Date:   Fri, 16 Dec 2022 16:51:48 -0800
From:   Yonghong Song <yhs@...a.com>
To:     "Daniel T. Lee" <danieltimlee@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Yonghong Song <yhs@...com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [bpf-next 0/5] samples: bpf: enhance syscall tracing program



On 12/15/22 3:39 AM, Daniel T. Lee 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.
> 
> 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

Please change 'samples: bpf" to "samples/bpf".
Also, bpf CI reported some new warnings and failures:

https://github.com/kernel-patches/bpf/actions/runs/3708274678/jobs/6285674300

     CLANG-bpf  /tmp/work/bpf/bpf/samples/bpf/tracex4_kern.o
   /tmp/work/bpf/bpf/samples/bpf/xdp_fwd_user.c: In function ‘main’:
   /tmp/work/bpf/bpf/samples/bpf/xdp_fwd_user.c:85:44: warning: ‘_prog’ 
directive output may be truncated writing 5 bytes into a region of size 
between 2 and 9 [-Wformat-truncation=]
      85 |  snprintf(prog_name, sizeof(prog_name), "%s_prog", app_name);
         |                                            ^~~~~
   In file included from /usr/include/stdio.h:867,
                    from /tmp/work/bpf/bpf/samples/bpf/xdp_fwd_user.c:19:
   /usr/include/x86_64-linux-gnu/bits/stdio2.h:67:10: note: 
‘__builtin___snprintf_chk’ output between 13 and 20 bytes into a 
destination of size 16
      67 |   return __builtin___snprintf_chk (__s, __n, 
__USE_FORTIFY_LEVEL - 1,
         | 
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      68 |        __bos (__s), __fmt, __va_arg_pack ());
         |        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     CC      /tmp/work/bpf/bpf/samples/bpf/syscall_nrs.s

...

     CLANG-BPF 
/tmp/work/bpf/bpf/samples/bpf/test_current_task_under_cgroup.bpf.o
   In file included from 
/tmp/work/bpf/bpf/samples/bpf/test_probe_write_user.bpf.c:8:
   In file included from /usr/include/string.h:26:
   In file included from 
/usr/include/x86_64-linux-gnu/bits/libc-header-start.h:33:
   In file included from /usr/include/features.h:485:
   /usr/include/x86_64-linux-gnu/gnu/stubs.h:7:11: fatal error: 
'gnu/stubs-32.h' file not found
   # include <gnu/stubs-32.h>
             ^~~~~~~~~~~~~~~~
   1 error generated.
   make[3]: *** [/tmp/work/bpf/bpf/samples/bpf/Makefile:394: 
/tmp/work/bpf/bpf/samples/bpf/test_probe_write_user.bpf.o] Error 1
   make[3]: *** Waiting for unfinished jobs....
   In file included from 
/tmp/work/bpf/bpf/samples/bpf/map_perf_test.bpf.c:8:
   In file included from /usr/include/errno.h:25:
   In file included from /usr/include/features.h:485:
   /usr/include/x86_64-linux-gnu/gnu/stubs.h:7:11: fatal error: 
'gnu/stubs-32.h' file not found
   # include <gnu/stubs-32.h>
             ^~~~~~~~~~~~~~~~
   1 error generated.
   make[3]: *** [/tmp/work/bpf/bpf/samples/bpf/Makefile:394: 
/tmp/work/bpf/bpf/samples/bpf/map_perf_test.bpf.o] Error 1
   make[2]: *** [/tmp/work/bpf/bpf/Makefile:1994: 
/tmp/work/bpf/bpf/samples/bpf] Error 2
   make[2]: Leaving directory '/tmp/work/bpf/bpf/kbuild-output'
   make[1]: *** [Makefile:231: __sub-make] Error 2
   make[1]: Leaving directory '/tmp/work/bpf/bpf'
   make: *** [Makefile:269: all] Error 2
   make: Leaving directory '/tmp/work/bpf/bpf/samples/bpf'
   Error: Process completed with exit code 2.

Please check bpf ci https://github.com/kernel-patches/bpf
and fix the above issues properly.

> 
>   samples/bpf/Makefile                          | 10 ++--
>   ...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 +-
>   13 files changed, 51 insertions(+), 81 deletions(-)
>   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%)
> 

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