strerror_r(), used from libbpf-specific libbpf_strerror_r() wrapper is documented to return error in two different ways, depending on glibc version. Take that into account when handling strerror_r()'s own errors, which happens when we pass some non-standard (internal) kernel error to it. Before this patch we'd have "ERROR: strerror_r(524)=22", which is quite confusing. Now for the same situation we'll see a bit less visually scary "unknown error (-524)". At least we won't confuse user with irrelevant EINVAL (22). Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx> --- tools/lib/bpf/str_error.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/tools/lib/bpf/str_error.c b/tools/lib/bpf/str_error.c index 146da01979c7..5e6a1e27ddf9 100644 --- a/tools/lib/bpf/str_error.c +++ b/tools/lib/bpf/str_error.c @@ -2,6 +2,7 @@ #undef _GNU_SOURCE #include <string.h> #include <stdio.h> +#include <errno.h> #include "str_error.h" /* make sure libbpf doesn't use kernel-only integer typedefs */ @@ -15,7 +16,18 @@ char *libbpf_strerror_r(int err, char *dst, int len) { int ret = strerror_r(err < 0 ? -err : err, dst, len); - if (ret) - snprintf(dst, len, "ERROR: strerror_r(%d)=%d", err, ret); + /* on glibc <2.13, ret == -1 and errno is set, if strerror_r() can't + * handle the error, on glibc >=2.13 *positive* (errno-like) error + * code is returned directly + */ + if (ret == -1) + ret = errno; + if (ret) { + if (ret == EINVAL) + /* strerror_r() doesn't recognize this specific error */ + snprintf(dst, len, "unknown error (%d)", err < 0 ? err : -err); + else + snprintf(dst, len, "ERROR: strerror_r(%d)=%d", err, ret); + } return dst; } -- 2.43.0