Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org> Reviewed-by: Richard Henderson <richard.hender...@linaro.org> Signed-off-by: Pierrick Bouvier <pierrick.bouv...@linaro.org> --- docs/devel/style.rst | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)
diff --git a/docs/devel/style.rst b/docs/devel/style.rst index 2f68b500798..d025933808e 100644 --- a/docs/devel/style.rst +++ b/docs/devel/style.rst @@ -416,6 +416,26 @@ 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 lay them out than GCC +<https://gcc.gnu.org/onlinedocs/gcc/x86-Type-Attributes.html>`_, or where +endianness matters. + +For this reason, we disallow usage of bitfields in packed structures and in any +structures which are supposed to exactly match a specific layout in guest +memory. Some existing code may use it, and we carefully ensured the layout was +the one expected. + +We also suggest avoiding bitfields even in structures where the exact +layout does not matter, unless you can show that they provide a significant +usability benefit. + +We encourage the usage of ``include/hw/registerfields.h`` as a safe replacement +for bitfields. + Reserved namespaces in C and POSIX ---------------------------------- -- 2.39.5
