gdb/testsuite: Fix race in gdb.dwarf2/calling-convention.exp

Pedro Alves warned me that there is a race in
gdb.dwarf2/calling-convention.exp making the test sometimes fail on his
setup.  This can be reliably reproduced using :

    make check-read1 TESTS="gdb.dwarf2/calling-convention.exp"

The relevant part of the gdb.log file is:

    return 35
    Function 'foo' does not follow the target calling convention.
    If you continue, setting the return value will probably lead to unpredictable behaviors.
    Make foo return now? (y or n) PASS: gdb.dwarf2/calling-convention.exp: return 35
    n
    Not confirmed
    (gdb) FAIL: gdb.dwarf2/calling-convention.exp: finish

The issue is that when doing the test for "return 35", the DejaGnu test
sends "n" (to tell GDB not to perform the return action) but never
consumes the "Not confirmed" acknowledgment sent by GDB.  Later, when
trying to do the next test, DejaGnu tries to match the leftover output
from the "return" test. As this output is not expected, the test fails.

Fix by using gdb_test to send the "n" answer and match the confirmation
and consume all output to the prompt.

Also do minor adjustments to the main regex:
  - Remove the leading ".*" which is not required.
  - Ensure that the "?" from the question is properly escaped.

Tested on x86_64-gnu-linux, using

- make check TESTS="gdb.dwarf2/calling-convention.exp"
- make check-read1 TESTS="gdb.dwarf2/calling-convention.exp"
- make check-readmore TESTS="gdb.dwarf2/calling-convention.exp"

Co-authored-by: Pedro Alves <pedro@palves.net>
Change-Id: I42858b13db2cbd623c5c1739de65ad423e0c0938

1 files changed, 2 insertions, 2 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/calling-convention.exp b/gdb/testsuite/gdb.dwarf2/calling-convention.exp
index 0a11cb15c6..77107a4235 100644
--- a/gdb/testsuite/gdb.dwarf2/calling-convention.exp
+++ b/gdb/testsuite/gdb.dwarf2/calling-convention.exp
@@ -84,9 +84,9 @@ gdb_breakpoint "foo"
 gdb_continue_to_breakpoint "foo"
 
 gdb_test_multiple "return 35" "" {
-    -re ".*Function 'foo' does not follow the target calling convention.\r\nIf you continue, setting the return value will probably lead to unpredictable behaviors.\r\nMake foo return now?.*\\(y or n\\) $" {
-	send_gdb "n\n"
+    -re "Function 'foo' does not follow the target calling convention.\r\nIf you continue, setting the return value will probably lead to unpredictable behaviors.\r\nMake foo return now\\? \\(y or n\\) $" {
 	pass $gdb_test_name
+	gdb_test "n" "Not confirmed" "cancel return"
     }
 }