bpftool: Fix missing pids during link show

Yonghong Song · gregkh · commit 75d015f2f18a · 2024-06-12T11:03:07.000+02:00
[ Upstream commit fe879bb ] 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 torvalds#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: 44ba7b3 ("bpftool: Use a local copy of BPF_LINK_TYPE_PERF_EVENT in pid_iter.bpf.c") Signed-off-by: Yonghong Song <yonghong.song@linux.dev> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Tested-by: Quentin Monnet <quentin@isovalent.com> Reviewed-by: Quentin Monnet <quentin@isovalent.com> Link: https://lore.kernel.org/bpf/20240312023249.3776718-1-yonghong.song@linux.dev Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git 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);
 		}
