Messages in this thread | | | Date | Mon, 13 Aug 2012 10:42:45 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC PATCH 0/4] ftrace: Add use of -mfentry for x86_64 |
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* H. Peter Anvin <hpa@zytor.com> wrote:
> On 08/07/2012 12:38 PM, Steven Rostedt wrote: > > > >This is an RFC patch set that makes gcc use the -mfentry option with > >-pg. This will set the ftrace 'hook' to the beginning of the function > >and also remove the requirement that -pg enables frame pointers. > > > >This has a couple of benefits (and probably more). > > > >1) removal of the frame pointer requirement makes for smaller and faster code. > > > >2) Having the function trace hook at the beginning of the function instead > > of after the frame is set up, gives the function tracing callbacks access > > to the parameters. This means that kprobes can take advantage of this. > > When a kprobe is set on top of a ftrace hook (nop), it will automatically > > use the function tracing callback. This makes it into an 'optimized' probe > > as there's no need to hit a breakpoint and trigger the probe that way. > > The function tracing code can do the work for it. Note, optimized probes > > are only allowed with !PREEMPT, but a ftrace optimize probe is allowed > > in any context (another benefit). > > > >This only implements fentry for x86_64. > > > > Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Nice feature!
Thanks,
Ingo
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