[PATCH bpf-next v2] libbpf: fix log level propagation for light skeleton loaders

[Mahe Tardy <mahe.tardy@gmail.com>]

bpftool's -d option is documented to enable bpf_trace_printk() messages
from the generated syscall loader when used with -L as specified in
commit d510296d331a ("bpftool: Use syscall/loader program in "prog load"
and "gen skeleton" command.")

However commit b59e4ce8bcaa ("bpftool: Switch bpf_object__load_xattr()
to bpf_object__load()") changed bpftool to use bpf_object__load() which
call the internal bpf_object_load with extra_log_level to 0 instead of
bpf_object__load_xattr with the user request log_level.

All the plumbing was still there to generate the bpf_trace_printk()
instructions from the generator but was now unreachable because
bpf_gen__init() was called with extra_log_level to 0, leaving
gen->log_level at 0.

This uses the obj->log_level field introduced in commit e0e3ea888c69
("libbpf: Allow passing user log setting through bpf_object_open_opts")
set from reading verifier_logs in do_skeleton(). This preserves both
object-level and explicit load-time logging settings.

Fixes: b59e4ce8bcaa ("bpftool: Switch bpf_object__load_xattr() to bpf_object__load()")
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>
---
This v2 is just a rebase on bpf-next as there was a conflict after the
bpf tree was synched. Daniel suggested to push this to bpf-next as the
libbpf GH repo syncs only from there and added his ack.

 tools/lib/bpf/libbpf.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index c036e8a91ed8..395c4dcb54de 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9144,7 +9144,8 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
 	 * permit cross-endian creation of "light skeleton".
 	 */
 	if (obj->gen_loader) {
-		bpf_gen__init(obj->gen_loader, extra_log_level, obj->nr_programs, obj->nr_maps);
+		bpf_gen__init(obj->gen_loader, obj->log_level | extra_log_level,
+			      obj->nr_programs, obj->nr_maps);
 	} else if (!is_native_endianness(obj)) {
 		pr_warn("object '%s': loading non-native endianness is unsupported\n", obj->name);
 		return libbpf_err(-LIBBPF_ERRNO__ENDIAN);
--
2.34.1