On Fri, Dec 07, 2018 at 02:52:48PM +0000, Wilco Dijkstra wrote:
> - struct __attribute__((aligned (32))) S { int a[4]; } s;
>
> - bar (&s);
>
Any reason to remove the above?
> p = __builtin_alloca (x);
> + q = __builtin_alloca (x);
> if (!__builtin_setjmp (buf))
> broken_longjmp (buf);
>
> + /* Compute expected next alloca offset - some targets don't align properly
> + and allocate too much. */
> + p = q + (q - p);
This is UB, pointer difference is only defined within the same object.
So, you can only do such subtraction in some integral type rather than as
pointer subtraction.
> +
> /* Fails if stack pointer corrupted. */
> - q = __builtin_alloca (x);
> - if (foo (p) < foo (q))
> - {
> - if (foo (q) - foo (p) >= 1024)
> - abort ();
> - }
> - else if (foo (p) - foo (q) >= 1024)
> + if (p != __builtin_alloca (x))
And I'm not sure you have a guarantee that every zero sized alloca is at the
same offset from the previous one.
Jakub
