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Date: Thu, 05 May 2016 15:02:37 +0200
From: Denys Vlasenko <dvlasenk@redhat.com>
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To: Borislav Petkov <bp@suse.de>, "H. Peter Anvin" <hpa@zytor.com>
CC: Brian Gerst <brgerst@gmail.com>, LKML <linux-kernel@vger.kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>, Andi Kleen <andi@firstfloor.org>,
        zengzhaoxiu@163.com, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH] x86/hweight: Get rid of the special calling convention
References: <57031D9D.801@gmail.com> <1459934085-7152-1-git-send-email-zengzhaoxiu@163.com> <87wpoay10o.fsf@tassilo.jf.intel.com> <CACT4Y+ZGbzTJj5G1EYW6fcuHxEB8NezfzB9nKBgtBEETpGPtHQ@mail.gmail.com> <20160407094333.GD3866@pd.tnic> <20160504184612.GC23257@pd.tnic> <CAMzpN2h5AroNfCYcmdRCTBQuqBc_r+i+yMqg2aDFQjwYKWZGOA@mail.gmail.com> <5998407c-3497-22c1-45dc-a86afcb73c94@zytor.com> <20160504194101.GE23257@pd.tnic> <f3405f2e-437c-a077-3a1c-90ff31e74787@zytor.com> <20160504202213.GF23257@pd.tnic>
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On 05/04/2016 10:22 PM, 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...
> 
> 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:~#

You are looking at the version of a wrong program.
gcc doesn't process assembly, it generates it.
as is part of binutils, not gcc. "as --version".