Support SIGTRAP in kill emulation on Windows

* src/w32proc.c (sys_kill): Translate SIGTRAP signal into a call to
'DebugBreakProcess' to cause a breakpoint exception to occur in the
specified process.  On Windows versions prior to Windows XP that do
not support 'DebugBreakProcess' return -1 and set errno to ENOTSUP
(as opposed to EINVAL before this change).
* src/w32proc.c: Add typedef for 'DebugBreakProcess' function pointer
and global variable to track state of run-time dynamic linking of this
function.

* etc/NEWS: Add entry to document that 'signal-process' now supports
SIGTRAP.

2 files changed, 51 insertions, 3 deletions

diff --git a/src/w32.c b/src/w32.c
index f9110853799..517e286eaa9 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -334,6 +334,7 @@ static BOOL g_b_init_set_named_security_info_a;
 static BOOL g_b_init_get_adapters_info;
 
 BOOL g_b_init_compare_string_w;
+BOOL g_b_init_debug_break_process;
 
 /*
   BEGIN: Wrapper functions around OpenProcessToken
@@ -9657,6 +9658,7 @@ globals_of_w32 (void)
   g_b_init_set_named_security_info_a = 0;
   g_b_init_get_adapters_info = 0;
   g_b_init_compare_string_w = 0;
+  g_b_init_debug_break_process = 0;
   num_of_processors = 0;
   /* The following sets a handler for shutdown notifications for
      console apps. This actually applies to Emacs in both console and
diff --git a/src/w32proc.c b/src/w32proc.c
index aef4e44d73a..189034c4e2d 100644
--- a/src/w32proc.c
+++ b/src/w32proc.c
@@ -69,6 +69,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
             + (filedata).file_base))
 
 extern BOOL g_b_init_compare_string_w;
+extern BOOL g_b_init_debug_break_process;
+
 int sys_select (int, SELECT_TYPE *, SELECT_TYPE *, SELECT_TYPE *,
                 struct timespec *, void *);
 
@@ -2497,6 +2499,9 @@ find_child_console (HWND hwnd, LPARAM arg)
   return TRUE;
 }
 
+typedef BOOL (WINAPI * DebugBreakProcess_Proc) (
+    HANDLE hProcess);
+
 /* Emulate 'kill', but only for other processes.  */
 int
 sys_kill (pid_t pid, int sig)
@@ -2510,9 +2515,9 @@ sys_kill (pid_t pid, int sig)
   if (pid < 0)
     pid = -pid;
 
-  /* Only handle signals that will result in the process dying */
+  /* Only handle signals that can be mapped to a similar behavior on Windows */
   if (sig != 0
-      && sig != SIGINT && sig != SIGKILL && sig != SIGQUIT && sig != SIGHUP)
+      && sig != SIGINT && sig != SIGKILL && sig != SIGQUIT && sig != SIGHUP && sig != SIGTRAP)
     {
       errno = EINVAL;
       return -1;
@@ -2555,7 +2560,11 @@ sys_kill (pid_t pid, int sig)
          close the selected frame, which does not necessarily
          terminates Emacs.  But then we are not supposed to call
          sys_kill with our own PID.  */
-      proc_hand = OpenProcess (PROCESS_TERMINATE, 0, pid);
+
+      DWORD desiredAccess =
+        (sig == SIGTRAP) ? PROCESS_ALL_ACCESS : PROCESS_TERMINATE;
+
+      proc_hand = OpenProcess (desiredAccess, 0, pid);
       if (proc_hand == NULL)
         {
           errno = EPERM;
@@ -2651,6 +2660,43 @@ sys_kill (pid_t pid, int sig)
           rc = -1;
         }
     }
+  else if (sig == SIGTRAP)
+    {
+      static DebugBreakProcess_Proc s_pfn_Debug_Break_Process = NULL;
+
+      if (g_b_init_debug_break_process == 0)
+        {
+          g_b_init_debug_break_process = 1;
+          s_pfn_Debug_Break_Process = (DebugBreakProcess_Proc)
+            GetProcAddress (GetModuleHandle ("kernel32.dll"),
+                            "DebugBreakProcess");
+        }
+
+      if (s_pfn_Debug_Break_Process == NULL)
+        {
+          errno = ENOTSUP;
+          rc = -1;
+        }
+      else if (!s_pfn_Debug_Break_Process (proc_hand))
+        {
+          DWORD err = GetLastError ();
+
+          DebPrint (("sys_kill.DebugBreakProcess return %d "
+                     "for pid %lu\n", err, pid));
+
+          switch (err)
+            {
+            case ERROR_ACCESS_DENIED:
+              errno = EPERM;
+              break;
+            default:
+              errno = EINVAL;
+              break;
+            }
+
+          rc = -1;
+        }
+    }
   else
     {
       if (NILP (Vw32_start_process_share_console) && cp && cp->hwnd)