Re: [patch] Crashed cross gdb/MinGW host

[Daniel Jacobowitz <drow@false.org>]

On Fri, May 19, 2006 at 02:52:57PM -0400, Christopher Faylor wrote:
> On Fri, May 19, 2006 at 06:47:04PM +0900, Masaki Muranaka wrote:
> >My sh-elf-gdb on MinGW host was crashed when I tried to debug using the
> >serial connection.  Here is a patch.
> >
> >It's possible the another plan to remove writefds check.  There is no
> >support yet for writefds.
> 
> If this is truly supposed to be an emulation of the system select(), I
> think it would make sense to check both !readfds and !writefds.

Sorry for letting this sit so long.  I just encountered this bug today. 
I think I tested console and pipe when I last touched this code
but failed to test ser-base.

The underlying problem is actually different.  The code looks like
this:
      if (!FD_ISSET (fd, readfds) && !FD_ISSET (fd, writefds))
        continue;

      if (FD_ISSET (fd, readfds))
	...

      if (FD_ISSET (fd, exceptfds))
	...

See the mismatch? :-(

I have committed the attached patch as obvious.  It adds the missing
NULL checks, and also corrects the loop check for exceptfds.

-- 
Daniel Jacobowitz
CodeSourcery

2006-06-10  Daniel Jacobowitz  <dan@codesourcery.com>

	* mingw-hdep.c (gdb_select): Always check for NULL fd sets
	before calling FD_ISSET.  Correct check for exceptfds which
	previously tested writefds.

Index: mingw-hdep.c
===================================================================
RCS file: /cvs/src/src/gdb/mingw-hdep.c,v
retrieving revision 1.3
diff -u -p -r1.3 mingw-hdep.c
--- mingw-hdep.c	24 Apr 2006 21:00:13 -0000	1.3
+++ mingw-hdep.c	10 Jun 2006 16:37:55 -0000
@@ -105,8 +105,8 @@ gdb_select (int n, fd_set *readfds, fd_s
 	 if something starts using it.  */
       gdb_assert (!writefds || !FD_ISSET (fd, writefds));
 
-      if (!FD_ISSET (fd, readfds)
-	  && !FD_ISSET (fd, exceptfds))
+      if ((!readfds || !FD_ISSET (fd, readfds))
+	  && (!exceptfds || !FD_ISSET (fd, exceptfds)))
 	continue;
       h = (HANDLE) _get_osfhandle (fd);
 
@@ -124,13 +124,13 @@ gdb_select (int n, fd_set *readfds, fd_s
 	  except = never_handle;
 	}
 
-      if (FD_ISSET (fd, readfds))
+      if (readfds && FD_ISSET (fd, readfds))
 	{
 	  gdb_assert (num_handles < MAXIMUM_WAIT_OBJECTS);
 	  handles[num_handles++] = read;
 	}
 
-      if (FD_ISSET (fd, exceptfds))
+      if (exceptfds && FD_ISSET (fd, exceptfds))
 	{
 	  gdb_assert (num_handles < MAXIMUM_WAIT_OBJECTS);
 	  handles[num_handles++] = except;
@@ -169,10 +169,11 @@ gdb_select (int n, fd_set *readfds, fd_s
       HANDLE fd_h;
       struct serial *scb;
 
-      if (!FD_ISSET (fd, readfds) && !FD_ISSET (fd, writefds))
+      if ((!readfds || !FD_ISSET (fd, readfds))
+	  && (!exceptfds || !FD_ISSET (fd, exceptfds)))
 	continue;
 
-      if (FD_ISSET (fd, readfds))
+      if (readfds && FD_ISSET (fd, readfds))
 	{
 	  fd_h = handles[indx++];
 	  /* This handle might be ready, even though it wasn't the handle
@@ -183,7 +184,7 @@ gdb_select (int n, fd_set *readfds, fd_s
 	    num_ready++;
 	}
 
-      if (FD_ISSET (fd, exceptfds))
+      if (exceptfds && FD_ISSET (fd, exceptfds))
 	{
 	  fd_h = handles[indx++];
 	  /* This handle might be ready, even though it wasn't the handle