[PATCH v2 bpf-next] libbpf: Improve debug message when the base BTF cannot be found

[Ben Olson <matthew.olson@xxxxxxxxx>]

When running `bpftool` on a kernel module installed in `/lib/modules...`,
this error is encountered if the user does not specify `--base-btf` to
point to a valid base BTF (e.g. usually in `/sys/kernel/btf/vmlinux`).
However, looking at the debug output to determine the cause of the error
simply says `Invalid BTF string section`, which does not point to the
actual source of the error. This just improves that debug message to tell
users what happened.

Signed-off-by: Ben Olson <matthew.olson@xxxxxxxxx>
---

Changed in v2:
  * Made error message better reflect the condition

 tools/lib/bpf/btf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 12468ae0d573..a4ae2df68b91 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -283,7 +283,7 @@ static int btf_parse_str_sec(struct btf *btf)
     return -EINVAL;
   }
   if (!btf->base_btf && start[0]) {
-    pr_debug("Invalid BTF string section\n");
+    pr_debug("Malformed BTF string section, did you forget to provide base BTF?\n");
     return -EINVAL;
   }
   return 0;
--
2.47.0