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

[Lancelot SIX <lancelot.six@amd.com>]

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 this by consuming the "Not confirmed\r\n$gdb_prompt " output.

While at cleaning up this test, also improve the regex for the return
test:
- Remove the leading ".*" pattern.
- Replace the "$" (end of line marker) with "\$" because it does not
  identify a TCL variable.

Tested on x86_64-gnu-linux, using

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

Change-Id: I42858b13db2cbd623c5c1739de65ad423e0c0938
---
 gdb/testsuite/gdb.dwarf2/calling-convention.exp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gdb/testsuite/gdb.dwarf2/calling-convention.exp b/gdb/testsuite/gdb.dwarf2/calling-convention.exp
index 0a11cb15c68..7ea9ae7c768 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"
     }
 }
 

base-commit: 5321c31bc78379a33f07dc7bef9256d05b942ad7
-- 
2.25.1