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authorKees Cook <keescook@chromium.org>2021-10-05 08:26:11 -0700
committerJonathan Corbet <corbet@lwn.net>2021-10-12 13:35:02 -0600
commitd5b421fe0282784a4a8235d549d6ac5d9efff967 (patch)
treefc9412485891b4ccd938f4763793cb345d2c6d26 /Documentation/process
parent7275423c177e5dcf53e350ab9db38f99946b8ec5 (diff)
downloadlinux-d5b421fe0282784a4a8235d549d6ac5d9efff967.tar.gz
docs: Explain the desired position of function attributes
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@chromium.org>
Link: https://lore.kernel.org/r/20211005152611.4120605-1-keescook@chromium.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/process')
-rw-r--r--Documentation/process/coding-style.rst37
1 files changed, 36 insertions, 1 deletions
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@mail.gmail.com/>`_.
+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
 -----------------------------------