Re: [PATCH v2] docs: Explain the desired position of function attributes
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From: Joe Perches <joe@perches.com>
Date: 2021-10-01 01:16:59
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linux-hardening, lkml
On Thu, 2021-09-30 at 12:24 -0700, Kees Cook wrote:
quoted hunk ↗ jump to hunk
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/ (local) Signed-off-by: Kees Cook <redacted> --- 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/ (local)>`_. +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
-----------------------------------