Messages in this thread | | | Date | Tue, 15 Nov 2022 10:01:48 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH v2 0/4] arm64/ftrace: move to DYNAMIC_FTRACE_WITH_ARGS |
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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?
> > I plan to build atop this with subsequent patches to add per-callsite > ftrace_ops, and I'm sending these patches on their own as I think they > make sense regardless. > > Since v1 [1]: > * Change ifdeferry per Steve's request > * Add ftrace_regs_query_register_offset() per Masami's request > * Fix a bunch of typos > > [1] https://lore.kernel.org/lkml/20221024140846.3555435-1-mark.rutland@arm.com > > This series can be found in my 'arm64/ftrace/minimal-regs' branch on > kernel.org: > > https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/ > git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git > > This version is tagged as: > > arm64-ftrace-minimal-regs-20221103
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>
-- Steve
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