linux-kernel - Re: [PATCH] ftrace: Do not reference symbols in sections without size

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Date:   Tue, 16 Feb 2021 12:04:06 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] ftrace: Do not reference symbols in sections without size

On Mon, Feb 15, 2021 at 09:00:57PM -0500, Steven Rostedt wrote:
> On Mon, 15 Feb 2021 20:06:39 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > Strange, that when I applied this to the latest kernel on a my build
> > system (binutils 2.35), it still created all the necessary mcount
> > locations??
> 
> I know why it worked. If you are using the latest gcc on the latest
> mainline, it will not even bother with recordmcount, and will just
> create the __mcount_loc sections, as latest gcc knows about ftrace.
> 
> (this is what I get for working on a company holiday)
> 
> Since this is a toolchain issue, perhaps the correct thing to do is to
> backport to stable the changes to have it build with -mrecord-mcount if
> the build system enables it.
> 
> If you are using the lastest compilers to build stable releases, and
> that's causing issues, then you should have the stable releases use the
> latest kernel compiler options.
> 
> Greg,
> 
> Can you test the following two backports. It does change the semantics
> of what is built, but then again if you are using a newer compiler to
> build stable kernels, that can change things too.
> 
> 96f60dfa5819a ("trace: Use -mcount-record for dynamic ftrace")
> 07d0408120216 ("tracing: Avoid calling cc-option -mrecord-mcount for every Makefile")
> 
> I attached the backports to 4.4. (just compiled tested, I'll test them more tomorrow)
> 

Yes, they build here for me!

Thanks for this.

Should I also queue these up for 4.9 and 4.14 which do not have these
commits in them either (but somehow do not show the problem, yet)?

thanks,

greg k-h