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

[Kees Cook <kees@kernel.org>]

On Wed, Jun 17, 2026 at 01:12:36PM +0200, Andy Shevchenko wrote:
> Convert size_add() to take variadic argument, so we can simplify users
> with using a macro only once.

Oh, this is fun. I like it. :)

> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  include/linux/overflow.h | 37 ++++++++++++++++++++++++++-----------
>  1 file changed, 26 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index a8cb6319b4fb..a8b0325e73f3 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -2,9 +2,10 @@
>  #ifndef __LINUX_OVERFLOW_H
>  #define __LINUX_OVERFLOW_H
>  
> +#include <linux/args.h>
>  #include <linux/compiler.h>
> -#include <linux/limits.h>
>  #include <linux/const.h>
> +#include <linux/limits.h>
>  
>  /*
>   * We need to compute the minimum and maximum values representable in a given
> @@ -337,16 +338,7 @@ static __always_inline size_t __must_check size_mul(size_t factor1, size_t facto
>  	return bytes;
>  }
>  
> -/**
> - * size_add() - Calculate size_t addition with saturation at SIZE_MAX
> - * @addend1: first addend
> - * @addend2: second addend
> - *
> - * Returns: calculate @addend1 + @addend2, both promoted to size_t,
> - * with any overflow causing the return value to be SIZE_MAX. The
> - * lvalue must be size_t to avoid implicit type conversion.
> - */
> -static __always_inline size_t __must_check size_add(size_t addend1, size_t addend2)
> +static __always_inline size_t __must_check __size_add(size_t addend1, size_t addend2)
>  {
>  	size_t bytes;
>  
> @@ -356,6 +348,29 @@ static __always_inline size_t __must_check size_add(size_t addend1, size_t adden
>  	return bytes;
>  }
>  
> +#define __size_add0(addend1, ...)						\
> +	__size_add(addend1, 0)
> +#define __size_add1(addend1, addend2, ...)					\
> +	__size_add(addend1,  addend2)
> +#define __size_add2(addend1, addend2, addend3, ...)				\
> +	__size_add(__size_add(addend1,  addend2), addend3)
> +#define __size_add3(addend1, addend2, addend3, addend4, ...)			\
> +	__size_add(__size_add2(addend1,  addend2, addend3), addend4)
> +#define __size_add4(addend1, addend2, addend3, addend4, addend5, ...)		\
> +	__size_add(__size_add3(addend1,  addend2, addend3, addend4), addend5)

Is 4 the max seen in practice?


-- 
Kees Cook