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

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Message-ID: <YCvq0hkIvgcKAas2@kroah.com>
Date:   Tue, 16 Feb 2021 16:54:58 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        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 Tue, Feb 16, 2021 at 09:45:39AM -0600, Josh Poimboeuf wrote:
> On Tue, Feb 16, 2021 at 09:51:21AM -0500, Steven Rostedt wrote:
> > On Tue, 16 Feb 2021 12:04:06 +0100
> > Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:
> > 
> > > 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)?
> >
> > This bothers me. I want to know exactly why this is a problem.
> 
> I actually see the same problem with 4.9 and 4.14, using the same
> config.

Ok, that's good to know.

> It's very config-specific.  Something has to convince the toolchain to
> not reference those two weak functions by section.

I've queued up all 3 patches (Steven collapsed 2 into 1 it seems) for
4.4.y, 4.9.y, and 4.14.y now.

> > That said, it is fine to backport those patches, and I would include 4.9
> > and 4.14, as I would think you have a similar requirement that we have in
> > the stable-rt trees. That is you shouldn't experience a regression going
> > from an older kernel to a newer one because the older one had a fix
> > backported to it that a newer one did not. Basically the same rationale that
> > all fixes go into Linus's tree before backporting. We do the same on the
> > stable-rt, where all fixes go in all maintained stable trees that are newer
> > than the one you are backporting to.
> > 
> > Although, it does allow more to be traced than what recordmcount enables.
> > But hopefully it doesn't cause any issues. Maybe I should do some ftrace
> > testing before you go and release any of those stables with those patches.
> > 
> > I'm looking to see if this new "feature" of binutils isn't causing trouble
> > elsewhere. I'm thinking that ftrace is just the canary here.
> 
> It already caused quite a bit of trouble with objtool (as did a previous
> similar change by the Clang assembler).

I feel like we go through this every major binutils release.  Why isn't
"build the Linux kernel" part of the binutils regression test suite by
now?  :)

thanks,

greg k-h