On Mon, Jan 29, 2024 at 4:43 PM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > On Thu, Jan 25, 2024 at 3:18 PM Ian Rogers <irogers@xxxxxxxxxx> wrote: > > > > 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. > > I did some further simplifications and clean ups while applying. > > I dropped an extra faccessat(R_OK) check for /sys/kernel/btf/vmlinux > and instead if F_OK passes, just go ahead and try to parse > /sys/kernel/btf/vmlinux. If we have no access, we should get -EPERM or > -EACCESS (I didn't check which), otherwise we'll either parse or won't > find any BTF, both are errors. If /sys/kernel/btf/vmlinux exists, > there seems to be little point nowadays to try fallback locations, > kernel clearly is modern enough to generate /sys/kernel/btf/vmlinux, > so we just bail out with error. > > Please check the landed commit in bpf-next and let me know if it > doesn't cover your use case properly. It does, thanks Andrii! Ian > > --- > > 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 > >
