Re: [PATCH 5/5] types: Add standard __ob_trap and __ob_wrap scalar types

Peter Zijlstra
2026-04-01T08:57:22Z

On Tue, Mar 31, 2026 at 01:31:16PM -0700, Kees Cook wrote:

> int func()
> {
> ...
> u8 __ob_trap product = 5;
> ...
> product = a * b; // if store is truncated, goto __overflow
> ...
> return product;
>
> __overflow:
> pr_info("%u\n", product); // shows "5"

I'm confused by this 'product is still 5' thing. It seems to me that
making this happen will, in general, require more instructions/registers
than allowing the old value to be clobbered and have product be the
truncated result of whatever overflow.

Specifically, what is the value of preserving the old value?

> return -1;
> }