[PATCH bpf-next 0/3] bpf: Add helpers to access traced function arguments

[Jiri Olsa <jolsa@redhat.com>]

hi,
adding new helpers to access traced function arguments that
came out of the trampoline batch changes [1].

  Get n-th argument of the traced function:
    long bpf_get_func_arg(void *ctx, u32 n, u64 *value)
  
  Get return value of the traced function:
    long bpf_get_func_ret(void *ctx, u64 *value)
  
  Get arguments count of the traced funtion:
    long bpf_get_func_arg_cnt(void *ctx)

changes from original post [1]:
  - change helpers names to get_func_*
  - change helpers to return error values instead of
    direct values
  - replaced stack_size usage with specific offset
    variables in arch_prepare_bpf_trampoline
  - add comment on stack layout
  - add more tests
  - allow bpf_get_func_ret in FENTRY programs
  - use BPF_LSH instead of BPF_MUL

thanks,
jirka


[1] https://lore.kernel.org/bpf/20211118112455.475349-1-jolsa@kernel.org/
---
Jiri Olsa (3):
      bpf, x64: Replace some stack_size usage with offset variables
      bpf: Add get_func_[arg|ret|arg_cnt] helpers
      selftests/bpf: Add tests for get_func_[arg|ret|arg_cnt] helpers

 arch/x86/net/bpf_jit_comp.c                                 |  55 +++++++++++++++++++++++++++++++++------------
 include/uapi/linux/bpf.h                                    |  28 +++++++++++++++++++++++
 kernel/bpf/verifier.c                                       |  73 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 kernel/trace/bpf_trace.c                                    |  58 ++++++++++++++++++++++++++++++++++++++++++++++-
 tools/include/uapi/linux/bpf.h                              |  28 +++++++++++++++++++++++
 tools/testing/selftests/bpf/prog_tests/get_func_args_test.c |  38 +++++++++++++++++++++++++++++++
 tools/testing/selftests/bpf/progs/get_func_args_test.c      | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 375 insertions(+), 17 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/get_func_args_test.c
 create mode 100644 tools/testing/selftests/bpf/progs/get_func_args_test.c