Messages in this thread | | | Date | Tue, 15 Nov 2022 15:48:49 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH v2 0/4] arm64/ftrace: move to DYNAMIC_FTRACE_WITH_ARGS |
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On Tue, Nov 15, 2022 at 10:01:48AM -0500, Steven Rostedt wrote: > On Thu, 3 Nov 2022 17:05:16 +0000 > Mark Rutland <mark.rutland@arm.com> wrote: > > > This series replaces arm64's support for FTRACE_WITH_REGS with support > > for FTRACE_WITH_ARGS. This removes some overhead and complexity, and > > removes some latent issues with inconsistent presentation of struct > > pt_regs (which can only be reliably saved/restored at exception > > boundaries). > > > > The existing FTRACE_WITH_REGS support was added for two major reasons: > > > > (1) To make it possible to use the ftrace graph tracer with pointer > > authentication, where it's necessary to snapshot/manipulate the LR > > before it is signed by the instrumented function. > > > > (2) To make it possible to implement LIVEPATCH in future, where we need > > to hook function entry before an instrumented function manipulates > > the stack or argument registers. Practically speaking, we need to > > preserve the argument/return registers, PC, LR, and SP. > > > > Neither of these requires the full set of pt_regs, and only requires us > > to save/restore a subset of registers used for passing > > arguments/return-values and context/return information (which is the > > minimum set we always need to save/restore today). > > > > As there is no longer a need to save different sets of registers for > > different features, we no longer need distinct `ftrace_caller` and > > `ftrace_regs_caller` trampolines. This allows the trampoline assembly to > > be simpler, and simplifies code which previously had to handle the two > > trampolines. > > > > I've tested this with the ftrace selftests, where there are no > > unexpected failures. > > Were there any "expected" failures?
Ah; sorry, I had meant to include the results here.
With this series applied atop v6.1-rc4 and using the ftrace selftests from that tree, my results were the same as with baseline v6.1-rc4:
| # of passed: 104 | # of failed: 0 | # of unresolved: 7 | # of untested: 0 | # of unsupported: 2 | # of xfailed: 1 | # of undefined(test bug): 0
Where the non-passing tests were:
| [8] Test ftrace direct functions against tracers [UNRESOLVED] | [9] Test ftrace direct functions against kprobes [UNRESOLVED]
... as direct functions aren't supported on arm64 (both before and after this series).
| [16] Generic dynamic event - check if duplicate events are caught [UNSUPPORTED] | [74] event trigger - test inter-event histogram trigger eprobe on synthetic event [UNSUPPORTED]
... which are due to a bug in the tests fixed by:
https://lore.kernel.org/all/20221010074207.714077-1-svens@linux.ibm.com/
... and they both pass with that applied.
| [22] Test trace_printk from module [UNRESOLVED] | [31] ftrace - function trace on module [UNRESOLVED] | [51] Kprobe dynamic event - probing module [UNRESOLVED] | [61] test for the preemptirqsoff tracer [UNRESOLVED]
... which are because my test environment didn't have modules.
| [62] Meta-selftest: Checkbashisms [UNRESOLVED]
... which is irrelevant for this series.
| [65] event trigger - test inter-event histogram trigger expected fail actions [XFAIL]
... which is expected.
[...]
> So I ran this on top of my code through all my ftrace tests (for x86) and > it didn't cause any regressions. > > Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Thanks!
Mark.
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