Re: [PATCH v2 2/3] docs/devel/style: add a section about bitfield, and disallow them for packed structures

[Pierrick Bouvier]

On 11/26/24 22:38, Thomas Huth wrote:
> On 26/11/2024 22.17, Pierrick Bouvier wrote:
> > Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> > ---
> >    docs/devel/style.rst | 10 ++++++++++
> >    1 file changed, 10 insertions(+)
> >
> > diff --git a/docs/devel/style.rst b/docs/devel/style.rst
> > index 2f68b500798..13cb1ef626b 100644
> > --- a/docs/devel/style.rst
> > +++ b/docs/devel/style.rst
> > @@ -416,6 +416,16 @@ definitions instead of typedefs in headers and function 
> > prototypes; this
> >    avoids problems with duplicated typedefs and reduces the need to include
> >    headers from other headers.
> >    
> > +Bitfields
> > +---------
> > +
> > +C bitfields can be a cause of non-portability issues, especially under windows
> > +where `MSVC has a different way to layout them than gcc
> > +<https://gcc.gnu.org/onlinedocs/gcc/x86-Type-Attributes.html>`_.
> > +For this reason, we disallow usage of bitfields in packed structures.
>
> I'd maybe add a "in new code" in above sentence - otherwise people will
> complain that there are pre-existing examples with packed structures that
> have bitfields in them.
>
>    Thomas

I'll add this, with other changes Peter suggested.

> > +For general usage, using bitfields should be proven to add significant benefits
> > +regarding memory usage or usability.
> > +
> >    Reserved namespaces in C and POSIX
> >    ----------------------------------
> >