Re: [bpf-next v2 0/5] samples/bpf: enhance syscall tracing program

Andrii Nakryiko
2022-12-20T22:41:16Z

On Tue, Dec 20, 2022 at 3:59 AM Daniel T. Lee <danieltimlee@gmail.com> wrote:
>
> Syscall tracing using kprobe is quite unstable. Since it uses the exact
> name of the kernel function, the program might broke due to the rename
> of a function. The problem can also be caused by a changes in the
> arguments of the function to which the kprobe connects. This commit
> enhances syscall tracing program with the following instruments.
>
> In this patchset, ksyscall is used instead of kprobe. By using
> ksyscall, libbpf will detect the appropriate kernel function name.
> (e.g. sys_write -> __s390_sys_write). This eliminates the need to worry
> about which wrapper function to attach in order to parse arguments.
> Also ksyscall provides more fine method with attaching system call, the
> coarse SYSCALL helper at trace_common.h can be removed.
>
> Next, BPF_SYSCALL is used to reduce the inconvenience of parsing
> arguments. Since the nature of SYSCALL_WRAPPER function wraps the
> argument once, additional process of argument extraction is required
> to properly parse the argument. The BPF_SYSCALL macro will reduces the
> hassle of parsing arguments from pt_regs.
>
> Lastly, vmlinux.h is applied to syscall tracing program. This change
> allows the bpf program to refer to the internal structure as a single
> "vmlinux.h" instead of including each header referenced by the bpf
> program.
>
> Additionally, this patchset changes the suffix of _kern to .bpf to make
> use of the new compile rule (CLANG-BPF) which is more simple and neat.
> By just changing the _kern suffix to .bpf will inherit the benefit of
> the new CLANG-BPF compile target.
>
> Also, this commit adds dummy gnu/stub.h to the samples/bpf directory.
> This will fix the compiling problem with 'clang -target bpf'.
>
> ---
> Changes in V2:
> - add gnu/stub.h hack to fix compile error with 'clang -target bpf'
>
> Daniel T. Lee (5):
> samples/bpf: use kyscall instead of kprobe in syscall tracing program
> samples/bpf: use vmlinux.h instead of implicit headers in syscall
> tracing program
> samples/bpf: change _kern suffix to .bpf with syscall tracing program
> samples/bpf: fix tracex2 by using BPF_KSYSCALL macro
> samples/bpf: use BPF_KSYSCALL macro in syscall tracing programs
>

Nice set of changes, thanks for cleaning these up! I don't see
anything obviously wrong, but these changes seem to break s390x build
(see [0]), please check what's going on.

[0] https://github.com/kernel-patches/bpf/actions/runs/3740339876/jobs/6348606866

> samples/bpf/Makefile | 10 ++--
> samples/bpf/gnu/stubs.h | 1 +
> ...p_perf_test_kern.c => map_perf_test.bpf.c} | 48 ++++++++-----------
> samples/bpf/map_perf_test_user.c | 2 +-
> ...c => test_current_task_under_cgroup.bpf.c} | 11 ++---
> .../bpf/test_current_task_under_cgroup_user.c | 2 +-
> samples/bpf/test_map_in_map_kern.c | 1 -
> ...ser_kern.c => test_probe_write_user.bpf.c} | 20 ++++----
> samples/bpf/test_probe_write_user_user.c | 2 +-
> samples/bpf/trace_common.h | 13 -----
> ...trace_output_kern.c => trace_output.bpf.c} | 6 +--
> samples/bpf/trace_output_user.c | 2 +-
> samples/bpf/{tracex2_kern.c => tracex2.bpf.c} | 13 ++---
> samples/bpf/tracex2_user.c | 2 +-
> 14 files changed, 52 insertions(+), 81 deletions(-)
> create mode 100644 samples/bpf/gnu/stubs.h
> rename samples/bpf/{map_perf_test_kern.c => map_perf_test.bpf.c} (85%)
> rename samples/bpf/{test_current_task_under_cgroup_kern.c => test_current_task_under_cgroup.bpf.c} (84%)
> rename samples/bpf/{test_probe_write_user_kern.c => test_probe_write_user.bpf.c} (71%)
> delete mode 100644 samples/bpf/trace_common.h
> rename samples/bpf/{trace_output_kern.c => trace_output.bpf.c} (82%)
> rename samples/bpf/{tracex2_kern.c => tracex2.bpf.c} (89%)
>
> --
> 2.34.1
>