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

From: Hao Luo
Date: Wed Sep 16 2020 - 18:37:58 EST

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
- 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

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