Messages in this thread | | | Date | Mon, 22 Nov 2021 17:17:39 -0800 | From | Jakub Kicinski <> | Subject | Re: [PATCH 01/17] bitfield: Add non-constant field_{prep,get}() helpers |
| |
On Mon, 22 Nov 2021 17:32:43 +0100 Johannes Berg wrote: > On Mon, 2021-11-22 at 16:53 +0100, Geert Uytterhoeven wrote: > > The existing FIELD_{GET,PREP}() macros are limited to compile-time > > constants. However, it is very common to prepare or extract bitfield > > elements where the bitfield mask is not a compile-time constant. > > I'm not sure it's really a good idea to add a third API here?
+1
> We have the upper-case (constant) versions, and already > {u32,...}_get_bits()/etc. > > Also, you're using __ffs(), which doesn't work for 64-bit on 32-bit > architectures (afaict), so that seems a bit awkward. > > Maybe we can make {u32,...}_get_bits() be doing compile-time only checks > if it is indeed a constant? The __field_overflow() usage is already only > done if __builtin_constant_p(v), so I guess we can do the same with > __bad_mask()?
Either that or add decomposition macros. Are compilers still really bad at passing small structs by value?
| |