Re: [PATCH v1 1/2] overflow: Allow to sum a few arguments at once

[David Laight]

On Tue, 23 Jun 2026 17:09:40 +0300
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:

> On Mon, Jun 22, 2026 at 01:16:29PM +0200, Johannes Berg wrote:
> > On Sat, 2026-06-20 at 09:56 +0300, Andy Shevchenko wrote:  
> > > Johannes, are you okay to take a new version (I assume the wish is to have
> > > the balanced additions)? If so, I will prepare one.  
> > 
> > Sure, I can take the patches, sounds good to me.  
> 
> Will send soon, for the record the *.i file is 61 character less with the patch.
> 
> Was
> 
> size = __builtin_choose_expr((sizeof(int) == sizeof(*(8 ? ((void *)((long)(n_channels) * 0l)) : (int *)8))), sizeof(*(request)) + __builtin_choose_expr((sizeof(int) == sizeof(*(8 ? ((void *)((long)(n_channels) * 0l)) : (int *)8))), (n_channels) * sizeof(*(request)->channels) + ((int)sizeof(struct {_Static_assert(!(!(!__builtin_types_compatible_p(typeof(((request)->channels)), typeof(&((request)->channels)[0])))), "must be array");})), size_mul(n_channels, sizeof(*(request)->channels) + ((int)sizeof(struct {_Static_assert(!(!(!__builtin_types_compatible_p(typeof(((request)->channels)), typeof(&((request)->channels)[0])))), "must be array");})))), __size_add(sizeof(*(request)), __builtin_choose_expr((sizeof(int) == sizeof(*(8 ? ((void *)((long)(n_channels) * 0l)) : (int *)8))), (n_channels) * sizeof(*(request)->channels) + ((int)sizeof(struct {_Static_assert(!(!(!__builtin_types_compatible_p(typeof(((request)->channels)), typeof(&((request)->channels)[0])))), "must be array");})), si
 ze_mul(n_channels, sizeof(*(request)->channels) + ((int)sizeof(struct {_Static_assert(!(!(!__builtin_types_compatible_p(typeof(((request)->channels)), typeof(&((request)->channels)[0])))), "must be array");}))))));
> - size = __size_add(size, size_mul(sizeof(*request->ssids), n_ssids));
> - size = __size_add(size, size_mul(sizeof(*request->match_sets), n_match_sets));
> - size = __size_add(size, size_mul(sizeof(*request->scan_plans), n_plans));
> - size = __size_add(size, ie_len);
> 
> Now
> 
> size = __size_add(__size_add(__size_add(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ? ((void *)((long)(n_channels) * 0l)) : (int *)8))), sizeof(*(request)) + __builtin_choose_expr((sizeof(int) == sizeof(*(8 ? ((void *)((long)(n_channels) * 0l)) : (int *)8))), (n_channels) * sizeof(*(request)->channels) + ((int)sizeof(struct {_Static_assert(!(!(!__builtin_types_compatible_p(typeof(((request)->channels)), typeof(&((request)->channels)[0])))), "must be array");})), size_mul(n_channels, sizeof(*(request)->channels) + ((int)sizeof(struct {_Static_assert(!(!(!__builtin_types_compatible_p(typeof(((request)->channels)), typeof(&((request)->channels)[0])))), "must be array");})))), __size_add(sizeof(*(request)), __builtin_choose_expr((sizeof(int) == sizeof(*(8 ? ((void *)((long)(n_channels) * 0l)) : (int *)8))), (n_channels) * sizeof(*(request)->channels) + ((int)sizeof(struct {_Static_assert(!(!(!__builtin_types_compatible_p(typeof(((request)->channels)), typeof(&((request)->channels)
 [0])))), "must be array");})), size_mul(n_channels, sizeof(*(request)->channels) + ((int)sizeof(struct {_Static_assert(!(!(!__builtin_types_compatible_p(typeof(((request)->channels)), typeof(&((request)->channels)[0])))), "must be array");})))))), ie_len), size_mul(sizeof(*request->ssids), n_ssids)), __size_add(size_mul(sizeof(*request->match_sets), n_match_sets), size_mul(sizeof(*request->scan_plans), n_plans)));
> 

Both those seem to contain multiple expansions of is_constexpr().
I'd be surprised if __builtin_constant_p() wasn't good enough.

I also wonder what kind of mess the object code looks like.

I'd also worry whether the saturating maths in any way performs the correct check.
I suspect the (non-saturated) value gets used for a kmalloc(),
but that has much smaller valid (and sane) limits than can come out of the above.

	David