windows-nat: Report an error if ContinueDebugEvent() fails
authorJon Turney <jon.turney@dronecode.org.uk>
Wed, 15 Apr 2015 20:37:11 +0000 (21:37 +0100)
committerJon Turney <jon.turney@dronecode.org.uk>
Wed, 22 Apr 2015 18:40:11 +0000 (19:40 +0100)
commit68ffc90245e2e51ba5f096f166ae49262d461b5e
tree99077c3e086c70bc6873649b98b8d36dd30bbfcc
parent23942819fca67effa062a9639be5df3fb074b322
windows-nat: Report an error if ContinueDebugEvent() fails

Using the 'catch-signal' test from the testsuite, on x86_64 Cygwin:

    $ ./gdb testsuite/outputs/gdb.base/catch-signal/catch-signal.exe
    [...]
    (gdb) catch signal
    Catchpoint 1 (standard signals)
    (gdb) r
    [...]
    Catchpoint 1 (signal SIGHUP), main () at
    ../../../gdb/testsuite/gdb.base/catch-signal.c:40
    40        raise (SIGHUP);               /* second HUP */
    (gdb) c
    Continuing.
    [hangs]

This is due to a defect in the way Cygwin signals are handled: When
handle_output_debug_string processes a Cygwin signal message, it re-writes
current_event.dwThreadId to reflect the thread that the signal will be delivered
to.

Subsequently, the call to ContinueDebugEvent will fail, because we're trying to
resume the wrong thread.  GDB is then stuck waiting forever for another event
that will never come.

This patch doesn't fix the problem, it just adds appropriate error handling.

Using error() seems appropriate here, if ContinueDebugEvent() fails, the
inferior is in an unknown state and we will probably not be debugging it
anymore.

With this patch applied, resuming the execution of the program now yields:

    $ ./gdb testsuite/outputs/gdb.base/catch-signal/catch-signal.exe
    [...]
    (gdb) catch signal
    Catchpoint 1 (standard signals)
    (gdb) r
    [...]
    Catchpoint 1 (signal SIGHUP), main () at
    ../../../gdb/testsuite/gdb.base/catch-signal.c:40
    40        raise (SIGHUP);               /* second HUP */
    (gdb) c
    Continuing.
    main () at ../../../gdb/testsuite/gdb.base/catch-signal.c:40
    40        raise (SIGHUP);               /* second HUP */
    Failed to resume program execution (ContinueDebugEvent failed, error 87)
    (gdb)

gdb/ChangeLog:

2015-04-22  Jon Turney  <jon.turney@dronecode.org.uk>

* windows-nat.c (windows_continue): Report an error if
ContinueDebugEvent() fails.
gdb/ChangeLog
gdb/windows-nat.c