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

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Date:   Thu, 9 May 2019 13:12:55 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.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, 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.

                     Linus