[PATCH bpf-next v2 0/9] bpf: make tracing program support multi-link

Menglong Dong
2024-03-11T09:34:28Z

For now, the BPF program of type BPF_PROG_TYPE_TRACING is not allowed to
be attached to multiple hooks, and we have to create a BPF program for
each kernel function, for which we want to trace, even through all the
program have the same (or similar) logic. This can consume extra memory,
and make the program loading slow if we have plenty of kernel function to
trace.

In this series, we add the support to allow attaching a tracing BPF
program to multi hooks, which is similar to BPF_TRACE_KPROBE_MULTI.

In the 1st patch, we add the support to record index of the accessed
function args of the target for tracing program. Meanwhile, we add the
function btf_check_func_part_match() to compare the accessed function args
of two function prototype. This function will be used in the next commit.

In the 2nd patch, we refactor the struct modules_array to ptr_array, as
we need similar function to hold the target btf, target program and kernel
modules that we reference to in the following commit.

In the 3rd patch, we introduce the struct bpf_tramp_link_conn to be the
bridge between bpf_link and trampoline, as the releation between bpf_link
and trampoline is not one-to-one anymore.

In the 4th patch, we add the struct bpf_tramp_multi_link and
bpf_trampoline_multi_{link,unlink}_prog for multi-link of trampoline.

In the 5th patch, we add target btf to the function args of
bpf_check_attach_target(), then the caller can specify the btf to check.

The 6th patch is the main part to add multi-link supporting for tracing.
For now, only the following attach type is supported:

BPF_TRACE_FENTRY_MULTI
BPF_TRACE_FEXIT_MULTI
BPF_MODIFY_RETURN_MULTI

The attach type of BPF_TRACE_RAW_TP has different link type, so we skip
this part in this series for now.

In the 7th and 8th patches, we add multi-link supporting of tracing to
libbpf. Note that we don't free btfs that we load after the bpf programs
are loaded into the kernel now if any programs of type tracing multi-link
existing, as we need to lookup the btf types during attaching.

In the 9th patch, we add the testcases for this series.

Changes since v1:
- According to the advice of Alexei, introduce multi-link for tracing
instead of attaching a tracing program to multiple trampolines with
creating multi instance of bpf_link.

Menglong Dong (9):
bpf: tracing: add support to record and check the accessed args
bpf: refactor the modules_array to ptr_array
bpf: trampoline: introduce struct bpf_tramp_link_conn
bpf: trampoline: introduce bpf_tramp_multi_link
bpf: verifier: add btf to the function args of bpf_check_attach_target
bpf: tracing: add multi-link support
libbpf: don't free btf if program of multi-link tracing existing
libbpf: add support for the multi-link of tracing
selftests/bpf: add testcases for multi-link of tracing

arch/arm64/net/bpf_jit_comp.c | 4 +-
arch/riscv/net/bpf_jit_comp64.c | 4 +-
arch/s390/net/bpf_jit_comp.c | 4 +-
arch/x86/net/bpf_jit_comp.c | 4 +-
include/linux/bpf.h | 51 ++-
include/linux/bpf_verifier.h | 1 +
include/uapi/linux/bpf.h | 10 +
kernel/bpf/bpf_struct_ops.c | 2 +-
kernel/bpf/btf.c | 113 ++++-
kernel/bpf/syscall.c | 425 +++++++++++++++++-
kernel/bpf/trampoline.c | 97 +++-
kernel/bpf/verifier.c | 24 +-
kernel/trace/bpf_trace.c | 48 +-
net/bpf/test_run.c | 3 +
net/core/bpf_sk_storage.c | 2 +
tools/bpf/bpftool/common.c | 3 +
tools/include/uapi/linux/bpf.h | 10 +
tools/lib/bpf/bpf.c | 10 +
tools/lib/bpf/bpf.h | 6 +
tools/lib/bpf/libbpf.c | 215 ++++++++-
tools/lib/bpf/libbpf.h | 16 +
tools/lib/bpf/libbpf.map | 2 +
.../selftests/bpf/bpf_testmod/bpf_testmod.c | 49 ++
.../bpf/prog_tests/tracing_multi_link.c | 153 +++++++
.../selftests/bpf/progs/tracing_multi_test.c | 209 +++++++++
25 files changed, 1366 insertions(+), 99 deletions(-)
create mode 100644 tools/testing/selftests/bpf/prog_tests/tracing_multi_link.c
create mode 100644 tools/testing/selftests/bpf/progs/tracing_multi_test.c

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2.39.2