav Petkov <bp@...e.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, x86-ml <x86@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.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 Tue, May 10, 2016 at 12:03:48PM -0700, H. Peter Anvin wrote:
> Also, to be fair... if the problem is with these being in C then we
> could just do it in assembly easily enough.

I thought about converting the __sw_hweight* variants to asm but
__sw_hweight32, for example, is 55 bytes here and that's a lot.

Or do you have a better idea?

peterz's sounds ok to me: we call a thunk which then calls __sw_hweight*
after having saved regs properly - problem solved.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--