From fe879bb42f8a6513ed18e9d22efb99cb35590201 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Mon, 11 Mar 2024 19:32:49 -0700 Subject: bpftool: Fix missing pids during link show 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") Signed-off-by: Yonghong Song Signed-off-by: Andrii Nakryiko Tested-by: Quentin Monnet Reviewed-by: Quentin Monnet Link: https://lore.kernel.org/bpf/20240312023249.3776718-1-yonghong.song@linux.dev --- tools/bpf/bpftool/skeleton/pid_iter.bpf.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'tools/bpf') diff --git a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c index 26004f0c5a6a..7bdbcac3cf62 100644 --- a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c +++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c @@ -102,8 +102,8 @@ 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, - BPF_LINK_TYPE_PERF_EVENT___local)) { + if (BPF_CORE_READ(link, type) == bpf_core_enum_value(enum bpf_link_type___local, + BPF_LINK_TYPE_PERF_EVENT___local)) { e.has_bpf_cookie = true; e.bpf_cookie = get_bpf_cookie(link); } -- cgit v1.2.3