linux-kernel - [PATCH v2] bitfield: fix *_encode

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Date:   Thu, 14 Jun 2018 23:26:43 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     linux-kernel@...r.kernel.org
Cc:     Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH v2] bitfield: fix *_encode_bits()

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@...solutions.net>
---
v2: replace stray tab by space

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
it.
---
 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..147a7bb341dd 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")
 __field_overflow(void);
 extern void __compiletime_error("bad bitfield mask")
 __bad_mask(void);
@@ -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,	\
-- 
2.14.4