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

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Date:	Wed, 4 May 2016 22:22:13 +0200
From:	Borislav Petkov <bp@...e.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	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 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...

sarge:~# gcc --version
gcc (GCC) 3.3.5 (Debian 1:3.3.5-13)
Copyright (C) 2003 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

sarge:~# cat popcnt.c
int main(void)
{
        int a, b;

        asm volatile("popcnt %0, %1" : "=r" (a) : "r" (b));

        return 0;
}
sarge:~# gcc -Wall -o popcnt{,.c}
/tmp/ccHmmgjH.s: Assembler messages:
/tmp/ccHmmgjH.s:14: Error: no such instruction: `popcnt %eax,%eax'
sarge:~#

-- 
Regards/Gruss,
    Boris.

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