linux-hardening - Re: [PATCH v2] docs: Explain the desired position of function attributes

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Date:   Thu, 30 Sep 2021 18:16:53 -0700
From:   Joe Perches <joe@...ches.com>
To:     Kees Cook <keescook@...omium.org>, Jonathan Corbet <corbet@....net>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] docs: Explain the desired position of function
 attributes

On Thu, 2021-09-30 at 12:24 -0700, Kees Cook 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@mail.gmail.com/
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  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..6b4feb1c71e7 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@mail.gmail.com/>`_.
> +For example::
> +
> + extern __init void * __must_check void action(enum magic value, size_t size,
> + 	u8 count, char *fmt, ...) __printf(4, 5) __malloc;
> +

Read the paragraph above.  extern should not be used in an example.

> +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 void action(
> + 		enum magic value, size_t size, u8 count, char *fmt, ...)
> + 		__malloc
> + {
> + 	...
> + }
>  
> 
>  7) Centralized exiting of functions
>  -----------------------------------