selftests/bpf: Print reason when a tester could not run a program

Commit 8184d44 ("selftests/bpf: skip verifier tests for unsupported program types") added a check to skip unsupported program types. As bpf_probe_prog_type can change errno, do_single_test should save it before printing a reason why a supported BPF program type failed to load. Fixes: 8184d44 ("selftests/bpf: skip verifier tests for unsupported program types") Cc: Stanislav Fomichev <sdf@google.com> Cc: Krzesimir Nowak <krzesimir@kinvolk.io> Signed-off-by: Florian Lehner <dev@der-flo.net> Acked-by: Andrii Nakryiko <andrii@kernel.org>

Author: florianl

tools/testing/selftests/bpf/test_verifier.c

@@ -936,6 +936,7 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
 int run_errs, run_successes;
 int map_fds[MAX_NR_MAPS];
 const char *expected_err;
+int saved_errno;
 int fixup_skips;
 __u32 pflags;
 int i, err;
@@ -997,6 +998,7 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
 }
 
 fd_prog = bpf_load_program_xattr(&attr, bpf_vlog, sizeof(bpf_vlog));
+saved_errno = errno;
 
 /* BPF_PROG_TYPE_TRACING requires more setup and
  * bpf_probe_prog_type won't give correct answer
@@ -1013,7 +1015,7 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
 if (expected_ret == ACCEPT || expected_ret == VERBOSE_ACCEPT) {
 if (fd_prog < 0) {
 printf("FAIL\nFailed to load prog '%s'!\n",
- strerror(errno));
+ strerror(saved_errno));
 goto fail_log;
 }
 #ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS