Re: [PATCH 3/5] compiler_attributes: Add overflow_behavior macros __ob_trap and __ob_wrap

[Miguel Ojeda]

On Tue, Mar 31, 2026 at 6:37 PM Kees Cook <k...@kernel.org> wrote:
>
> +/*
> + * Optional: only supported by Clang with -Xclang 
> -experimental-foverflow-behavior-types
> + * passed via CONFIG_OVERFLOW_BEHAVIOR_TYPES. When not available, define 
> empty macros for
> + * the trap/wrap annotations.
> + *
> + * clang: https://clang.llvm.org/docs/OverflowBehaviorTypes.html
> + */
> +#if !__has_attribute(overflow_behavior) || !defined(OVERFLOW_BEHAVIOR_TYPES)
> +# define __ob_trap
> +# define __ob_wrap
> +#endif

Should that have `CONFIG_*`? i.e.

     !defined(CONFIG_OVERFLOW_BEHAVIOR_TYPES)

In addition, since this depends on a `CONFIG_`, with the current setup
we would put them elsewhere instead of `compiler_attributes.h` until
they are promoted to be "unconditional" (i.e. without the compiler
flag):

     * Any other "attributes" (i.e. those that depend on a configuration option,
     * on a compiler, on an architecture, on plugins, on other attributes...)
     * should be defined elsewhere (e.g. compiler_types.h or compiler-*.h).
     * The intention is to keep this file as simple as possible, as well as
     * compiler- and version-agnostic (e.g. avoiding GCC_VERSION checks).

However, thinking about it, why is the config needed?

i.e. if the compiler is not passed that flag, shouldn't the
`__has_attribute` simply return false?

Also, I am a bit confused -- does the compiler flag automatically
recognize the names like `__ob_trap`? i.e. I see the docs mention
using the attribute,

    typedef unsigned int __attribute__((overflow_behavior(trap))) safe_uint;
    typedef unsigned int __attribute__((overflow_behavior(wrap))) wrapping_uint;

But then we don't actually use it?

Or should this just be like the rest of the attributes, i.e. we
actually define them here?

Thanks!

Cheers,
Miguel