Messages in this thread | | | Subject | Re: [PATCH V4 08/13] ftrace: Add perf text poke events for ftrace trampolines | From | Adrian Hunter <> | Date | Wed, 1 Apr 2020 13:42:50 +0300 |
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On 1/04/20 1:09 pm, Peter Zijlstra wrote: > On Wed, Mar 04, 2020 at 11:06:28AM +0200, Adrian Hunter wrote: >> Add perf text poke events for ftrace trampolines when created and when >> freed. > > If I'm not mistaken that ends up like so: > > static void ftrace_update_trampoline(struct ftrace_ops *ops) > { > + unsigned long trampoline = ops->trampoline; > + > arch_ftrace_update_trampoline(ops); > + if (ops->trampoline && ops->trampoline != trampoline && >> + (ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP)) { >> + /* Add to kallsyms before the perf events */ > + ftrace_add_trampoline_to_kallsyms(ops); >> + perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_OOL, >> + ops->trampoline, ops->trampoline_size, false, >> + FTRACE_TRAMPOLINE_SYM); >> + /* >> + * Record the perf text poke event after the ksymbol register >> + * event. >> + */ >> + perf_event_text_poke((void *)ops->trampoline, NULL, 0, >> + (void *)ops->trampoline, >> + ops->trampoline_size); > } > } > > And afaict, that is wrong. > > The thing is; arch_ftrace_update_trampoline() can actually *update* an > existing trampoline, as per the name. Yes it also creates a trampoline > if there isn't one already, but if there already is one, it will modify > it in-place. > > I see the appeal of having this event in generic code; but I'm thinking > you'll need the update even in arch code anyway, at which point it'd > probably be easier to do all of this in arch code.
For x86, we use text_poke_bp for updates which already does text_poke events via text_poke_bp_batch.
It might be reasonable to assume other architectures will also need to put updates through a common text poker which will take care of text_poke events.
The V3 patch had it in arch code but Steven Rostedt asked why it couldn't be in ftrace_update)trampoline, so I moved it.
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