Messages in this thread | | | Date | Wed, 25 May 2022 18:26:04 +0100 | From | Mark Rutland <> | Subject | Re: [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic trampoline |
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On Wed, May 25, 2022 at 09:58:45AM -0400, Steven Rostedt wrote: > On Wed, 25 May 2022 13:45:13 +0100 > Mark Rutland <mark.rutland@arm.com> wrote: > > > ... the compiler places 3 NOPs *before* any BTI, and 2 NOPs *after* any BTI, > > still recording the location of the first NOP. So in the two cases we get: > > > > NOP <--- recorded location > > NOP > > NOP > > __func_without_bti: > > NOP > > NOP > > > > NOP <--- recorded location > > NOP > > NOP > > __func_with_bti: > > BTI > > NOP > > NOP > > Are you saying that the above "recorded location" is what we have in > mcount_loc section?
Yes; I'm saying that with this series, the compiler would record that into the mcount_loc section.
Note that's not necessarily what goes into rec->ip, which we can adjust at initialization time to be within the function. We'd need to record the presence/absence of the BTI somewhere (I guess in dyn_arch_ftrace).
> If that's the case, we will need to modify it to point to something that > kallsyms will recognize (ie. sym+0 or greater). Because that will cause > set_ftrace_filter to fail as well.
Yup, understood. Like I mentioned it also wrecks the unwinder and would make it really hard to implement RELIABLE_STACKTRACE.
Just to be clear, I don't think we should follow this specific approach. I just wrote the examples to clarify what was being proposed.
Thanks, Mark.
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