[binutils-gdb] Windows gdb: Avoid hang second attach/run

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=7a15a5f571da8772765bfb17d1049a097205035e

commit 7a15a5f571da8772765bfb17d1049a097205035e
Author: Pedro Alves <[email protected]>
Date:   Fri Jun 2 23:08:49 2023 +0100

    Windows gdb: Avoid hang second attach/run
    
    gdb.base/attach.exp starts a second inferior and tries to attach the
    second inferior to the same process that inferior 1 is already
    debugging.  The point is to make sure that the backend errors out when
    it tries to attach to a process that is already being debugged.
    
    windows_nat_target::attach and windows_nat_target::create_inferior
    both hang in this situation, because they call into do_synchronously,
    which hangs because the 'process_thread' thread is blocked in
    WaitForDebugEvent.
    
    E.g.:
    
      attach 4420
      FAIL: gdb.base/attach.exp: do_attach_failure_tests: fail to attach again (timeout)
    
    Until the Windows backend is taught to debug multiple processes, which
    will probably require having one process_thread thread per inferior,
    detect the situation and error out before GDB hangs.
    
    This results in the following progression in gdb.base/attach.exp:
    
     -FAIL: gdb.base/attach.exp: do_attach_failure_tests: fail to attach again (timeout)
     -FAIL: gdb.base/attach.exp: do_attach_failure_tests: set confirm off (timeout)
     -FAIL: gdb.base/attach.exp: do_attach_failure_tests: switch to inferior 1 (timeout)
     -FAIL: gdb.base/attach.exp: do_attach_failure_tests: exit after attach failures (timeout)
     -FAIL: gdb.base/attach.exp: do_attach_failure_tests: gdb_breakpoint: set breakpoint at main (timeout)
     -FAIL: gdb.base/attach.exp: do_attach_failure_tests: stop at main (timeout)
     +PASS: gdb.base/attach.exp: do_attach_failure_tests: fail to attach again
     +PASS: gdb.base/attach.exp: do_attach_failure_tests: set confirm off
     +PASS: gdb.base/attach.exp: do_attach_failure_tests: switch to inferior 1
     +PASS: gdb.base/attach.exp: do_attach_failure_tests: exit after attach failures
     +PASS: gdb.base/attach.exp: do_attach_failure_tests: stop at main
    
    There are still other failures not addressed by this patch.
    
    Tests that launch a second program with "run" exist, but are normally
    gated by allow_multi_inferior_tests.
    
    Approved-By: Tom Tromey <[email protected]>
    Change-Id: I55b4438795439673c49fa55f55ddf0191f4f0ea8
    commit-id: 1caa5be0

Diff:
---
 gdb/testsuite/gdb.base/attach.exp |  4 ++++
 gdb/windows-nat.c                 | 19 +++++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/gdb/testsuite/gdb.base/attach.exp b/gdb/testsuite/gdb.base/attach.exp
index bffdfd9b1aa..a4e7d72ef94 100644
--- a/gdb/testsuite/gdb.base/attach.exp
+++ b/gdb/testsuite/gdb.base/attach.exp
@@ -175,6 +175,10 @@ proc_with_prefix do_attach_failure_tests {} {
 	    # Response expected when using gdbserver.
 	    pass "$test"
 	}
+	-re -wrap "Can only debug one process at a time\\." {
+	    # Response expected on Windows.
+	    pass "$test"
+	}
     }
 
     # To ensure the target is still alive and working after this, try to run
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index b9d32b6c0c4..d506b42fbda 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -2056,14 +2056,24 @@ out:
   return ret;
 }
 
+/* Throw an error if we're already debugging a Windows process.  We
+   can only debug one at a time currently.  */
+
+static void
+ensure_only_one_process ()
+{
+  if (windows_process->process_id != 0)
+    error (_("Can only debug one process at a time."));
+}
+
 /* Attach to process PID, then initialize for debugging it.  */
 
 void
 windows_nat_target::attach (const char *args, int from_tty)
 {
-  DWORD pid;
+  ensure_only_one_process ();
 
-  pid = parse_pid_to_attach (args);
+  DWORD pid = parse_pid_to_attach (args);
 
   if (set_process_privilege (SE_DEBUG_NAME, TRUE) < 0)
     warning ("Failed to get SE_DEBUG_NAME privilege\n"
@@ -2415,6 +2425,8 @@ windows_nat_target::detach (inferior *inf, int from_tty)
   switch_to_no_thread ();
   detach_inferior (inf);
 
+  windows_process->process_id = 0;
+
   maybe_unpush_target ();
 }
 
@@ -2857,6 +2869,8 @@ windows_nat_target::create_inferior (const char *exec_file,
   DWORD flags = 0;
   const std::string &inferior_tty = current_inferior ()->tty ();
 
+  ensure_only_one_process ();
+
   if (!exec_file)
     error (_("No executable specified, use `target exec'."));
 
@@ -3166,6 +3180,7 @@ windows_nat_target::mourn_inferior ()
       CHECK (CloseHandle (windows_process->handle));
       windows_process->open_process_used = 0;
     }
+  windows_process->process_id = 0;
   inf_child_target::mourn_inferior ();
 }