linux-kernel - Re: [PATCH] recordmcount.pl: add support for __fentry_

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Message-ID: <20131031161826.GH29371@localhost>
Date:	Thu, 31 Oct 2013 16:18:26 +0000
From:	Jamie Iles <jamie.iles@...cle.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Jamie Iles <jamie.iles@...cle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] recordmcount.pl: add support for __fentry__

On Thu, Oct 31, 2013 at 12:09:26PM -0400, Steven Rostedt wrote:
> On Thu, 31 Oct 2013 15:59:58 +0000
> Jamie Iles <jamie.iles@...cle.com> wrote:
> 
> > With gcc 4.6.0 the -mfentry feature places the function profiling call
> > at the start of the function. When this is used, the call is to
> > __fentry__ and not mcount.
> > 
> > Based on 48bb5dc6cd9d30fe0d594947563da1f8bd9abada (ftrace: Make
> > recordmcount.c handle __fentry__).
> 
> Why? All current users of __fentry__ use the C version of recordmcount.
> This just slows down the few archs that still use recordmcount.pl.

Okay, it's probably fair to drop this one then if it's not useful to the 
other arches.  We have a corner case with Ksplice where the C version of 
mcount not writing the section symbol for __mcount_loc causes a problem 
and we fall back to the perl version, but I'll spend some time working 
on fixing that instead.

Thanks,

Jamie
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