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

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=3a71c46380f2cad6a9cb9d182c117cb624214553

commit 3a71c46380f2cad6a9cb9d182c117cb624214553
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Thu Feb 6 19:48:17 2020 +0900

    Cygwin: pty: Use pinfo() rather than kill() with signal 0.
    
    - 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().

Diff:
---
 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 9270c83..82527ec 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 1dd57b3..181bed5 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;