Re: [PATCH v4 0/4] Add ftrace direct call for arm64

[Florent Revest]

On Mon, Apr 3, 2023 at 1:21 PM Florent Revest <revest@xxxxxxxxxxxx> wrote:
>
> This series adds ftrace direct call support to arm64.
> This makes BPF tracing programs (fentry/fexit/fmod_ret/lsm) work on arm64.
>
> It is meant to be taken by the arm64 tree but it depends on the
> trace-direct-v6.3-rc3 tag of the linux-trace tree:
>   git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
> That tag was created by Steven Rostedt so the arm64 tree can pull the prior work
> this depends on. [1]
>
> Thanks to the ftrace refactoring under that tag, an ftrace_ops backing a ftrace
> direct call will only ever point to *one* direct call. This means we can look up
> the direct called trampoline address stored in the ops from the ftrace_caller
> trampoline in the case when the destination would be out of reach of a BL
> instruction at the ftrace callsite. This fixes limitations of previous attempts
> such as [2].
>
> This series has been tested on arm64 with:
> 1- CONFIG_FTRACE_SELFTEST
> 2- samples/ftrace/*.ko (cf: patch 3)
> 3- tools/testing/selftests/bpf/test_progs (cf: patch 4)
>
> Changes since v3 [3]:
> - Added "BTI C" instructions at the beginning of each ftrace direct call sample

Ugh, I am an idiot (let's just blame Mondays!) and didn't actually
amend this change, I'm sending the series again as a v5 and this time
with the change actually folded in... Please ignore this v4, sorry for
the noise! :|