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

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Date:   Fri, 24 Sep 2021 13:23:02 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jonathan Corbet <corbet@....net>
Cc:     Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Joe Perches <joe@...ches.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] 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 a
synthesized version of Linus's, Joe's, and Rasmus's recommendations on
this subject for future reference.

[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 | 27 ++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst
index 42969ab37b34..3559c34a9281 100644
--- a/Documentation/process/coding-style.rst
+++ b/Documentation/process/coding-style.rst
@@ -487,6 +487,33 @@ 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 prototype, please keep the `order of elements regular
+<https://lore.kernel.org/mm-commits/CAHk-=wiOCLRny5aifWNhr621kYrJwhfURsa0vFPeUEm8mF0ufg@mail.gmail.com>`_. For example::
+
+	__must_check __printf(4, 5) __malloc __init
+	static __always_inline void *action(enum magic value, size_t size,
+					    u8 count, char *fmt, ...)
+	{
+		...
+	}
+
+The preferred order of elements for a function prototype is:
+
+- attributes on the preceding lines
+
+  - return type attributes (here, ``__must_check``)
+  - function parameter attributes (here, ``__printf(4,5)``)
+  - function behavior attributes (here, ``__malloc``)
+  - storage class attributes (here, ``__init``)
+
+- main function prototype on the next lines
+
+  - storage class (here, ``static __always_inline`` -- even though
+    ``__always_inline`` is technically an attribute, it is treated like
+    ``inline``)
+  - return type (here, ``void *``)
+  - function name (here, ``action``)
+  - function parameters (as described earlier: each with type and name)
 
 7) Centralized exiting of functions
 -----------------------------------
-- 
2.30.2