Re: [PATCH 0/8] Add ftrace direct call for arm64

Xu Kuohai
2023-02-02T08:37:49Z

On 2/2/2023 12:34 AM, Florent Revest 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 apply on top of the arm64 tree which contains Mark Rutland's
> series on CALL_OPS [1] under the for-next/ftrace tag.
> > The first three patches consolidate the two existing ftrace APIs for registering
> direct calls. They are split to make the reviewers lives easier but if it'd be a
> preferred style, I'd be happy to squash them in the next revision.
> Currently, there is both a _ftrace_direct and _ftrace_direct_multi API. Apart
> from samples and selftests, there are no users of the _ftrace_direct API left
> in-tree so this deletes it and renames the _ftrace_direct_multi API to
> _ftrace_direct for simplicity.
>
> The main benefit of this refactoring is that, with the API that's left, an
> ftrace_ops backing a direct call will only ever point to one direct call. We can
> therefore store the direct called trampoline address in the ops (patch 4) and
> look it up from the ftrace trampoline on arm64 (patch 7) in the case when the
> destination would be out of reach of a BL instruction at the ftrace callsite.
> (in this case, ftrace_caller acts as a lightweight intermediary trampoline)
>
> This series has been tested on both arm64 and x86_64 with:
> 1- CONFIG_FTRACE_SELFTEST (cf: patch 6)
> 2- samples/ftrace/*.ko (cf: patch 8)
> 3- tools/testing/selftests/bpf/test_progs (both -t lsm and -t fentry_fexit)

so it's time to update DENYLIST.aarch64 to unblock tests that failed due to lack of direct call.

>
> This follows up on prior art by Xu Kuohai [2].
> The implementation here is totally different but the fix for ftrace selftests
> (patch 6) is a trivial rebase of a patch originally by Xu so I kept his
> authorship and trailers untouched on that patch, I hope that's ok. >

that's ok for me, thanks.

> 1: https://lore.kernel.org/all/20230123134603.1064407-1-mark.rutland@arm.com/
> 2: https://lore.kernel.org/bpf/20220913162732.163631-1-xukuohai@huaweicloud.com/
>
> Florent Revest (7):
> ftrace: Replace uses of _ftrace_direct APIs with _ftrace_direct_multi
> ftrace: Remove the legacy _ftrace_direct API
> ftrace: Rename _ftrace_direct_multi APIs to _ftrace_direct APIs
> ftrace: Store direct called addresses in their ops
> ftrace: Make DIRECT_CALLS work WITH_ARGS and !WITH_REGS
> arm64: ftrace: Add direct call support
> arm64: ftrace: Add direct called trampoline samples support
>
> Xu Kuohai (1):
> ftrace: Fix dead loop caused by direct call in ftrace selftest
>
> arch/arm64/Kconfig | 4 +
> arch/arm64/include/asm/ftrace.h | 24 ++
> arch/arm64/kernel/asm-offsets.c | 6 +
> arch/arm64/kernel/entry-ftrace.S | 70 +++-
> arch/arm64/kernel/ftrace.c | 36 +-
> include/linux/ftrace.h | 51 +--
> kernel/bpf/trampoline.c | 14 +-
> kernel/trace/Kconfig | 2 +-
> kernel/trace/ftrace.c | 433 +-------------------
> kernel/trace/trace_selftest.c | 14 +-
> samples/Kconfig | 2 +-
> samples/ftrace/ftrace-direct-modify.c | 41 +-
> samples/ftrace/ftrace-direct-multi-modify.c | 44 +-
> samples/ftrace/ftrace-direct-multi.c | 28 +-
> samples/ftrace/ftrace-direct-too.c | 35 +-
> samples/ftrace/ftrace-direct.c | 33 +-
> 16 files changed, 333 insertions(+), 504 deletions(-)