Fix gdb.base/starti.exp racy test

This commit fixes a couple problems with gdb.base/starti.exp, causing
spurious FAILs.

The first is a double-prompt problem:

~~~
 (gdb) PASS: gdb.base/starti.exp: hook-stop
 starti
 [....]
 gdb_expect_list pattern: /\$1 = 0/
 $1 = 0

 gdb_expect_list pattern: //
 0x00007ffff7ddcc80 in _start () from /lib64/ld-linux-x86-64.so.2

 (gdb)                                         # EXPECTED PROMPT
 (gdb) PASS: gdb.base/starti.exp: starti       # ANOTHER PROMPT!
 break main
~~~

This happens because the test uses gdb_test_sequence with no command,
like this:

 gdb_test_sequence "" "starti" {
     "Program stopped."
     "\\$1 = 0"
 }

but gdb_test_sequence doesn't have a check for empty command like
gdb_test_multiple does, and so sends "\n" to GDB:

 proc gdb_test_sequence { command test_name expected_output_list } {
     global gdb_prompt
     if { $test_name == "" } {
	 set test_name $command
     }
     lappend expected_output_list ""; # implicit ".*" before gdb prompt
     send_gdb "$command\n"
     return [gdb_expect_list $test_name "$gdb_prompt $" $expected_output_list]
 }

"starti" is a no-repeat command, so pressing <ret> just makes another
prompt appear, confusing the following gdb_test/gdb_test_multiple/etc.

Even with that fixed, the testcase is still racy though.

The second problem is that sometimes the "continue" test times out
here:

~~~
 continue
 Continuing.
 $2 = 1


 gdb_expect_list pattern: /.*Breakpoint .*main \(\) at .*starti.c.*/
 Breakpoint 1, main () at /home/pedro/src/gdb/testsuite/gdb.base/starti.c:29
 29	  return 0;
 (gdb) gdb_expect_list pattern: //
 * hung here *
~~~

The problem is that the too-greedy ".*" trailing match in
gdb_expect_list's pattern ends up consuming GDB's prompt too soon.
Fix that by removing the unnecessary trailing ".*".  While at it,
remove all ".*"s to be stricter.

Tested on x86_64 GNU/Linux.

gdb/testsuite/ChangeLog:
2017-11-16  Pedro Alves  <palves@redhat.com>

	* gdb.base/starti.exp ("continue" test): Remove ".*"s from
	pattern.
	* lib/gdb.exp (gdb_test_sequence): Don't send empty command to
	GDB.

3 files changed, 13 insertions, 3 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index bb8dd79..547a3be 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2017-11-16  Pedro Alves  <palves@redhat.com>
+
+	* gdb.base/starti.exp ("continue" test): Remove ".*"s from
+	pattern.
+	* lib/gdb.exp (gdb_test_sequence): Don't send empty command to
+	GDB.
+
 2017-11-15  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* gdb.tui/completionn.exp (test_tab_completion): Add space in
diff --git a/gdb/testsuite/gdb.base/starti.exp b/gdb/testsuite/gdb.base/starti.exp
index 98167ce..76e68d5 100644
--- a/gdb/testsuite/gdb.base/starti.exp
+++ b/gdb/testsuite/gdb.base/starti.exp
@@ -47,5 +47,5 @@ gdb_test_sequence "" "starti" {
 gdb_breakpoint main
 gdb_test_sequence "continue" "" {
     "\\$2 = 1"
-    ".*Breakpoint .*main \\(\\) at .*starti.c.*"
+    "Breakpoint \[^\r\n\]*main \\(\\) at \[^\r\n\]*starti.c"
 }
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 548cb06..8d6972a 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -1093,7 +1093,8 @@ proc gdb_test_no_output { args } {
 # This is useful when the sequence is long and contains ".*", a single
 # regexp to match the entire output can get a timeout much easier.
 #
-# COMMAND is the command to send.
+# COMMAND is the command to execute, send to GDB with send_gdb.  If
+#   this is the null string no command is sent.
 # TEST_NAME is passed to pass/fail.  COMMAND is used if TEST_NAME is "".
 # EXPECTED_OUTPUT_LIST is a list of regexps of expected output, which are
 # processed in order, and all must be present in the output.
@@ -1116,7 +1117,9 @@ proc gdb_test_sequence { command test_name expected_output_list } {
 	set test_name $command
     }
     lappend expected_output_list ""; # implicit ".*" before gdb prompt
-    send_gdb "$command\n"
+    if { $command != "" } {
+	send_gdb "$command\n"
+    }
     return [gdb_expect_list $test_name "$gdb_prompt $" $expected_output_list]
 }