linux-kernel - Re: [PATCH v2] ftrace: Match dot symbols when searching functions on ppc64

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Date:	Tue, 26 Apr 2016 09:36:01 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] ftrace: Match dot symbols when searching functions
 on ppc64

On Mon, 25 Apr 2016 18:56:14 -0300
Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com> wrote:

> In the ppc64 big endian ABI, function symbols point to function
> descriptors. The symbols which point to the function entry points
> have a dot in front of the function name. Consequently, when the
> ftrace filter mechanism searches for the symbol corresponding to
> an entry point address, it gets the dot symbol.
> 
> As a result, ftrace filter users have to be aware of this ABI detail on
> ppc64 and prepend a dot to the function name when setting the filter.
> 
> The perf probe command insulates the user from this by ignoring the dot
> in front of the symbol name when matching function names to symbols,
> but the sysfs interface does not. This patch makes the ftrace filter
> mechanism do the same when searching symbols.
> 
> Fixes the following failure in ftracetest's kprobe_ftrace.tc:
> 
>   .../kprobe_ftrace.tc: line 9: echo: write error: Invalid argument
> 
> That failure is on this line of kprobe_ftrace.tc:
> 
>   echo _do_fork > set_ftrace_filter
> 
> This is because there's no _do_fork entry in the functions list:
> 
>   # cat available_filter_functions | grep _do_fork
>   ._do_fork
> 
> This change introduces no regressions on the perf and ftracetest
> testsuite results.
> 
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
> ---

Acked-by: Steven Rostedt <rostedt@...dmis.org>

This can go through the ppc tree.

-- Steve