Fix paginate-*.exp races

Jan pointed out in
<https://sourceware.org/ml/gdb-patches/2014-07/msg00553.html> that
these testcases have racy results:

  gdb.base/double-prompt-target-event-error.exp
  gdb.base/paginate-after-ctrl-c-running.exp
  gdb.base/paginate-bg-execution.exp
  gdb.base/paginate-execution-startup.exp
  gdb.base/paginate-inferior-exit.exp

This is easily reproducible with "read1" from:

  [reproducer for races of expect incomplete reads]
  http://sourceware.org/bugzilla/show_bug.cgi?id=12649

The '-notransfer -re "<return>" { exp_continue }' trick in the current
tests doesn't actually work.

The issue that led to the -notransfer trick was that

  "---Type <return> to continue, or q <return> to quit---"

has two "<return>"s.  If one wants gdb_test_multiple to not hit the
built-in "<return>" match that results in FAIL, one has to expect the
pagination prompt in chunks, first up to the first "<return>", then
again, up to the second.  Something around these lines:

  gdb_test_multiple "" $test {
      -re "<return>" {
	  exp_continue
      }
      -re "to quit ---" {
	  pass $test
      }
  }

The intent was for -notransfer+exp_continue to make expect fetch more
input, and rerun the matches against the now potentially fuller
buffer, and then eventually the -re that includes the full pagination
prompt regex would match instead (because it's listed higher up, it
would match first).  But, once that "<return>" -notransfer -re
matches, it keeps re-matching forever.  It seems like with
exp_continue, expect immediately retries matching, instead of first
reading in more data into the buffer, if available.

Fix this like I should have done in the first place.  There's actually
no good reason for gdb_test_multiple to only match "<return>".  We can
make gdb_test_multiple expect the whole pagination prompt text
instead, which is store in the 'pagination_prompt' global (similar to
'gdb_prompt').  Then a gdb_test_multiple caller that doesn't want the
default match to trigger, because it wants to see one pagination
prompt, does simply:

  gdb_test_multiple "" $test {
      -re "$pagination_prompt$" {
	  pass $test
      }
  }

which is just like when we don't want the default $gdb_prompt match
within gdb_test_multiple to trigger, like:

  gdb_test_multiple "" $test {
      -re "$gdb_prompt $" {
	  pass $test
      }
  }

Tested on x86_64 Fedora 20.  In addition, I've let the racy tests run
all in parallel in a loop for 30 minutes, and they never failed.

gdb/testsuite/
2014-07-25  Pedro Alves  <palves@redhat.com>

	* gdb.base/double-prompt-target-event-error.exp
	(cancel_pagination_in_target_event): Remove '-notransfer <return>'
	match.
	(cancel_pagination_in_target_event): Rework double prompt
	detection.
	* gdb.base/paginate-after-ctrl-c-running.exp
	(test_ctrlc_while_target_running_paginates): Remove '-notransfer
	<return>' match.
	* gdb.base/paginate-bg-execution.exp
	(test_bg_execution_pagination_return)
	(test_bg_execution_pagination_cancel): Remove '-notransfer
	<return>' matches.
	* gdb.base/paginate-execution-startup.exp
	(test_fg_execution_pagination_return)
	(test_fg_execution_pagination_cancel): Remove '-notransfer
	<return>' matches.
	* gdb.base/paginate-inferior-exit.exp
	(test_paginate_inferior_exited): Remove '-notransfer <return>'
	match.
	* lib/gdb-utils.exp (string_to_regexp): Move here from lib/gdb.exp.
	* lib/gdb.exp (pagination_prompt): Run text through
	string_to_regexp.
	(gdb_test_multiple): Match $pagination_prompt instead of
	"<return>".
	(string_to_regexp): Move to lib/gdb-utils.exp.

8 files changed, 56 insertions, 46 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index f534f18..bd8cf44 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,31 @@
+2014-07-25  Pedro Alves  <palves@redhat.com>
+
+	* gdb.base/double-prompt-target-event-error.exp
+	(cancel_pagination_in_target_event): Remove '-notransfer <return>'
+	match.
+	(cancel_pagination_in_target_event): Rework double prompt
+	detection.
+	* gdb.base/paginate-after-ctrl-c-running.exp
+	(test_ctrlc_while_target_running_paginates): Remove '-notransfer
+	<return>' match.
+	* gdb.base/paginate-bg-execution.exp
+	(test_bg_execution_pagination_return)
+	(test_bg_execution_pagination_cancel): Remove '-notransfer
+	<return>' matches.
+	* gdb.base/paginate-execution-startup.exp
+	(test_fg_execution_pagination_return)
+	(test_fg_execution_pagination_cancel): Remove '-notransfer
+	<return>' matches.
+	* gdb.base/paginate-inferior-exit.exp
+	(test_paginate_inferior_exited): Remove '-notransfer <return>'
+	match.
+	* lib/gdb-utils.exp (string_to_regexp): Move here from lib/gdb.exp.
+	* lib/gdb.exp (pagination_prompt): Run text through
+	string_to_regexp.
+	(gdb_test_multiple): Match $pagination_prompt instead of
+	"<return>".
+	(string_to_regexp): Move to lib/gdb-utils.exp.
+
 2014-07-22  Jan Kratochvil  <jan.kratochvil@redhat.com>
 
 	* gdb.arch/amd64-entry-value-paramref.S: New file.
diff --git a/gdb/testsuite/gdb.base/double-prompt-target-event-error.exp b/gdb/testsuite/gdb.base/double-prompt-target-event-error.exp
index 5571cdf..84c6c45 100644
--- a/gdb/testsuite/gdb.base/double-prompt-target-event-error.exp
+++ b/gdb/testsuite/gdb.base/double-prompt-target-event-error.exp
@@ -75,10 +75,6 @@ proc cancel_pagination_in_target_event { command } {
 		set saw_continuing 1
 		exp_continue
 	    }
-	    -notransfer -re "<return>" {
-		# Otherwise gdb_test_multiple considers this an error.
-		exp_continue
-	    }
 	}
 
 	# We're now stopped in a pagination query while handling a
@@ -87,18 +83,28 @@ proc cancel_pagination_in_target_event { command } {
 	# output.
 	send_gdb "\003p 1\n"
 
+	# Note gdb_test_multiple has a default match for the prompt,
+	# which issues a FAIL.  Consume the first prompt.
+	set test "first prompt"
+	gdb_test_multiple "" $test {
+	    -re "$gdb_prompt" {
+		pass "first prompt"
+	    }
+	}
+
+	# We should only see one prompt more, and it should be
+	# preceeded by print's output.
 	set test "no double prompt"
 	gdb_test_multiple "" $test {
-	    -re "$gdb_prompt.*$gdb_prompt.*$gdb_prompt $" {
+	    -re "$gdb_prompt.*$gdb_prompt $" {
+		# The bug is present, and expect managed to read
+		# enough characters into the buffer to fill it with
+		# both prompts.
 		fail $test
 	    }
-	    -re "$gdb_prompt .* = 1\r\n$gdb_prompt $" {
+	    -re " = 1\r\n$gdb_prompt $" {
 		pass $test
 	    }
-	    -notransfer -re "<return>" {
-		# Otherwise gdb_test_multiple considers this an error.
-		exp_continue
-	    }
 	}
 
 	# In case the board file wants to send further commands.
diff --git a/gdb/testsuite/gdb.base/paginate-after-ctrl-c-running.exp b/gdb/testsuite/gdb.base/paginate-after-ctrl-c-running.exp
index 0ed8c92..5898d5b 100644
--- a/gdb/testsuite/gdb.base/paginate-after-ctrl-c-running.exp
+++ b/gdb/testsuite/gdb.base/paginate-after-ctrl-c-running.exp
@@ -70,10 +70,6 @@ proc test_ctrlc_while_target_running_paginates {} {
 	    -re "$gdb_prompt $" {
 		gdb_assert $saw_pagination_prompt $test
 	    }
-	    -notransfer -re "<return>" {
-		# Otherwise gdb_test_multiple considers this an error.
-		exp_continue
-	    }
 	}
 
 	# Confirm GDB can still process input.
diff --git a/gdb/testsuite/gdb.base/paginate-bg-execution.exp b/gdb/testsuite/gdb.base/paginate-bg-execution.exp
index dcff8ad..116cc2b 100644
--- a/gdb/testsuite/gdb.base/paginate-bg-execution.exp
+++ b/gdb/testsuite/gdb.base/paginate-bg-execution.exp
@@ -51,11 +51,6 @@ proc test_bg_execution_pagination_return {} {
 		send_gdb "\n"
 		exp_continue
 	    }
-	    -notransfer -re "<return>" {
-		# Otherwise gdb_test_multiple considers this an
-		# error.
-		exp_continue
-	    }
 	    -re "after sleep\[^\r\n\]+\r\n$" {
 		gdb_assert $saw_pagination_prompt $test
 	    }
@@ -96,10 +91,6 @@ proc test_bg_execution_pagination_cancel { how } {
 	    -re "$pagination_prompt$" {
 		pass $test
 	    }
-	    -notransfer -re "<return>" {
-		# Otherwise gdb_test_multiple considers this an error.
-		exp_continue
-	    }
 	}
 
 	set test "cancel pagination"
diff --git a/gdb/testsuite/gdb.base/paginate-execution-startup.exp b/gdb/testsuite/gdb.base/paginate-execution-startup.exp
index dc713ec..1628a0f 100644
--- a/gdb/testsuite/gdb.base/paginate-execution-startup.exp
+++ b/gdb/testsuite/gdb.base/paginate-execution-startup.exp
@@ -111,10 +111,6 @@ proc test_fg_execution_pagination_return {} {
 		send_gdb "\n"
 		exp_continue
 	    }
-	    -notransfer -re "<return>" {
-		# Otherwise gdb_test_multiple considers this an error.
-		exp_continue
-	    }
 	    -re "$gdb_prompt $" {
 		gdb_assert $saw_pagination_prompt $test
 	    }
@@ -154,10 +150,6 @@ proc test_fg_execution_pagination_cancel { how } {
 	    -re "$pagination_prompt$" {
 		pass $test
 	    }
-	    -notransfer -re "<return>" {
-		# Otherwise gdb_test_multiple considers this an error.
-		exp_continue
-	    }
 	}
 
 	set test "cancel pagination"
diff --git a/gdb/testsuite/gdb.base/paginate-inferior-exit.exp b/gdb/testsuite/gdb.base/paginate-inferior-exit.exp
index 0e37be9..7c63289 100644
--- a/gdb/testsuite/gdb.base/paginate-inferior-exit.exp
+++ b/gdb/testsuite/gdb.base/paginate-inferior-exit.exp
@@ -58,10 +58,6 @@ proc test_paginate_inferior_exited {} {
 		set saw_starting 1
 		exp_continue
 	    }
-	    -notransfer -re "<return>" {
-		# Otherwise gdb_test_multiple considers this an error.
-		exp_continue
-	    }
 	}
 
 	# We're now stopped in a pagination output while handling a
diff --git a/gdb/testsuite/lib/gdb-utils.exp b/gdb/testsuite/lib/gdb-utils.exp
index 7e03cbf..0af437e 100644
--- a/gdb/testsuite/lib/gdb-utils.exp
+++ b/gdb/testsuite/lib/gdb-utils.exp
@@ -28,3 +28,12 @@ proc gdb_init_commands {} {
     }
     return $commands
 }
+
+# Given an input string, adds backslashes as needed to create a
+# regexp that will match the string.
+
+proc string_to_regexp {str} {
+    set result $str
+    regsub -all {[]*+.|()^$\[\\]} $str {\\&} result
+    return $result
+}
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 7a00efb..8cb98ae 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -71,7 +71,7 @@ if ![info exists gdb_prompt] then {
 }
 
 # A regexp that matches the pagination prompt.
-set pagination_prompt "---Type <return> to continue, or q <return> to quit---"
+set pagination_prompt [string_to_regexp "---Type <return> to continue, or q <return> to quit---"]
 
 # The variable fullname_syntax_POSIX is a regexp which matches a POSIX 
 # absolute path ie. /foo/ 
@@ -649,7 +649,7 @@ proc gdb_internal_error_resync {} {
 #
 proc gdb_test_multiple { command message user_code } {
     global verbose use_gdb_stub
-    global gdb_prompt
+    global gdb_prompt pagination_prompt
     global GDB
     global inferior_exited_re
     upvar timeout timeout
@@ -873,7 +873,7 @@ proc gdb_test_multiple { command message user_code } {
 	    }
 	    set result 1
 	}
-	"<return>" {
+	-re "$pagination_prompt" {
 	    send_gdb "\n"
 	    perror "Window too small."
 	    fail "$message"
@@ -1109,14 +1109,6 @@ proc test_print_reject { args } {
     }
 }
 
-# Given an input string, adds backslashes as needed to create a
-# regexp that will match the string.
-
-proc string_to_regexp {str} {
-    set result $str
-    regsub -all {[]*+.|()^$\[\\]} $str {\\&} result
-    return $result
-}
 
 # Same as gdb_test, but the second parameter is not a regexp,
 # but a string that must match exactly.