libbpf: Improve debug message when the base BTF cannot be found

JIRA: https://issues.redhat.com/browse/RHEL-78201

commit 9a17db5
Author: Ben Olson <matthew.olson@intel.com>
Date:   Tue Nov 26 14:08:45 2024 -0600

    libbpf: Improve debug message when the base BTF cannot be found

    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@intel.com>
    Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
    Link: https://lore.kernel.org/bpf/Z0YqzQ5lNz7obQG7@bolson-desk
    Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

Author: jeromemarchand

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;