On Tue, Mar 12, 2024 at 8:24 AM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>
>
> On 3/12/24 7:01 AM, Quentin Monnet wrote:
> > 2024-03-12 02:32 UTC+0000 ~ Yonghong Song <yonghong.song@xxxxxxxxx>
> >> Current 'bpftool link' command does not show pids, e.g.,
> >> $ tools/build/bpftool/bpftool link
> >> ...
> >> 4: tracing prog 23
> >> prog_type lsm attach_type lsm_mac
> >> target_obj_id 1 target_btf_id 31320
> >>
> >> Hack the following change to enable normal libbpf debug output,
> >> --- a/tools/bpf/bpftool/pids.c
> >> +++ b/tools/bpf/bpftool/pids.c
> >> @@ -121,9 +121,9 @@ int build_obj_refs_table(struct hashmap **map, enum bpf_obj_type type)
> >> /* we don't want output polluted with libbpf errors if bpf_iter is not
> >> * supported
> >> */
> >> - default_print = libbpf_set_print(libbpf_print_none);
> >> + /* default_print = libbpf_set_print(libbpf_print_none); */
> >> err = pid_iter_bpf__load(skel);
> >> - libbpf_set_print(default_print);
> >> + /* libbpf_set_print(default_print); */
> >>
> >> Rerun the above bpftool command:
> >> $ tools/build/bpftool/bpftool link
> >> libbpf: prog 'iter': BPF program load failed: Permission denied
> >> libbpf: prog 'iter': -- BEGIN PROG LOAD LOG --
> >> 0: R1=ctx() R10=fp0
> >> ; struct task_struct *task = ctx->task; @ pid_iter.bpf.c:69
> >> 0: (79) r6 = *(u64 *)(r1 +8) ; R1=ctx() R6_w=ptr_or_null_task_struct(id=1)
> >> ; struct file *file = ctx->file; @ pid_iter.bpf.c:68
> >> ...
> >> ; struct bpf_link *link = (struct bpf_link *) file->private_data; @ pid_iter.bpf.c:103
> >> 80: (79) r3 = *(u64 *)(r8 +432) ; R3_w=scalar() R8=ptr_file()
> >> ; if (link->type == bpf_core_enum_value(enum bpf_link_type___local, @ pid_iter.bpf.c:105
> >> 81: (61) r1 = *(u32 *)(r3 +12)
> >> R3 invalid mem access 'scalar'
> >> processed 39 insns (limit 1000000) max_states_per_insn 0 total_states 3 peak_states 3 mark_read 2
> >> -- END PROG LOAD LOG --
> >> libbpf: prog 'iter': failed to load: -13
> >> ...
> >>
> >> The 'file->private_data' returns a 'void' type and this caused subsequent 'link->type'
> >> (insn #81) failed in verification.
> >>
> >> To fix the issue, restore the previous BPF_CORE_READ so old kernels can also work.
> >> With this patch, the 'bpftool link' runs successfully with 'pids'.
> >> $ tools/build/bpftool/bpftool link
> >> ...
> >> 4: tracing prog 23
> >> prog_type lsm attach_type lsm_mac
> >> target_obj_id 1 target_btf_id 31320
> >> pids systemd(1)
> >>
> >> Fixes: 44ba7b30e84f ("bpftool: Use a local copy of BPF_LINK_TYPE_PERF_EVENT in pid_iter.bpf.c")
> >> Cc: Quentin Monnet <quentin@xxxxxxxxxxxxx>
> >> Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
> >> ---
> >> tools/bpf/bpftool/skeleton/pid_iter.bpf.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
> >> index 26004f0c5a6a..1eb756f8d02e 100644
> >> --- a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
> >> +++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
> >> @@ -102,7 +102,7 @@ int iter(struct bpf_iter__task_file *ctx)
> >> BPF_LINK_TYPE_PERF_EVENT___local)) {
> >> struct bpf_link *link = (struct bpf_link *) file->private_data;
> >>
> >> - if (link->type == bpf_core_enum_value(enum bpf_link_type___local,
> >> + if (BPF_CORE_READ(link, type) == bpf_core_enum_value(enum bpf_link_type___local,
> >> BPF_LINK_TYPE_PERF_EVENT___local)) {
> > Looks good, thank you! Could you please just realign the
> > BPF_LINK_TYPE_PERF_EVENT___local argument on the next line properly?
>
> Will do. thanks.
>
We can fix it up while applying, so don't send another revision. We
are waiting for trees to converge, so applying patches will be delayed
a bit.
> >
> > With that:
> >
> > Tested-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
> > Reviewed-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
