libbpf: Return non-null error on failures in libbpf_find_prog_btf_id()

Variable "err" is initialised to -EINVAL so that this error code is
returned when something goes wrong in libbpf_find_prog_btf_id().
However, a recent change in the function made use of the variable in
such a way that it is set to 0 if retrieving linear information on the
program is successful, and this 0 value remains if we error out on
failures at later stages.

Let's fix this by setting err to -EINVAL later in the function.

Fixes: e9fc3ce99b34 ("libbpf: Streamline error reporting for high-level APIs")
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210729162028.29512-2-quentin@isovalent.com

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a1ca6fb..7b2b5d2 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8317,7 +8317,7 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
        struct bpf_prog_info_linear *info_linear;
        struct bpf_prog_info *info;
        struct btf *btf = NULL;
-       int err = -EINVAL;
+       int err;
 
        info_linear = bpf_program__get_prog_info_linear(attach_prog_fd, 0);
        err = libbpf_get_error(info_linear);
@@ -8326,6 +8326,8 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
                        attach_prog_fd);
                return err;
        }
+
+       err = -EINVAL;
        info = &info_linear->info;
        if (!info->btf_id) {
                pr_warn("The target program doesn't have BTF\n");