[PATCH] bitfield: fix *_encode_bits()

From: Johannes Berg
Date: Thu Jun 14 2018 - 17:25:21 EST

There's a bug in *_encode_bits() in using ~field_multiplier() for
the check whether or not the constant value fits into the field,
this is wrong and clearly ~field_mask() was intended. This was
triggering for me for both constant and non-constant values.

Additionally, make this case actually into an compile error.
Declaring the extern function that will never exist with just a
warning is pointless as then later we'll just get a link error.

While at it, also fix the indentation in those lines I'm touching.

Fixes: 00b0c9b82663 ("Add primitives for manipulating bitfields both in host- and fixed-endian.")
Signed-off-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
If you don't mind, I'd like to take this through the networking
tree(s) as a fix since I have some pending code that depends on
include/linux/bitfield.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index cf2588d81148..4a691a09eb40 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -104,7 +104,7 @@
(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask)); \

-extern void __compiletime_warning("value doesn't fit into mask")
+extern void __compiletime_error("value doesn't fit into mask")
extern void __compiletime_error("bad bitfield mask")
@@ -121,8 +121,8 @@ static __always_inline u64 field_mask(u64 field)
#define ____MAKE_OP(type,base,to,from) \
static __always_inline __##type type##_encode_bits(base v, base field) \
{ \
- if (__builtin_constant_p(v) && (v & ~field_multiplier(field))) \
- __field_overflow(); \
+ if (__builtin_constant_p(v) && (v & ~field_mask(field))) \
+ __field_overflow(); \
return to((v & field_mask(field)) * field_multiplier(field)); \
} \
static __always_inline __##type type##_replace_bits(__##type old, \