linux-kernel - Re: [PATCH] x86/cpufeature: guard asm_volatile_goto usage with CC_HAVE_ASM

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Message-ID: <20180414101112.GX4064@hirez.programming.kicks-ass.net>
Date:   Sat, 14 Apr 2018 12:11:12 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <ast@...com>
Cc:     Yonghong Song <yhs@...com>, mingo@...nel.org, daniel@...earbox.net,
        linux-kernel@...r.kernel.org, x86@...nel.org, kernel-team@...com,
        Thomas Gleixner <tglx@...utronix.de>,
        netdev <netdev@...r.kernel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH] x86/cpufeature: guard asm_volatile_goto usage with
 CC_HAVE_ASM_GOTO

On Fri, Apr 13, 2018 at 01:42:14PM -0700, Alexei Starovoitov wrote:
> On 4/13/18 11:19 AM, Peter Zijlstra wrote:
> > On Tue, Apr 10, 2018 at 02:28:04PM -0700, Alexei Starovoitov wrote:
> > > Instead of
> > > #ifdef CC_HAVE_ASM_GOTO
> > > we can replace it with
> > > #ifndef __BPF__
> > > or some other name,
> > 
> > I would prefer the BPF specific hack; otherwise we might be encouraging
> > people to build the kernel proper without asm-goto.
> > 
> 
> I don't understand this concern.

The thing is; this will be a (temporary) BPF specific hack. Hiding it
behind something that looks 'normal' (CC_HAVE_ASM_GOTO) is just not
right.