Messages in this thread | | | Date | Wed, 1 Apr 2020 12:09:55 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH V4 08/13] ftrace: Add perf text poke events for ftrace trampolines |
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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.
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