[PATCH] Cygwin: pty: Use pinfo() rather than kill() with signal 0.

[Takashi Yano <takashi dot yano at nifty dot ne dot jp>]

- PTY code has a problem that tcsh is terminated if the following
  command is executed.
    true; chcp &
  This seems to be caused by invalid pointer access which occurs
  when the process exits during the kill() code is execuetd. This
  patch avoids the issue by not using kill().
---
 winsup/cygwin/fhandler.h      |  2 +-
 winsup/cygwin/fhandler_tty.cc | 10 +++++-----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/winsup/cygwin/fhandler.h b/winsup/cygwin/fhandler.h
index 9270c837c..82527eca3 100644
--- a/winsup/cygwin/fhandler.h
+++ b/winsup/cygwin/fhandler.h
@@ -2211,7 +2211,7 @@ class fhandler_pty_slave: public fhandler_pty_common
   {
     if (!mask && get_ttyp ()->pcon_pid &&
 	get_ttyp ()->pcon_pid != myself->pid &&
-	kill (get_ttyp ()->pcon_pid, 0) == 0)
+	!!pinfo (get_ttyp ()->pcon_pid))
       return;
     get_ttyp ()->mask_switch_to_pcon_in = mask;
   }
diff --git a/winsup/cygwin/fhandler_tty.cc b/winsup/cygwin/fhandler_tty.cc
index 1dd57b369..181bed5a9 100644
--- a/winsup/cygwin/fhandler_tty.cc
+++ b/winsup/cygwin/fhandler_tty.cc
@@ -1103,7 +1103,7 @@ fhandler_pty_slave::set_switch_to_pcon (int fd_set)
 skip_console_setting:
       restore_reattach_pcon ();
       if (get_ttyp ()->pcon_pid == 0 ||
-	  kill (get_ttyp ()->pcon_pid, 0) != 0)
+	  !pinfo (get_ttyp ()->pcon_pid))
 	get_ttyp ()->pcon_pid = myself->pid;
       get_ttyp ()->switch_to_pcon_in = true;
     }
@@ -1111,7 +1111,7 @@ skip_console_setting:
     {
       wait_pcon_fwd ();
       if (get_ttyp ()->pcon_pid == 0 ||
-	  kill (get_ttyp ()->pcon_pid, 0) != 0)
+	  !pinfo (get_ttyp ()->pcon_pid))
 	get_ttyp ()->pcon_pid = myself->pid;
       get_ttyp ()->switch_to_pcon_out = true;
     }
@@ -1124,7 +1124,7 @@ fhandler_pty_slave::reset_switch_to_pcon (void)
     this->set_switch_to_pcon (fd);
   if (get_ttyp ()->pcon_pid &&
       get_ttyp ()->pcon_pid != myself->pid &&
-      kill (get_ttyp ()->pcon_pid, 0) == 0)
+      !!pinfo (get_ttyp ()->pcon_pid))
     /* There is a process which is grabbing pseudo console. */
     return;
   if (isHybrid)
@@ -2728,7 +2728,7 @@ fhandler_pty_slave::fixup_after_attach (bool native_maybe, int fd_set)
 		ENABLE_PROCESSED_INPUT | ENABLE_LINE_INPUT | ENABLE_ECHO_INPUT;
 	      SetConsoleMode (get_handle (), mode);
 	      if (get_ttyp ()->pcon_pid == 0 ||
-		  kill (get_ttyp ()->pcon_pid, 0) != 0)
+		  !pinfo (get_ttyp ()->pcon_pid))
 		get_ttyp ()->pcon_pid = myself->pid;
 	      get_ttyp ()->switch_to_pcon_in = true;
 	    }
@@ -2739,7 +2739,7 @@ fhandler_pty_slave::fixup_after_attach (bool native_maybe, int fd_set)
 	      if (!get_ttyp ()->switch_to_pcon_out)
 		wait_pcon_fwd ();
 	      if (get_ttyp ()->pcon_pid == 0 ||
-		  kill (get_ttyp ()->pcon_pid, 0) != 0)
+		  !pinfo (get_ttyp ()->pcon_pid))
 		get_ttyp ()->pcon_pid = myself->pid;
 	      get_ttyp ()->switch_to_pcon_out = true;
 
-- 
2.21.0