Re: [PATCH v4] docs: Explain the desired position of function attributes

[Nick Desaulniers]

On Thu, Sep 30, 2021 at 4:58 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> While discussing how to format the addition of various function
> attributes, some "unwritten rules" of ordering surfaced[1]. Capture as
> close as possible to Linus's preferences for future reference.
>
> (Though I note the dissent voiced by Joe Perches, Alexey Dobriyan, and
> others that would prefer all attributes live on a separate leading line.)
>
> [1] https://lore.kernel.org/mm-commits/CAHk-=wiOCLRny5aifWNhr621kYrJwhfURsa0vFPeUEm8mF0ufg@xxxxxxxxxxxxxx/
>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

While I appreciate you getting the ball across the finish line (having
_any_ documentation to point to in future bikesheds), I can't help but
shake the feeling that the chosen policy will harm the ability of
existing automated code formatting tools from being able to automate
code formatting on the kernel.

> ---
> v4:
> - fix another stray "void"! This is why code needs a compiler... (thx randy)
> ---
>  Documentation/process/coding-style.rst | 30 ++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
>
> diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst
> index 42969ab37b34..45b48510f5ec 100644
> --- a/Documentation/process/coding-style.rst
> +++ b/Documentation/process/coding-style.rst
> @@ -487,6 +487,36 @@ because it is a simple way to add valuable information for the reader.
>  Do not use the ``extern`` keyword with function prototypes as this makes
>  lines longer and isn't strictly necessary.
>
> +When writing a function declarations, please keep the `order of elements regular
> +<https://lore.kernel.org/mm-commits/CAHk-=wiOCLRny5aifWNhr621kYrJwhfURsa0vFPeUEm8mF0ufg@xxxxxxxxxxxxxx/>`_.
> +For example::
> +
> + extern __init void * __must_check action(enum magic value, size_t size, u8 count,
> +                                         char *fmt, ...) __printf(4, 5) __malloc;
> +
> +The preferred order of elements for a function prototype is:
> +
> +- storage class (here, ``extern``, and things like ``static __always_inline`` even though
> +  ``__always_inline`` is technically an attribute, it is treated like ``inline``)
> +- storage class attributes (here, ``__init`` -- i.e. section declarations, but also things like ``__cold``)
> +- return type (here, ``void *``)
> +- return type attributes (here, ``__must_check``)
> +- function name (here, ``action``)
> +- function parameters (here, ``(enum magic value, size_t size, u8 count, char *fmt, ...)``, noting that parameter names should always be included)
> +- function parameter attributes (here, ``__printf(4, 5)``)
> +- function behavior attributes (here, ``__malloc``)
> +
> +Note that for a function definition (e.g. ``static inline``), the compiler does
> +not allow function parameter attributes after the function parameters. In these
> +cases, they should go after the storage class attributes (e.g. note the changed
> +position of ``__printf(4, 5)``)::
> +
> + static __always_inline __init __printf(4, 5) void * __must_check action(enum magic value,
> +               size_t size, u8 count, char *fmt, ...)
> +               __malloc
> + {
> +       ...
> + }
>
>  7) Centralized exiting of functions
>  -----------------------------------
> --
> 2.30.2
>


-- 
Thanks,
~Nick Desaulniers