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> --- v5: - drop extern (joe) - fix __malloc position (miguel) v4: https://lore.kernel.org/lkml/20210930235754.2635912-1-keescook@xxxxxxxxxxxx --- Documentation/process/coding-style.rst | 37 +++++++++++++++++++++++++- 1 file changed, 36 insertions(+), 1 deletion(-) diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst index 42969ab37b34..5756ff775233 100644 --- a/Documentation/process/coding-style.rst +++ b/Documentation/process/coding-style.rst @@ -480,13 +480,48 @@ closing function brace line. E.g.: } EXPORT_SYMBOL(system_is_up); +6.1) Function prototypes +************************ + In function prototypes, include parameter names with their data types. Although this is not required by the C language, it is preferred in Linux 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 +Do not use the ``extern`` keyword with function declarations as this makes lines longer and isn't strictly necessary. +When writing function prototypes, please keep the `order of elements regular +<https://lore.kernel.org/mm-commits/CAHk-=wiOCLRny5aifWNhr621kYrJwhfURsa0vFPeUEm8mF0ufg@xxxxxxxxxxxxxx/>`_. +For example, using this function declaration example:: + + __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 (below, ``static __always_inline``, noting that ``__always_inline`` + is technically an attribute but 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** (i.e. the actual function body), +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)`` +below, compared to the **declaration** example above):: + + 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
