Re: [PATCH] Reserve a slot for argv[0] in default_arg.

From: Jeff King <peff@peff.net>
Date: Oct 4, 2009, 13:33 UTC
Message-ID: <20091004133333.GA13894@sigill.intra.peff.net>
In-Reply-To: <1254576571-29274-1-git-send-email-urkedal@nbi.dk>

On Sat, Oct 03, 2009 at 03:29:31PM +0200, Petter Urkedal wrote:

> Setting "av" to one slot before the allocated "default_arg" array causes
> glibc abort with "free(): invalid next size (normal)" in some
> configurations (Gentoo, glibc-2.9_p20081201-r2, gcc-5.3.2 with PIE).

Thanks, your fix looks sane. But I am curious about whether we are triggering some glibc pickiness that is in your setup, or if we are somehow violating the assumption that we only ever look at default_arg[1] and beyond.

What show-branch command did you issue to hit this? I was hoping to run it under valgrind.

Also:

> +			if (!default_num)
> +			    /* One unused position for argv[0]. */
> +			    default_arg[default_num++] = NULL;

I don't know if we have a style rule for comments on single line conditionals, but I had to read this a few times to make sure it wasn't missing braces.

> -		ac = default_num + 1;
> -		av = default_arg - 1; /* ick; we would not address av[0] */
> +		ac = default_num;
> +		av = default_arg;

Any time you can remove a comment with "ick" in it is probably a good thing. ;)

-Peff