Re: [PATCH V6 08/15] ftrace: Add perf text poke events for ftrace trampolines

[Peter Zijlstra]

On Wed, Apr 22, 2020 at 10:39:06AM +0300, Adrian Hunter wrote:
> On 21/04/20 4:45 pm, Peter Zijlstra wrote:
> > On Sun, Apr 05, 2020 at 11:13:20PM +0300, Adrian Hunter wrote:
> >> Add perf text poke events for ftrace trampolines when created and when
> >> freed.
> > 
> > Maybe also put in a little more detail on the various events. Because
> > arch_ftrace_update_trampoline() can also generate text_poke_bp() events,
> > to update an existing trampoline.
> > 
> > A diagram, like with the kprobes thing perhaps.
> 
> How about adding this:
> 
> There can be 3 text_poke events for ftrace trampolines:
> 
> 1. NULL -> trampoline
>    By ftrace_update_trampoline() when !ops->trampoline
>    Trampoline created
> 
> 2. [e.g. on x86] CALL rel32 -> CALL rel32
>    By arch_ftrace_update_trampoline() when ops->trampoline and
>                         ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP
>    [e.g. on x86] via text_poke_bp() which generates text poke events
>    Trampoline-called function target updated
> 
> 3. trampoline -> NULL
>    By ftrace_trampoline_free() when ops->trampoline and
>                  ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP
>    Trampoline freed

Yes, very nice. Thanks!