As CONFIG_DEBUG_INFO_BTF is default off the existing "failed to find valid kernel BTF" message makes diagnosing the kernel build issue some what 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: access to canonical vmlinux (/sys/kernel/btf/vmlinux) to load BTF failed: No such file or directory libbpf: was CONFIG_DEBUG_INFO_BTF enabled? libbpf: failed to find valid kernel BTF libbpf: Error loading vmlinux BTF: -3 ``` After not readable: ``` libbpf: unable to read canonical vmlinux (/sys/kernel/btf/vmlinux): Permission denied libbpf: failed to find valid kernel BTF libbpf: Error loading vmlinux BTF: -3 ``` Closes: https://lore.kernel.org/bpf/CAP-5=fU+DN_+Y=Y4gtELUsJxKNDDCOvJzPHvjUVaUoeFAzNnig@xxxxxxxxxxxxxx/ Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx> --- v3. Try to address review comments from Andrii Nakryiko. --- tools/lib/bpf/btf.c | 35 +++++++++++++++++++++++++++-------- 1 file changed, 27 insertions(+), 8 deletions(-) diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index ec92b87cae01..45983f42aba9 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c @@ -4932,10 +4932,9 @@ static int btf_dedup_remap_types(struct btf_dedup *d) */ struct btf *btf__load_vmlinux_btf(void) { + const char *canonical_vmlinux = "/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", @@ -4946,14 +4945,34 @@ struct btf *btf__load_vmlinux_btf(void) }; char path[PATH_MAX + 1]; struct utsname buf; - struct btf *btf; + struct btf *btf = NULL; int i, err; - uname(&buf); + /* is canonical sysfs location accessible? */ + err = faccessat(AT_FDCWD, canonical_vmlinux, F_OK, AT_EACCESS); + if (err) { + pr_warn("access to canonical vmlinux (%s) to load BTF failed: %s\n", + canonical_vmlinux, strerror(errno)); + pr_warn("was CONFIG_DEBUG_INFO_BTF enabled?\n"); + } else { + err = faccessat(AT_FDCWD, canonical_vmlinux, R_OK, AT_EACCESS); + if (err) { + pr_warn("unable to read canonical vmlinux (%s): %s\n", + canonical_vmlinux, strerror(errno)); + } + } + if (!err) { + /* load canonical and return any parsing failures */ + btf = btf__parse(canonical_vmlinux, NULL); + err = libbpf_get_error(btf); + pr_debug("loading kernel BTF '%s': %d\n", canonical_vmlinux, err); + return btf; + } + /* try fallback locations */ + uname(&buf); for (i = 0; i < ARRAY_SIZE(locations); i++) { snprintf(path, PATH_MAX, locations[i], buf.release); - if (faccessat(AT_FDCWD, path, R_OK, AT_EACCESS)) continue; @@ -4965,9 +4984,9 @@ struct btf *btf__load_vmlinux_btf(void) return btf; } - pr_warn("failed to find valid kernel BTF\n"); - return libbpf_err_ptr(-ESRCH); + /* return the last error or ESRCH if no fallback locations were found */ + return btf ?: libbpf_err_ptr(-ESRCH); } struct btf *libbpf_find_kernel_btf(void) __attribute__((alias("btf__load_vmlinux_btf"))); -- 2.43.0.429.g432eaa2c6b-goog
