[bpf-next,v3,0/6] bpf: BTF support for ksyms

Message

Hao Luo Sept. 16, 2020, 10:35 p.m. UTC

v2 -> v3:
 - Rename functions and variables in verifier for better readability.
 - Stick to logging message convention in libbpf.
 - Move bpf_per_cpu_ptr and bpf_this_cpu_ptr from trace-specific
   helper set to base helper set.
 - More specific test in ksyms_btf.
 - Fix return type cast in bpf_*_cpu_ptr.
 - Fix btf leak in ksyms_btf selftest.
 - Fix return error code for kallsyms_find().

v1 -> v2:
 - Move check_pseudo_btf_id from check_ld_imm() to
   replace_map_fd_with_map_ptr() and rename the latter.
 - Add bpf_this_cpu_ptr().
 - Use bpf_core_types_are_compat() in libbpf.c for checking type
   compatibility.
 - Rewrite typed ksym extern type in BTF with int to save space.
 - Minor revision of bpf_per_cpu_ptr()'s comments.
 - Avoid using long in tests that use skeleton.
 - Refactored test_ksyms.c by moving kallsyms_find() to trace_helpers.c
 - Fold the patches that sync include/linux/uapi and
   tools/include/linux/uapi.

rfc -> v1:
 - Encode VAR's btf_id for PSEUDO_BTF_ID.
 - More checks in verifier. Checking the btf_id passed as
   PSEUDO_BTF_ID is valid VAR, its name and type.
 - Checks in libbpf on type compatibility of ksyms.
 - Add bpf_per_cpu_ptr() to access kernel percpu vars. Introduced
   new ARG and RET types for this helper.

This patch series extends the previously added __ksym externs with
btf support.

Right now the __ksym externs are treated as pure 64-bit scalar value.
Libbpf replaces ld_imm64 insn of __ksym by its kernel address at load
time. This patch series extend those externs with their btf info. Note
that btf support for __ksym must come with the kernel btf that has
VARs encoded to work properly. The corresponding chagnes in pahole
is available at [1] (with a fix at [2] for gcc 4.9+).

The first 3 patches in this series add support for general kernel
global variables, which include verifier checking (01/06), libpf
support (02/06) and selftests for getting typed ksym extern's kernel
address (03/06).

The next 3 patches extends that capability further by introducing
helpers bpf_per_cpu_ptr() and bpf_this_cpu_ptr(), which allows accessing
kernel percpu variables correctly (04/06 and 05/06).

The tests of this feature were performed against pahole that is extended
with [1] and [2]. For kernel BTF that does not have VARs encoded, the
selftests will be skipped.

[1] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?id=f3d9054ba8ff1df0fc44e507e3a01c0964cabd42
[2] https://www.spinics.net/lists/dwarves/msg00451.html



Hao Luo (6):
  bpf: Introduce pseudo_btf_id
  bpf/libbpf: BTF support for typed ksyms
  selftests/bpf: ksyms_btf to test typed ksyms
  bpf: Introduce bpf_per_cpu_ptr()
  bpf: Introduce bpf_this_cpu_ptr()
  bpf/selftests: Test for bpf_per_cpu_ptr() and bpf_this_cpu_ptr()

 include/linux/bpf.h                           |   6 +
 include/linux/bpf_verifier.h                  |   7 +
 include/linux/btf.h                           |  26 +++
 include/uapi/linux/bpf.h                      |  67 +++++-
 kernel/bpf/btf.c                              |  25 ---
 kernel/bpf/helpers.c                          |  32 +++
 kernel/bpf/verifier.c                         | 190 ++++++++++++++++--
 kernel/trace/bpf_trace.c                      |   4 +
 tools/include/uapi/linux/bpf.h                |  67 +++++-
 tools/lib/bpf/libbpf.c                        | 112 +++++++++--
 .../testing/selftests/bpf/prog_tests/ksyms.c  |  38 ++--
 .../selftests/bpf/prog_tests/ksyms_btf.c      |  88 ++++++++
 .../selftests/bpf/progs/test_ksyms_btf.c      |  55 +++++
 tools/testing/selftests/bpf/trace_helpers.c   |  27 +++
 tools/testing/selftests/bpf/trace_helpers.h   |   4 +
 15 files changed, 653 insertions(+), 95 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_ksyms_btf.c