On 3/12/24 4:11 PM, Andrii Nakryiko wrote:
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.
Thanks!
With that:
Tested-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
Reviewed-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
