linux-kernel - Re: [PATCHv2 2/8] module/ftrace: handle patchable-function-entry

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Date:   Thu, 31 Oct 2019 13:00:22 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Torsten Duwe <duwe@...e.de>
Cc:     linux-arm-kernel@...ts.infradead.org, Jessica Yu <jeyu@...nel.org>,
        Helge Deller <deller@....de>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        linux-kernel@...r.kernel.org, amit.kachhap@....com,
        catalin.marinas@....com, james.morse@....com, jpoimboe@...hat.com,
        jthierry@...hat.com, linux-parisc@...r.kernel.org,
        mingo@...hat.com, peterz@...radead.org, rostedt@...dmis.org,
        svens@...ckframe.org, takahiro.akashi@...aro.org, will@...nel.org
Subject: Re: [PATCHv2 2/8] module/ftrace: handle patchable-function-entry

On Thu, Oct 31, 2019 at 12:42:23PM +0100, Torsten Duwe wrote:
> On Thu, Oct 31, 2019 at 09:02:32AM +0000, Mark Rutland wrote:
> > I agree that the CC_USING_PATCHABLE_FUNCTION_ENTRY ifdeffery could be
> > simplified, and that it would be nice to consistently use
> > FTRACE_CALLSITE_SECTION if we can. However, the generic linker script doesn't
> > include anything, and I don't see a good location for that to live.
> > 
> > What I could do is add an explicit comment:
> > 
> > /*
> >  * The ftrace call sites are logged to a section whose name depends on the
> >  * compiler option used. A given kernel image will only use one, AKA
> >  * FTRACE_CALLSITE_SECTION. We capture all of them here to avoid header
> >  * dependencies.
> >  */
> > #define MCOUNT_REC()						\
> > 			. = ALIGN(8);				\
> > 			__start_mcount_loc = .;			\
> > 			KEEP(*(__patchable_function_entries))   \
> > 			KEEP(*(__mcount_loc))                   \
> > 			__stop_mcount_loc = .;			
> > 
> > ... which should make the dependency clear. Does that sound good to you?
> 
> Beautiful. I just didn't want to miss the opportunity to have this cleaned
> up as well, and deemed this patch "closest" because of the definition of 
> FTRACE_CALLSITE_SECTION. Put it where you see it fit best.

Sure. I've folded the above into this patch, and pushed out an updated branch:

  https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/ftrace-with-regs

Thanks,
Mark.