linux-kernel - Re: [PATCH v2] x86: mostly disable '-maccumulate-outgoing-args'

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Message-ID: <20170322154816.ogk623tpqt7cgjjl@treble>
Date:   Wed, 22 Mar 2017 10:48:16 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     x86@...nel.org, Andy Lutomirski <luto@...capital.net>,
        Pavel Machek <pavel@....cz>,
        kernel list <linux-kernel@...r.kernel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Peter Anvin <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] x86: mostly disable '-maccumulate-outgoing-args'

On Wed, Mar 22, 2017 at 08:51:53AM +0100, Ingo Molnar wrote:
> > +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) && \
> > +	!defined(CC_USING_FENTRY) && \
> > +	!defined(CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE)
> > +# error Your compiler does not support function graph tracing
> > +#endif
> 
> Might make sense to add the compiler option that is missing, i.e. something like:
> 
>   # error Your compiler does not support function graph tracing (-mfentry)
> 
> (or whatever compiler feature is missing.)

I left it vague because otherwise it would need a paragraph :-)

After Steven's latest patches which port fentry to x86-32, I think the
precise version would be:

  # error The following combination is not supported: ((compiler missing -mfentry) || (CONFIG_X86_32 and !CONFIG_DYNAMIC_FTRACE)) && CONFIG_FUNCTION_GRAPH_TRACER && CONFIG_CC_OPTIMIZE_FOR_SIZE.

-- 
Josh