Re: glib: alloca brain damages

[Tim Janik <timj gtk org>]

On Mon, 4 Jan 1999, Elliot Lee wrote:

> 1.
> 
> #  define g_new0_a(type, count)	  \
>       ((type *) memset (alloca ((unsigned) sizeof (type) * (count)), 0, \
>       			((unsigned) sizeof (type) * (count))))
> 
> Very bad - this is allocating a place on the stack while the compiler is
> trying to set up the stack for the function call. It should be something
> like
> 
> #  define g_new0_a(type, count)	\
> 	G_STMT_STRT { \
> 		char *newblock;
> 		newblock = alloca(sizeof(type) * count);
> 		memset(newblock, 0, sizeof(type) * count);
> 	} G_STMT_END
> 
> 
> The problem is that G_STMT_STRT casts the block to (void), and ANSI C does
> not permit ({expr;}), so there's really no way to do it portably.
> 
> 2. There's the whole problem of doing all these macros at all. On some
> arches/OS's, alloca() won't work inside conditionals, or inside {} blocks.

hm, sopwith, can you eventually provide concrete reports about such
behaviour? we shouldn't provide alloca using macros at all if that's affecting
any system that glib currently runs on.

> 
> MHO is that the only thing that glib should be doing is ensuring that
> alloca() exists and works, nothing more. The actual usage should be done
> directly by the programmer.
> 
> -- Elliot

---
ciaoTJ