gdb/Cygwin: Fix attach pid error message

On Cygwin, with "attach PID":

 - GDB first tries to interpret PID as a Windows native PID, and tries
   to attach to that.

 - if the attach fails, GDB then tries to interpret the PID as a
   Cygwin PID, and attach to that.

If converting the user-provided PID from a Cygwin PID to a Windows PID
fails, you get this:

 (gdb) attach 12345
 Can't attach to process 0 (error 2: The system cannot find the file specified.)

Note "process 0".

With the fix in this commit, we'll now get:

 (gdb) attach 12345
 Can't attach to process 12345 (error 2: The system cannot find the file specified.)

I noticed this while looking at gdb.log after running
gdb.base/attach.exp on Cygwin.

Change-Id: I05b9dc1f3a634a822ea49bb5c61719f5e62c8514
Approved-By: Luis Machado <luis.machado@arm.com>

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 3b3239ab938cb5cee61e5d97e1178a07b19da1cc..70f955d9797883600376e913e63446fb0d0a3aa7 100644 (file)
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -2048,11 +2048,20 @@ windows_nat_target::attach (const char *args, int from_tty)
 #ifdef __CYGWIN__
       if (!ok)
        {
-         /* Try fall back to Cygwin pid.  */
-         pid = cygwin_internal (CW_CYGWIN_PID_TO_WINPID, pid);
+         /* Maybe PID was a Cygwin PID.  Try the corresponding native
+            Windows PID.  */
+         DWORD winpid = cygwin_internal (CW_CYGWIN_PID_TO_WINPID, pid);
 
-         if (pid > 0)
-           ok = DebugActiveProcess (pid);
+         if (winpid != 0)
+           {
+             /* It was indeed a Cygwin PID.  Fully switch to the
+                Windows PID from here on.  We don't do this
+                unconditionally to avoid ending up with PID=0 in the
+                error message below.  */
+             pid = winpid;
+
+             ok = DebugActiveProcess (winpid);
+           }
        }
 #endif