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

Florent Revest
2023-02-01T16:36:28Z

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)

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.

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(-)

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2.39.1.519.gcb327c4b5f-goog