tracing/probes: Point the error offset correctly for eprobe argument error

Fix to point the error offset correctly for eprobe argument error.
In the cleanup commit 1b8b0cd ("tracing/probes: Move event parameter
fetching code to common parser"), due to incorrect backward compatibility
aimed at conforming to the test specifications, the error location was set
to 0 when a non-existent formal parameter was specified for Eprobe.
However, this should be corrected in both the test and the implementation
to point correct error position.

Link: https://lore.kernel.org/all/177967567399.209006.1451571244515632097.stgit@devnote2/

Fixes: 1b8b0cd ("tracing/probes: Move event parameter fetching code to common parser")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

Author: mhiramat

kernel/trace/trace_probe.c

@@ -962,8 +962,6 @@ static int parse_probe_vars(char *orig_arg, const struct fetch_type *t,
 			code->op = FETCH_OP_COMM;
 			return 0;
 		}
-		/* backward compatibility */
-		ctx->offset = 0;
 		goto inval;
 	}
 

tools/testing/selftests/ftrace/test.d/dynevent/eprobes_syntax_errors.tc

@@ -20,7 +20,7 @@ check_error 'e:foo/^123456789012345678901234567890123456789012345678901234567890
 check_error 'e:foo/^bar.1 syscalls/sys_enter_openat'	# BAD_EVENT_NAME
 
 check_error 'e:foo/bar syscalls/sys_enter_openat arg=^dfd'	# BAD_FETCH_ARG
-check_error 'e:foo/bar syscalls/sys_enter_openat ^arg=$foo'	# BAD_ATTACH_ARG
+check_error 'e:foo/bar syscalls/sys_enter_openat arg=^$foo'	# BAD_ATTACH_ARG
 
 if grep -q '<attached-group>\.<attached-event>.*\[if <filter>\]' README; then
   check_error 'e:foo/bar syscalls/sys_enter_openat if ^'	# NO_EP_FILTER