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authorKees Cook <keescook@chromium.org>2021-10-05 18:26:11 +0300
committerJonathan Corbet <corbet@lwn.net>2021-10-12 22:35:02 +0300
commitd5b421fe0282784a4a8235d549d6ac5d9efff967 (patch)
treefc9412485891b4ccd938f4763793cb345d2c6d26 /Documentation/process
parent7275423c177e5dcf53e350ab9db38f99946b8ec5 (diff)
downloadlinux-d5b421fe0282784a4a8235d549d6ac5d9efff967.tar.xz
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
-----------------------------------