linux-kernel - Re: libelf-0.175 breaks objtool

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Date:   Thu, 9 Apr 2020 10:25:14 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-xfs <linux-xfs@...r.kernel.org>
Subject: Re: libelf-0.175 breaks objtool

On Thu, Apr 9, 2020 at 9:41 AM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Tue, Apr 07, 2020 at 08:44:11PM +0200, Arnd Bergmann wrote:
> > That is very possible. The -g has been there since xfs was originally merged
> > back in 2002, and I could not figure out why it was there (unlike the
> > -DSTATIC=""
> > and -DDEBUG flags that are set in the same line).
> >
> > On the other hand, my feeling is that setting -g should not cause problems
> > with objtool, if CONFIG_DEBUG_INFO is ok.
>
> I suspect we shouldn't force -g ourselves in xfs.  Care to send a patch?

Done.

On a related topic, I noticed how the CONFIG_DEBUG flag used to control
whether functions marked STATIC get inlined or not, but now they are always
marked noinline, apparently in an attempt to get more readable object code
even when not debugging. I also see that during early v2.6, XFS used
'STATIC' almost exclusively, while newly added functions tend to use plain
'static' instead.

Is this something worth revisiting to see if inlining would make a difference
to performance or are you reasonably sure it does not?

       Arnd