Re: [PATCH v5 bpf-next 17/21] bpftool: Use syscall/loader program in "prog load" and "gen skeleton" command.

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Wed, May 12, 2021 at 2:33 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> From: Alexei Starovoitov <ast@kernel.org>
>
> Add -L flag to bpftool to use libbpf gen_trace facility and syscall/loader program
> for skeleton generation and program loading.
>
> "bpftool gen skeleton -L" command will generate a "light skeleton" or "loader skeleton"
> that is similar to existing skeleton, but has one major difference:
> $ bpftool gen skeleton lsm.o > lsm.skel.h
> $ bpftool gen skeleton -L lsm.o > lsm.lskel.h
> $ diff lsm.skel.h lsm.lskel.h
> @@ -5,34 +4,34 @@
>  #define __LSM_SKEL_H__
>
>  #include <stdlib.h>
> -#include <bpf/libbpf.h>
> +#include <bpf/bpf.h>
>
> The light skeleton does not use majority of libbpf infrastructure.
> It doesn't need libelf. It doesn't parse .o file.
> It only needs few sys_bpf wrappers. All of them are in bpf/bpf.h file.
> In future libbpf/bpf.c can be inlined into bpf.h, so not even libbpf.a would be
> needed to work with light skeleton.
>
> "bpftool prog load -L file.o" command is introduced for debugging of syscall/loader
> program generation. Just like the same command without -L it will try to load
> the programs from file.o into the kernel. It won't even try to pin them.
>
> "bpftool prog load -L -d file.o" command will provide additional debug messages
> on how syscall/loader program was generated.
> Also the execution of syscall/loader program will use bpf_trace_printk() for
> each step of loading BTF, creating maps, and loading programs.
> The user can do "cat /.../trace_pipe" for further debug.
>
> An example of fexit_sleep.lskel.h generated from progs/fexit_sleep.c:
> struct fexit_sleep {
>         struct bpf_loader_ctx ctx;
>         struct {
>                 struct bpf_map_desc bss;
>         } maps;
>         struct {
>                 struct bpf_prog_desc nanosleep_fentry;
>                 struct bpf_prog_desc nanosleep_fexit;
>         } progs;
>         struct {
>                 int nanosleep_fentry_fd;
>                 int nanosleep_fexit_fd;
>         } links;
>         struct fexit_sleep__bss {
>                 int pid;
>                 int fentry_cnt;
>                 int fexit_cnt;
>         } *bss;
> };
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>  tools/bpf/bpftool/Makefile        |   2 +-
>  tools/bpf/bpftool/gen.c           | 386 ++++++++++++++++++++++++++++--
>  tools/bpf/bpftool/main.c          |   7 +-
>  tools/bpf/bpftool/main.h          |   1 +
>  tools/bpf/bpftool/prog.c          | 107 ++++++++-
>  tools/bpf/bpftool/xlated_dumper.c |   3 +
>  6 files changed, 482 insertions(+), 24 deletions(-)
>

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