[binutils-gdb] gdb/Cygwin: Fix attach pid error message

[Pedro Alves <palves@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=43ca4ec2996a6bfbb8726f1c753aeb85fe0f92a4

commit 43ca4ec2996a6bfbb8726f1c753aeb85fe0f92a4
Author: Pedro Alves <pedro@palves.net>
Date:   Fri Jun 2 23:40:23 2023 +0100

    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:
---
 gdb/windows-nat.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 3b3239ab938..70f955d9797 100644
--- 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