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 libbpf: failed to load object 'lock_contention_bpf' libbpf: failed to load BPF skeleton 'lock_contention_bpf': -3 ``` After no access /sys/kernel/btf/vmlinux: ``` libbpf: Unable to access canonical vmlinux BTF from /sys/kernel/btf/vmlinux libbpf: Error loading vmlinux BTF: -3 libbpf: failed to load object 'lock_contention_bpf' libbpf: failed to load BPF skeleton 'lock_contention_bpf': -3 ``` After no BTF /sys/kernel/btf/vmlinux: ``` libbpf: Failed to load vmlinux BTF from /sys/kernel/btf/vmlinux, was CONFIG_DEBUG_INFO_BTF enabled? libbpf: Error loading vmlinux BTF: -3 libbpf: failed to load object 'lock_contention_bpf' libbpf: failed to load BPF skeleton 'lock_contention_bpf': -3 ``` Closes: https://lore.kernel.org/bpf/CAP-5=fU+DN_+Y=Y4gtELUsJxKNDDCOvJzPHvjUVaUoeFAzNnig@xxxxxxxxxxxxxx/ Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx> --- v2. Try to address review comments from Andrii Nakryiko. --- tools/lib/bpf/btf.c | 49 ++++++++++++++++++++++++++++++++------------- 1 file changed, 35 insertions(+), 14 deletions(-) diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index ee95fd379d4d..d8a05dda0836 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c @@ -4920,16 +4920,25 @@ static int btf_dedup_remap_types(struct btf_dedup *d) return 0; } +static struct btf *btf__load_vmlinux_btf_path(const char *path) +{ + struct btf *btf; + int err; + + btf = btf__parse(path, NULL); + err = libbpf_get_error(btf); + pr_debug("loading kernel BTF '%s': %d\n", path, err); + return err ? NULL : btf; +} + /* * Probe few well-known locations for vmlinux kernel image and try to load BTF * data out of it to use for target BTF. */ struct btf *btf__load_vmlinux_btf(void) { + /* 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", @@ -4938,29 +4947,41 @@ struct btf *btf__load_vmlinux_btf(void) "/usr/lib/debug/boot/vmlinux-%1$s.debug", "/usr/lib/debug/lib/modules/%1$s/vmlinux", }; - char path[PATH_MAX + 1]; + const char *location; struct utsname buf; struct btf *btf; - int i, err; + int i; - uname(&buf); + /* try canonical vmlinux BTF through sysfs first */ + location = "/sys/kernel/btf/vmlinux"; + if (faccessat(AT_FDCWD, location, R_OK, AT_EACCESS) == 0) { + btf = btf__load_vmlinux_btf_path(location); + if (btf) + return btf; + + pr_warn("Failed to load vmlinux BTF from %s, was CONFIG_DEBUG_INFO_BTF enabled?\n", + location); + } else + pr_warn("Unable to access canonical vmlinux BTF from %s\n", location); + uname(&buf); for (i = 0; i < ARRAY_SIZE(locations); i++) { - snprintf(path, PATH_MAX, locations[i], buf.release); + char path[PATH_MAX + 1]; + + snprintf(path, sizeof(path), locations[i], buf.release); + btf = btf__load_vmlinux_btf_path(path); if (faccessat(AT_FDCWD, path, R_OK, AT_EACCESS)) continue; - btf = btf__parse(path, NULL); - err = libbpf_get_error(btf); - pr_debug("loading kernel BTF '%s': %d\n", path, err); - if (err) - continue; + btf = btf__load_vmlinux_btf_path(location); + if (btf) + return btf; - return btf; + pr_warn("Failed to load vmlinux BTF from %s, was CONFIG_DEBUG_INFO_BTF enabled?\n", + path); } - pr_warn("failed to find valid kernel BTF\n"); return libbpf_err_ptr(-ESRCH); } -- 2.43.0.429.g432eaa2c6b-goog
