[RFC] remote-mips.c: Don't error out when a memory read fails

[Kevin Buettner <kevinb@redhat.com>]

The remote-mips.c targets, apparently by design, disconnect from
the board when an error occurs.  This is totally unnecessary in some
cases, such as when reading from an unreadable address.  It is
especially annoying to have GDB disconnect from the board immediately
after connecting due to being unable to figure out the stack frame.
(The program, if any, loaded on the board may not match the symbols
currently loaded into GDB.)

This patch tweaks mips_fetch_word() so that it no longer throws an
error.  Instead, it now returns a status code which the caller must
check.

The caller, mips_xfer_memory(), has been adjusted accordingly.

Comments?

	* remote-mips.c (mips_fetch_word): Add new parameter, `valp'.
	Change return value to int.  Store value fetched in location
	addressed by `val'.  Use function's return value as success
	or failure indicator.  Adjust all callers.

Index: remote-mips.c
===================================================================
RCS file: /cvs/src/src/gdb/remote-mips.c,v
retrieving revision 1.109
diff -u -p -r1.109 remote-mips.c
--- remote-mips.c	5 Mar 2010 16:18:54 -0000	1.109
+++ remote-mips.c	5 Mar 2010 21:57:43 -0000
@@ -91,7 +91,7 @@ static int mips_map_regno (struct gdbarc
 
 static void mips_prepare_to_store (struct regcache *regcache);
 
-static unsigned int mips_fetch_word (CORE_ADDR addr);
+static int mips_fetch_word (CORE_ADDR addr, unsigned int *valp);
 
 static int mips_store_word (CORE_ADDR addr, unsigned int value,
 			    int *old_contents);
@@ -1994,25 +1994,24 @@ mips_store_registers (struct target_ops 
     mips_error ("Can't write register %d: %s", regno, safe_strerror (errno));
 }
 
-/* Fetch a word from the target board.  */
+/* Fetch a word from the target board.  Return word fetched in location
+   addressed by VALP.  Return 0 when successful; return positive error
+   code when not.  */
 
-static unsigned int
-mips_fetch_word (CORE_ADDR addr)
+static int
+mips_fetch_word (CORE_ADDR addr, unsigned int *valp)
 {
   unsigned int val;
   int err;
 
-  val = mips_request ('d', addr, 0, &err, mips_receive_wait, NULL);
+  *valp = mips_request ('d', addr, 0, &err, mips_receive_wait, NULL);
   if (err)
     {
       /* Data space failed; try instruction space.  */
-      val = mips_request ('i', addr, 0, &err,
-			  mips_receive_wait, NULL);
-      if (err)
-	mips_error ("Can't read address %s: %s",
-		    paddress (target_gdbarch, addr), safe_strerror (errno));
+      *valp = mips_request ('i', addr, 0, &err,
+			    mips_receive_wait, NULL);
     }
-  return val;
+  return err;
 }
 
 /* Store a word to the target board.  Returns errno code or zero for
@@ -2078,17 +2077,25 @@ mips_xfer_memory (CORE_ADDR memaddr, gdb
       /* Fill start and end extra bytes of buffer with existing data.  */
       if (addr != memaddr || len < 4)
 	{
+	  unsigned int val;
+
+	  if (mips_fetch_word (addr, &val))
+	    return 0;
+
 	  /* Need part of initial word -- fetch it.  */
-	  store_unsigned_integer (&buffer[0], 4, byte_order,
-				  mips_fetch_word (addr));
+	  store_unsigned_integer (&buffer[0], 4, byte_order, val);
 	}
 
       if (count > 1)
 	{
+	  unsigned int val;
+
 	  /* Need part of last word -- fetch it.  FIXME: we do this even
 	     if we don't need it.  */
-	  store_unsigned_integer (&buffer[(count - 1) * 4], 4, byte_order,
-				  mips_fetch_word (addr + (count - 1) * 4));
+	  if (mips_fetch_word (addr + (count - 1) * 4, &val))
+	    return 0;
+
+	  store_unsigned_integer (&buffer[(count - 1) * 4], 4, byte_order, val);
 	}
 
       /* Copy data to be written over corresponding part of buffer */
@@ -2123,8 +2130,12 @@ mips_xfer_memory (CORE_ADDR memaddr, gdb
       /* Read all the longwords */
       for (i = 0; i < count; i++, addr += 4)
 	{
-	  store_unsigned_integer (&buffer[i * 4], 4, byte_order,
-				  mips_fetch_word (addr));
+	  unsigned int val;
+
+	  if (mips_fetch_word (addr, &val))
+	    return 0;
+
+	  store_unsigned_integer (&buffer[i * 4], 4, byte_order, val);
 	  QUIT;
 	}