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

[Florent Revest]

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
- Added Mark Rutland's Acked-by to patch 2

1: https://lore.kernel.org/all/ZB2Nl7fzpHoq5V20@FVFF77S0Q05N/
2: https://lore.kernel.org/all/20220913162732.163631-1-xukuohai@xxxxxxxxxxxxxxx/
3: https://lore.kernel.org/bpf/20230324171451.2752302-1-revest@xxxxxxxxxxxx/

Florent Revest (4):
  arm64: ftrace: Add direct call support
  arm64: ftrace: Simplify get_ftrace_plt
  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        | 32 +++++++
 samples/ftrace/ftrace-direct-multi-modify.c  | 36 ++++++++
 samples/ftrace/ftrace-direct-multi.c         | 22 +++++
 samples/ftrace/ftrace-direct-too.c           | 25 ++++++
 samples/ftrace/ftrace-direct.c               | 23 +++++
 tools/testing/selftests/bpf/DENYLIST.aarch64 | 82 ++----------------
 11 files changed, 288 insertions(+), 102 deletions(-)

-- 
2.40.0.423.gd6c402a77b-goog