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

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Date:	Wed, 4 May 2016 14:09:57 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Borislav Petkov <bp@...e.de>
Cc:	"H. Peter Anvin" <hpa@...or.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>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>,
	Andy Lutomirski <luto@...capital.net>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH] x86/hweight: Get rid of the special calling
 convention

On Wed, May 04, 2016 at 10:22:13PM +0200, Borislav Petkov wrote:
> On Wed, May 04, 2016 at 12:49:17PM -0700, H. Peter Anvin wrote:
> > Sigh.  Doesn't look like -Wa is going to help due to the lack of the
> > equivalent of an -include option in gas.
> 
> So much for the register "freedom" - I'll resurrect the hardcoded insn
> bytes. :-\
> 
> Unless my gcc friends have some other ideas...

You can probe the assembler in the Makefile and pass a define,
like it is done by the dwarf code.  When the define is not
set use the hard coded registers

Not very scalable, but may work in this case.

Longer term would probably need compiler probes at Kconfig
time (this would be useful for a lot of things)

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.