libbpf: Prevent overriding errno when logging errors

Turns out there were a few more instances where libbpf didn't save the
errno before writing an error message, causing errno to be overridden by
the printf() return and the error disappearing if logging is enabled.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200813142905.160381-1-toke@redhat.com

tools/lib/bpf/libbpf.c

@@ -3478,10 +3478,11 @@ bpf_object__probe_global_data(struct bpf_object *obj)
 
 	map = bpf_create_map_xattr(&map_attr);
 	if (map < 0) {
-		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
+		ret = -errno;
+		cp = libbpf_strerror_r(ret, errmsg, sizeof(errmsg));
 		pr_warn("Error in %s():%s(%d). Couldn't create simple array map.\n",
-			__func__, cp, errno);
-		return -errno;
+			__func__, cp, -ret);
+		return ret;
 	}
 
 	insns[0].imm = map;
@@ -6012,9 +6013,10 @@ int bpf_program__pin_instance(struct bpf_program *prog, const char *path,
 	}
 
 	if (bpf_obj_pin(prog->instances.fds[instance], path)) {
-		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
+		err = -errno;
+		cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
 		pr_warn("failed to pin program: %s\n", cp);
-		return -errno;
+		return err;
 	}
 	pr_debug("pinned program '%s'\n", path);