linux-kernel - Re: [RFC][PATCH] ftrace/x86: Remove mcount support

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Date:   Thu, 9 May 2019 22:28:58 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        live-patching@...r.kernel.org,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [RFC][PATCH] ftrace/x86: Remove mcount support

On Thu, 9 May 2019 13:12:55 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, May 9, 2019 at 12:49 PM Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
> > index ed80003ce3e2..2f2bdf0662f8 100644
> > --- a/arch/x86/include/asm/livepatch.h
> > +++ b/arch/x86/include/asm/livepatch.h
> > @@ -26,9 +26,6 @@
> >
> >  static inline int klp_check_compiler_support(void)
> >  {
> > -#ifndef CC_USING_FENTRY
> > -       return 1;
> > -#endif
> >         return 0;
> >  }  
> 
> Please remove this entirely.
> 
> There are now three copies of klp_check_compiler_support(), and all
> three are now trivial "return 0" functions.
> 
> Remove the whole thing, and remove the single use in kernel/livepatch/core.c.
> 
> The only reason for this function existing was literally "mcount isn't
> good enough", so with mcount removed, the function should be removed
> too.
>

As this patch is simply a "remove mcount" patch, I'd like to have the
removal of klp_check_compiler_support() be a separate patch.

Jiri or Josh, care to send a patch on top of this one?

Thanks!

-- Steve