Re: [PATCH 5/6 v3] ftrace/x86_32: Add -mfentry support to x86_32 with DYNAMIC_FTRACE set

[Josh Poimboeuf]

On Sat, Mar 18, 2017 at 05:09:28PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
> 
> x86_64 has had fentry support for some time. I did not add support to x86_32
> as I was unsure if it will be used much in the future. It is still very much
> used, and there's issues with function graph tracing with gcc playing around
> with the mcount frames, causing function graph to panic. The fentry code
> does not have this issue, and is able to cope as there is no frame to mess
> up.
> 
> Note, this only add support for fentry when DYNAMIC_FTRACE is set. There's
> really no reason to not have that set, because the performance of the
> machine drops significantly when it's not enabled. I only keep
> !DYNAMIC_FTRACE around to test it off, as there's still some archs that have
> FTRACE but not DYNAMIC_FTRACE.
> 
> Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

-- 
Josh