| Message ID | 20210930192417.1332877-1-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] docs: Explain the desired position of function attributes | expand |
On 9/30/21 12:24 PM, Kees Cook wrote: > 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> > --- > 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/>`_. > +For example:: > + > + extern __init void * __must_check void action(enum magic value, size_t size, Drop that second "void" ? or what does it mean? Can __must_check and void be used together? > + u8 count, char *fmt, ...) __printf(4, 5) __malloc; > + > +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``) I'm not trying to get you to change this, but I would prefer to see extern __init __must_check void *action(...) <attributes>; i.e., with the return type adjacent to the function name. > +- 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 > ----------------------------------- > thanks.
On Thu, Sep 30, 2021 at 01:11:34PM -0700, Randy Dunlap wrote: > On 9/30/21 12:24 PM, Kees Cook wrote: > > 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> > > --- > > 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/>`_. > > +For example:: > > + > > + extern __init void * __must_check void action(enum magic value, size_t size, > > Drop that second "void" ? or what does it mean? > Can __must_check and void be used together? Gah, thanks. Fixed now in v3. > > > + u8 count, char *fmt, ...) __printf(4, 5) __malloc; > > + > > +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``) > > I'm not trying to get you to change this, but I would prefer to see > > extern __init __must_check void *action(...) <attributes>; > > i.e., with the return type adjacent to the function name. I have read and re-read Linus's emails, and did a frequency count in the kernel, and it looks like the preference is [return type] [return type attrs] but I personally agree with you. :) # regex I built from __must_check hits... $ re='((struct .*|void|char) \* ?|((unsigned )?(long|int)|bool|size_t)($| ))' # type before __must_check $ git grep -E "$re"'__must_check' | wc -l 746 # type after __must_check $ git grep -E '\b(static (__always_)?inline )?__must_check($| '"$re"')' | wc -l 297 # type split(!) across __must_check or otherwise weird... $ git grep -E '\b__must_check\b' | grep -Ev '\b(static (__always_)?inline )?__must_check($| '"$re"')' | grep -Ev "$re"'__must_check\b' | wc -l 44
On Thu, 2021-09-30 at 12:24 -0700, Kees Cook wrote: > 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> > --- > 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/>`_. > +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 > -----------------------------------
On Thu, 2021-09-30 at 15:52 -0700, Kees Cook wrote: > I have read and re-read Linus's emails, and did a frequency count in the > kernel, and it looks like the preference is [return type] [return type attrs] Please don't read too much into frequency counts as it really depends on age of code. > but I personally agree with you. :) > > # regex I built from __must_check hits... > $ re='((struct .*|void|char) \* ?|((unsigned )?(long|int)|bool|size_t)($| ))' > > # type before __must_check > $ git grep -E "$re"'__must_check' | wc -l > 746 > > # type after __must_check > $ git grep -E '\b(static (__always_)?inline )?__must_check($| '"$re"')' | wc -l > 297 Hmm. $ git grep -w __must_check -- '*.[ch]' | wc -l 909
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/>`_. +For example:: + + extern __init void * __must_check void 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 (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 -----------------------------------
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> --- Documentation/process/coding-style.rst | 30 ++++++++++++++++++++++++++ 1 file changed, 30 insertions(+)