[v2] use valid btf in bpf_program__set_attach_target(prog, 0, ...);

Commit Message

Luigi Rizzo Oct. 5, 2020, 10:42 p.m. UTC

bpf_program__set_attach_target() will always fail with fd=0 (attach to a
kernel symbol) because obj->btf_vmlinux is NULL and there is no way to
set it.

Fix this by using libbpf_find_vmlinux_btf_id()

(on a side note: it is unclear whether btf_vmlinux is meant to be
just temporary storage for use in bpf_object__load_xattr(), or
a property of bpf_object, in which case it could be initialuzed
opportunistically, and properly released in bpf_object__close() ).

Signed-off-by: Luigi Rizzo <[e-mail]>
---
 tools/lib/bpf/libbpf.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a4f55f8a460d..33bf102259dd 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10353,9 +10353,8 @@  int bpf_program__set_attach_target(struct bpf_program *prog,
 		btf_id = libbpf_find_prog_btf_id(attach_func_name,
 						 attach_prog_fd);
 	else
-		btf_id = __find_vmlinux_btf_id(prog->obj->btf_vmlinux,
-					       attach_func_name,
-					       prog->expected_attach_type);
+		btf_id = libbpf_find_vmlinux_btf_id(attach_func_name,
+						    prog->expected_attach_type);
 
 	if (btf_id < 0)
 		return btf_id;