Commit f2e4040c authored by Ian Rogers's avatar Ian Rogers Committed by Andrii Nakryiko
Browse files

libbpf: Add some details for BTF parsing failures 

As CONFIG_DEBUG_INFO_BTF is default off the existing "failed to find
valid kernel BTF" message makes diagnosing the kernel build issue somewhat
cryptic. Add a little more detail with the hope of helping users.

Before:
```
libbpf: failed to find valid kernel BTF
libbpf: Error loading vmlinux BTF: -3
```

After not accessible:
```
libbpf: kernel BTF is missing at '/sys/kernel/btf/vmlinux', was CONFIG_DEBUG_INFO_BTF enabled?
libbpf: failed to find valid kernel BTF
libbpf: Error loading vmlinux BTF: -3
```

After not readable:
```
libbpf: failed to read kernel BTF from (/sys/kernel/btf/vmlinux): -1
```

Closes: https://lore.kernel.org/bpf/CAP-5=fU+DN_+Y=Y4gtELUsJxKNDDCOvJzPHvjUVaUoeFAzNnig@mail.gmail.com/



Signed-off-by: default avatarIan Rogers <irogers@google.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240125231840.1647951-1-irogers@google.com
parent aecaa3ed

tools/lib/bpf/btf.c

+18 −4
Original line number Diff line number Diff line
@@ -4932,10 +4932,9 @@ static int btf_dedup_remap_types(struct btf_dedup *d) 
 */

struct btf *btf__load_vmlinux_btf(void)

{

	const char *sysfs_btf_path = "/sys/kernel/btf/vmlinux";

	/* fall back locations, trying to find vmlinux on disk */

	const char *locations[] = {

		/* try canonical vmlinux BTF through sysfs first */

		"/sys/kernel/btf/vmlinux",

		/* fall back to trying to find vmlinux on disk otherwise */

		"/boot/vmlinux-%1$s",

		"/lib/modules/%1$s/vmlinux-%1$s",

		"/lib/modules/%1$s/build/vmlinux",
@@ -4949,8 +4948,23 @@ struct btf *btf__load_vmlinux_btf(void) 
	struct btf *btf;

	int i, err;



	uname(&buf);

	/* is canonical sysfs location accessible? */

	if (faccessat(AT_FDCWD, sysfs_btf_path, F_OK, AT_EACCESS) < 0) {

		pr_warn("kernel BTF is missing at '%s', was CONFIG_DEBUG_INFO_BTF enabled?\n",

			sysfs_btf_path);

	} else {

		btf = btf__parse(sysfs_btf_path, NULL);

		if (!btf) {

			err = -errno;

			pr_warn("failed to read kernel BTF from '%s': %d\n", sysfs_btf_path, err);

			return libbpf_err_ptr(err);

		}

		pr_debug("loaded kernel BTF from '%s'\n", path);

		return btf;

	}



	/* try fallback locations */

	uname(&buf);

	for (i = 0; i < ARRAY_SIZE(locations); i++) {

		snprintf(path, PATH_MAX, locations[i], buf.release);