Re: GLib version requirement

[sfeam <sf...@us...>]

On Thursday, 10 May 2018 09:31:32 Allin Cottrell wrote:
> I see that since 2017-02-09 gnuplot requires version 2.28 or higher of 
> GLib, on account of use of the macro g_clear_object.
> 
> Unfortunately it can be difficult to build GLib on (or for) some older 
> systems, such as OS X <= 10.4, but older GLib versions are easier 
> (e.g. 2.18). I'd like to suggest pushing the GLib dependency back to 
> 2.18 and adding a simple compatibility macro in gp_cairo.c. Here's an
> illustrative diff relative to 5.2.3:
> 
> --- gp_cairo.c.orig 2018-05-09 16:46:59.510301745 -0400
> +++ gp_cairo.c 2018-05-10 08:32:07.378541918 -0400
> @@ -77,6 +77,13 @@
>   #define rint(x) floor((x)+0.5L)
>   #endif
> 
> +#if GLIB_MAJOR_VERSION == 2 && GLIB_MINOR_VERSION < 28
> +#define g_clear_object(op) \
> +    { gpointer *_p = (gpointer) (op); \
> +    if (_p && *_p) { g_object_unref(*_p); *_p = NULL; } \
> +    }
> +#endif
> +
>   /* undef this to see what happens without the Symbol-to-unicode processing */
>   #define MAP_SYMBOL
> 
> Any thoughts?

The change to use g_clear_object fixed detectable use-after-free errors.
Your proposed macro goes back to calling g_object_unref without any
separate reference counting, so I imagine it would reintroduce the
use-after-free errors.  Have you checked?  Or maybe the need for
reference counting was introduced in some later version of glib?

	Ethan