[PATCHv2 bpf-next 0/5] bpf: Add helpers to access traced function arguments

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)

v2 changes:
  - added acks
  - updated stack diagram
  - return -EOPNOTSUPP instead of -EINVAL in bpf_get_func_ret
  - removed gpl_only for all helpers
  - added verifier fix to allow proper arguments checks,
    Andrii asked for checking also 'int *b' argument in
    bpf_modify_return_test programs and it turned out that it's currently
    not supported by verifier - we can't read argument that is int pointer,
    so I had to add verifier change to allow that + adding verifier selftest
  - checking all arguments in bpf_modify_return_test test programs
  - moved helpers proto gets in tracing_prog_func_proto with attach type check

thanks,
jirka


[1] https://lore.kernel.org/bpf/20211118112455.475349-1-jolsa@kernel.org/ (local)
---
Jiri Olsa (5):
      bpf: Allow access to int pointer arguments in tracing programs
      selftests/bpf: Add test to access int ptr argument in tracing program
      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/linux/bpf.h                                         |   5 ++++
 include/uapi/linux/bpf.h                                    |  28 +++++++++++++++++++++
 kernel/bpf/btf.c                                            |   7 +++---
 kernel/bpf/trampoline.c                                     |   8 ++++++
 kernel/bpf/verifier.c                                       |  77 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
 kernel/trace/bpf_trace.c                                    |  55 ++++++++++++++++++++++++++++++++++++++++-
 tools/include/uapi/linux/bpf.h                              |  28 +++++++++++++++++++++
 tools/testing/selftests/bpf/prog_tests/get_func_args_test.c |  44 +++++++++++++++++++++++++++++++++
 tools/testing/selftests/bpf/progs/get_func_args_test.c      | 123 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 tools/testing/selftests/bpf/verifier/btf_ctx_access.c       |  12 +++++++++
 11 files changed, 418 insertions(+), 24 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
 create mode 100644 tools/testing/selftests/bpf/verifier/btf_ctx_access.c