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Re: [OB] cli/cli-script.c, null ptr guard
- From: Daniel Jacobowitz <drow at false dot org>
- To: msnyder at sonic dot net
- Cc: gdb-patches at sourceware dot org
- Date: Sun, 1 Jul 2007 11:55:43 -0400
- Subject: Re: [OB] cli/cli-script.c, null ptr guard
- References: <13902.12.7.175.2.1183067383.squirrel@webmail.sonic.net> <20070628215829.GA10350@caradoc.them.org> <6989.12.7.175.2.1183069038.squirrel@webmail.sonic.net> <20070628224250.GB12578@caradoc.them.org> <10837.12.7.175.2.1183071869.squirrel@webmail.sonic.net>
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;
}