strace.c: move argc/nprocs check to the tracing_backend_init routine

It is deemed that for some tracing backends it is possible to run strace
without providing either program to run or PIDs to attach (attaching to
already running GDB server with existing inferiors is an example). Thus,
let's move this check to tracing_backend_init.

* strace.c (tracing_backend_init): Add (!nprocs && !argc) check.
(init): Remove (!nprocs && !argc) check, update error message for (argc
< 0) check.
* tests/options-syntax.test: Update expected output.

2 files changed, 7 insertions, 5 deletions

diff --git a/strace.c b/strace.c
index 5ea2efcb3..ab93dead3 100644
--- a/strace.c
+++ b/strace.c
@@ -1623,6 +1623,9 @@ tracing_backend_init(int argc, char *argv[])
 {
 	os_release = get_os_release();
 
+	if (!nprocs && !argc)
+		error_msg_and_help("must have PROG [ARGS] or -p PID");
+
 	if (followfork)
 		ptrace_setoptions |= PTRACE_O_TRACECLONE |
 				     PTRACE_O_TRACEFORK |
@@ -1831,9 +1834,8 @@ init(int argc, char *argv[])
 	argv += optind;
 	argc -= optind;
 
-	if (argc < 0 || (!nprocs && !argc)) {
-		error_msg_and_help("must have PROG [ARGS] or -p PID");
-	}
+	if (argc < 0)
+		error_msg_and_help("must have command line arguments");
 
 	if (!argc && daemonized_tracer) {
 		error_msg_and_help("PROG [ARGS] must be specified with -D");
diff --git a/tests/options-syntax.test b/tests/options-syntax.test
index 5e43b3ab8..936ed2955 100755
--- a/tests/options-syntax.test
+++ b/tests/options-syntax.test
@@ -76,12 +76,12 @@ esac
 	dump_log_and_fail_with \
 		'zeroargc strace failed to handle the error properly'
 cat > "$EXP" << __EOF__
-$STRACE_EXE: must have PROG [ARGS] or -p PID
+$STRACE_EXE: must have command line arguments
 Try '$STRACE_EXE -h' for more information.
 __EOF__
 diff -u -- "$EXP" "$LOG" > /dev/null || {
 	cat > "$EXP" <<- '__EOF__'
-	strace: must have PROG [ARGS] or -p PID
+	strace: must have command line arguments
 	Try 'strace -h' for more information.
 	__EOF__
 	match_diff "$LOG" "$EXP" \