Re: [OB] cli/cli-script.c, null ptr guard

[Daniel Jacobowitz <drow@false.org>]

On Thu, Jun 28, 2007 at 04:04:29PM -0700, Michael Snyder wrote:
> > On Thu, Jun 28, 2007 at 03:17:18PM -0700, msnyder@sonic.net wrote:
> >> > No, I don't think this is obvious.  What does it mean to have a null
> >> > string here and how can it happen?  I'm pretty sure it can't, and the
> >> > if check is just clutter.
> >>
> >> The reasoning is that, since we checked it for NULL in the
> >> first statement of the function, we must believe that the
> >> possibility exists for it to be NULL.
> >
> > Right.  So, is it a sensible check?  Or should it be removed, or
> > should the condition for the error be simplified?
> 
> Well, it either makes sense to check it for null, or it doesn't.
> If the new test is redundant, so is the old one.  Whoever wrote
> it in the first place seemed to think it was worth checking.
> 
> This is called from a number of places, but they are all local to the module.
> 
> Ultimately the argument comes from the command parser.
> It's one of those typical (char *args, int from_tty) things.

There's four calls to build_command_line.  Three are passed a freshly
incremented pointer, so it can never be NULL.  That's
if/while/commands.  The other one came from get_command_line.  Those
can be NULL - well, I'm not sure, but I think they can.  They're
always if/while.

So how about adding gdb_assert (args != NULL) after the error call,
like below?  If you follow where the result of this function goes,
if we actually set cmd->line = NULL we will crash.

-- 
Daniel Jacobowitz
CodeSourcery

2007-07-01  Daniel Jacobowitz  <dan@codesourcery.com>

	* cli/cli-script.c (build_command_line): Update NULL check.

Index: cli/cli-script.c
===================================================================
RCS file: /cvs/src/src/gdb/cli/cli-script.c,v
retrieving revision 1.41
diff -u -p -r1.41 cli-script.c
--- cli/cli-script.c	28 Jun 2007 21:48:54 -0000	1.41
+++ cli/cli-script.c	1 Jul 2007 15:55:26 -0000
@@ -85,6 +85,7 @@ build_command_line (enum command_control
 
   if (args == NULL && (type == if_control || type == while_control))
     error (_("if/while commands require arguments."));
+  gdb_assert (args != NULL);
 
   cmd = (struct command_line *) xmalloc (sizeof (struct command_line));
   cmd->next = NULL;
@@ -95,8 +96,7 @@ build_command_line (enum command_control
     = (struct command_line **) xmalloc (sizeof (struct command_line *)
 					* cmd->body_count);
   memset (cmd->body_list, 0, sizeof (struct command_line *) * cmd->body_count);
-  if (args != NULL)
-    cmd->line = savestring (args, strlen (args));
+  cmd->line = savestring (args, strlen (args));
 
   return cmd;
 }