[PATCH v6 0/5] Add ftrace direct call for arm64

Florent Revest
2023-04-05T18:03:56Z

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 4)
3- tools/testing/selftests/bpf/test_progs (cf: patch 5)

Changes since v5 [3]:
- Fixed saving the fourth argument of handle_mm_fault in both the x86 (patch 3)
and arm64 (as part of patch 4) "ftrace-direct-too" sample trampolines
- Fixed the address of the traced function logged by some direct call samples
(ftrace-direct-multi and ftrace-direct-multi-modify) by moving lr into x0

1: https://lore.kernel.org/all/ZB2Nl7fzpHoq5V20@FVFF77S0Q05N/
2: https://lore.kernel.org/all/20220913162732.163631-1-xukuohai@huaweicloud.com/
3: https://lore.kernel.org/bpf/20230403113552.2857693-1-revest@chromium.org/

Florent Revest (5):
arm64: ftrace: Add direct call support
arm64: ftrace: Simplify get_ftrace_plt
samples: ftrace: Save required argument registers in sample
trampolines
arm64: ftrace: Add direct call trampoline samples support
selftests/bpf: Update the tests deny list on aarch64

arch/arm64/Kconfig | 6 ++
arch/arm64/include/asm/ftrace.h | 22 +++++
arch/arm64/kernel/asm-offsets.c | 6 ++
arch/arm64/kernel/entry-ftrace.S | 90 ++++++++++++++++----
arch/arm64/kernel/ftrace.c | 46 +++++++---
samples/ftrace/ftrace-direct-modify.c | 34 ++++++++
samples/ftrace/ftrace-direct-multi-modify.c | 40 +++++++++
samples/ftrace/ftrace-direct-multi.c | 24 ++++++
samples/ftrace/ftrace-direct-too.c | 40 +++++++--
samples/ftrace/ftrace-direct.c | 24 ++++++
tools/testing/selftests/bpf/DENYLIST.aarch64 | 82 ++----------------
11 files changed, 306 insertions(+), 108 deletions(-)

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2.40.0.577.gac1e443424-goog