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libbpf: Add some details for BTF parsing failures

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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: Ian Rogers <irogers@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240125231840.1647951-1-irogers@google.com
This commit is contained in:
Ian Rogers 2024-01-25 15:18:40 -08:00 committed by Andrii Nakryiko
parent aecaa3ed48
commit f2e4040c82
1 changed files with 18 additions and 4 deletions
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22
tools/lib/bpf/btf.c
View File

@ -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);