linux-kernel - Re: [RFC][PATCH 5/5] ftrace/x86-32: Add -mfentry support to x86_32 with DYNAMIC

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Date:   Thu, 16 Mar 2017 09:02:10 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC][PATCH 5/5] ftrace/x86-32: Add -mfentry support to x86_32
 with DYNAMIC_FTRACE set

On Thu, 16 Mar 2017 18:24:12 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> > +/* mcount uses a frame pointer even if CONFIG_FRAME_POINTER is not set */
> > +#if !defined(CC_USING_FENTRY) || defined(CONFIG_FRAME_POINTER)
> > +# define USING_FRAME_POINTER
> > +#endif
> > +
> > +#ifdef USING_FRAME_POINTER
> > +# ifdef CC_USING_FENTRY
> > +#  define MCOUNT_FRAME_SIZE		(4*4)	/* bp,ip and parent's  */
> > +# else
> > +#  define MCOUNT_FRAME_SIZE		4	/* just the bp         */
> > +# endif
> > +# define MCOUNT_FRAME			1	/* using frame = true  */
> > +#else
> > +# define MCOUNT_FRAME_SIZE		0	/* no stack frame      */
> > +# define MCOUNT_FRAME			0	/* using frame = false */
> > +#endif  
> 
> It seems that there is no use of MCOUNT_FRAME_SIZE below. Do we really need it?

Hmm, one of the previous versions of my patch required it. I think I
was able to tinker with the code to remove all the use cases of it. But
I never removed the definition. Thanks, I'll fix this too.

-- Steve