[PATCH 01/22] bitfield.h: Fix "type of reg too small for mask" test

Peter Zijlstra
2021-11-05T17:24:42Z

The test: 'mask > (typeof(_reg))~0ull' only works correctly when both
sides are unsigned, consider:

- 0xff000000 vs (int)~0ull
- 0x000000ff vs (int)~0ull

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/bitfield.h | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)

--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -41,6 +41,22 @@

#define __bf_shf(x) (__builtin_ffsll(x) - 1)

+#define __scalar_type_to_unsigned_cases(type) \
+ unsigned type: (unsigned type)0, \
+ signed type: (unsigned type)0
+
+#define __unsigned_scalar_typeof(x) typeof( \
+ _Generic((x), \
+ char: (unsigned char)0, \
+ __scalar_type_to_unsigned_cases(char), \
+ __scalar_type_to_unsigned_cases(short), \
+ __scalar_type_to_unsigned_cases(int), \
+ __scalar_type_to_unsigned_cases(long), \
+ __scalar_type_to_unsigned_cases(long long), \
+ default: (x)))
+
+#define __bf_cast_unsigned(type, x) ((__unsigned_scalar_typeof(type))(x))
+
#define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx) \
({ \
BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), \
@@ -49,7 +65,8 @@
BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ? \
~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
_pfx "value too large for the field"); \
- BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull, \
+ BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) > \
+ __bf_cast_unsigned(_reg, ~0ull), \
_pfx "type of reg too small for mask"); \
__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) + \
(1ULL << __bf_shf(_mask))); \