linux-kernel - Re: [PATCH v8 4/8] ppc64 ftrace_with

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Date:	Thu, 11 Feb 2016 20:34:28 +1100
From:	Balbir Singh <bsingharora@...il.com>
To:	Torsten Duwe <duwe@....de>
Cc:	Michael Ellerman <mpe@...erman.id.au>,
	Jiri Kosina <jkosina@...e.cz>, Miroslav Benes <mbenes@...e.cz>,
	Petr Mladek <pmladek@...e.com>, Jessica Yu <jeyu@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org
Subject: Re: [PATCH v8 4/8] ppc64 ftrace_with_regs configuration variables

On Thu, 2016-02-11 at 09:42 +0100, Torsten Duwe wrote:
> On Thu, Feb 11, 2016 at 06:48:17PM +1100, Balbir Singh wrote:
> > On Wed, 2016-02-10 at 17:25 +0100, Torsten Duwe wrote:
> > > +
> > > +echo "int func() { return 0; }" | \
> > > +    $* -S -x c -O2 -p -mprofile-kernel - -o - 2> /dev/null | \
> > > +    sed -n -e '/func:/,/bl _mcount/p' | grep -q TOC
> > > +
> > > +leaf_toc_result=$?
> > > +
> > 
> > leaf_toc_result failed for me with gcc 5. I'll try and grab gcc-6
> > and give the patches a spin
> 
> Don't bother. _All_ gccs are broken in that respect currently.
> AFAIK Anton is working on this. You have to fake the test, like
> static int a; return a++;
> 
> Gcc fails to set the TOC for profiled "leaf" functions, where it
> thinks no global/static symbols are referenced.
> 
> 

Thanks for the quick answer

BTW, do we expect static/non global functions to be called from
patched contexts? I understand that not supporting it will
complicate a patch.

Balbir Singh