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?