[bpf-next,v1,0/8] bpf: BTF support for ksyms

Message

Hao Luo Aug. 19, 2020, 10:40 p.m. UTC

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].

The first 5 patches in this series add support for general kernel
global variables, which includes verifier checking (01/08), libbpf
type checking (03/08) and btf_id resolving (04/08).

The last 3 patches extends that capability further by introducing a
helper bpf_per_cpu_ptr(), which allows accessing kernel percpu vars
correctly (06/08).

The tests of this feature were performed against the extended pahole.
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

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.

Hao Luo (8):
  bpf: Introduce pseudo_btf_id
  bpf: Propagate BPF_PSEUDO_BTF_ID to uapi headers in /tools
  bpf: Introduce help function to validate ksym's type.
  bpf/libbpf: BTF support for typed ksyms
  bpf/selftests: ksyms_btf to test typed ksyms
  bpf: Introduce bpf_per_cpu_ptr()
  bpf: Propagate bpf_per_cpu_ptr() to /tools
  bpf/selftests: Test for bpf_per_cpu_ptr()

 include/linux/bpf.h                           |   3 +
 include/linux/btf.h                           |  26 +++
 include/uapi/linux/bpf.h                      |  52 +++++-
 kernel/bpf/btf.c                              |  25 ---
 kernel/bpf/verifier.c                         | 128 ++++++++++++-
 kernel/trace/bpf_trace.c                      |  18 ++
 tools/include/uapi/linux/bpf.h                |  53 +++++-
 tools/lib/bpf/btf.c                           | 171 ++++++++++++++++++
 tools/lib/bpf/btf.h                           |   2 +
 tools/lib/bpf/libbpf.c                        | 130 +++++++++++--
 .../selftests/bpf/prog_tests/ksyms_btf.c      |  81 +++++++++
 .../selftests/bpf/progs/test_ksyms_btf.c      |  36 ++++
 12 files changed, 665 insertions(+), 60 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