Re: [PATCH 2/3] compiler.h: Introduce __must_be_char_array()

[Kent Overstreet]

On Thu, Feb 06, 2025 at 10:11:29AM -0800, Kees Cook wrote:
> In preparation for adding stricter type checking to the str/mem*()
> helpers, provide a way to check that a variable is a character array
> via __must_be_char_array().
> 
> Signed-off-by: Kees Cook <kees@xxxxxxxxxx>

Suggested-by? :)

> ---
>  include/linux/compiler.h | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 7af999a131cb..a577fe0b1f8a 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -221,7 +221,13 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
>  #endif /* __CHECKER__ */
>  
>  /* &a[0] degrades to a pointer: a different type from an array */
> -#define __must_be_array(a)	__BUILD_BUG_ON_ZERO_MSG(__same_type((a), &(a)[0]), "must be array")
> +#define __is_array(a)		(!__same_type((a), &(a)[0]))
> +#define __must_be_array(a)	__BUILD_BUG_ON_ZERO_MSG(!__is_array(a), \
> +							"must be array")
> +
> +#define __is_char_array(a)	(__is_array(a) && sizeof((a)[0]) == 1)
> +#define __must_be_char_array(a)	__BUILD_BUG_ON_ZERO_MSG(!__is_char_array(a), \
> +							"must be byte array")
>  
>  /* Require C Strings (i.e. NUL-terminated) lack the "nonstring" attribute. */
>  #define __must_be_cstr(p) \
> -- 
> 2.34.1
>