Re: [PATCH v4 2/8] overflow: Add struct_size_with_data() and struct_data_pointer() helpers

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Wed, Feb 28, 2024 at 01:37:36PM -0800, Kees Cook wrote:
> On Wed, Feb 28, 2024 at 10:41:32PM +0200, Andy Shevchenko wrote:

...

> > +#define struct_data_pointer(p, a)	PTR_ALIGN((void *)((p) + 1), (a))
> 
> I'm not super excited about propagating the "p + 1" code pattern to find
> things after an allocation. This leads to the compiler either being
> blind to accesses beyond an allocation, or being too conservative about
> accesses beyond an object. Instead of these helpers I would much prefer
> that data structures that use this code pattern be converted to using
> trailing flexible arrays, at which point the compiler is in a much
> better position to reason about sizes.

There is nothing about flexible arrays in this.
Maybe you have been confused by my choice for name of the macros.
In that case I also can argue that current struct_size() is a good one.
(something like struct_size_with_flex_array() can be more specific)

-- 
With Best Regards,
Andy Shevchenko