bitfield.h uses the left shift operator with a left operand which
may be negative. The C99 standard states that shifting a negative
value is undefined.
We also need to cast the result explicitly into the left hand
side type to deal with:
warning: large integer implicitly truncated to unsigned type [-Woverflow]
Signed-off-by: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
---
lib/bitfield.h | 58 +++++++++++++++++++++++++++++++++++-----------------------
1 file changed, 35 insertions(+), 23 deletions(-)
diff --git a/lib/bitfield.h b/lib/bitfield.h
index a729db99..164e2aaf 100644
--- a/lib/bitfield.h
+++ b/lib/bitfield.h
@@ -43,13 +43,25 @@
#define _bt_is_signed_type(type) (((type)(-1)) < 0)
+/*
+ * NOTE: The unsigned cast ensures that we're not shifting a negative
+ * value, which is undefined in C. However, this limits the maximum
+ * type size of `type` and `v` to 64-bit. The _bt_check_max_64bit() is
+ * used to check that the users of this header do not use types with a
+ * size greater than 64-bit.
+ */
#define _bt_unsigned_cast(type, v) \
({ \
- (sizeof(v) < sizeof(type)) ? \
- ((type) (v)) & (~(~(type) 0 << (sizeof(v) * CHAR_BIT))) : \
- (type) (v); \
+ __builtin_types_compatible_p(type, int8_t) ? (uint8_t) (v) : \
+ __builtin_types_compatible_p(type, int16_t) ? (uint16_t) (v) : \
+ __builtin_types_compatible_p(type, int32_t) ? (uint32_t) (v) : \
+ __builtin_types_compatible_p(type, int64_t) ? (uint64_t) (v) : \
+ (type) (v); \
})
+/* Unsigned bitwise complement. */
+#define _bt_bitwise_not(type, v) _bt_unsigned_cast(type, ~(type) v)
+
/*
* bt_bitfield_write - write integer to a bitfield in native endianness
*
@@ -87,15 +99,15 @@ do {
\
\
/* Trim v high bits */ \
if (__length < sizeof(__v) * CHAR_BIT) \
- __v &= ~((~(typeof(__v)) 0) << __length); \
+ __v &= (__typeof__(__v)) ~(_bt_bitwise_not(typeof(__v), 0) <<
__length); \
\
/* We can now append v with a simple "or", shift it piece-wise */ \
this_unit = start_unit; \
if (start_unit == end_unit - 1) { \
- mask = ~((~(type) 0) << (__start % ts)); \
+ mask = (__typeof__(mask)) ~(_bt_bitwise_not(type, 0) <<
(__start % ts)); \
if (end % ts) \
- mask |= (~(type) 0) << (end % ts); \
- cmask = (type) __v << (__start % ts); \
+ mask |= (__typeof__(mask)) (_bt_bitwise_not(type, 0) <<
(end % ts)); \
+ cmask = (__typeof__(cmask)) (_bt_unsigned_cast(type, __v) <<
(__start % ts)); \
cmask &= ~mask; \
__ptr[this_unit] &= mask; \
__ptr[this_unit] |= cmask; \
@@ -103,8 +115,8 @@ do {
\
} \
if (__start % ts) { \
cshift = __start % ts; \
- mask = ~((~(type) 0) << cshift); \
- cmask = (type) __v << cshift; \
+ mask = (__typeof__(mask)) ~(_bt_bitwise_not(type, 0) <<
cshift); \
+ cmask = (__typeof__(cmask)) (_bt_unsigned_cast(type, __v) <<
cshift); \
cmask &= ~mask; \
__ptr[this_unit] &= mask; \
__ptr[this_unit] |= cmask; \
@@ -118,7 +130,7 @@ do {
\
__start += ts; \
} \
if (end % ts) { \
- mask = (~(type) 0) << (end % ts); \
+ mask = (__typeof__(mask)) (_bt_bitwise_not(type, 0) << (end %
ts)); \
cmask = (type) __v; \
cmask &= ~mask; \
__ptr[this_unit] &= mask; \
@@ -146,15 +158,15 @@ do {
\
\
/* Trim v high bits */ \
if (__length < sizeof(__v) * CHAR_BIT) \
- __v &= ~((~(typeof(__v)) 0) << __length); \
+ __v &= (__typeof__(__v)) ~(_bt_bitwise_not(typeof(__v), 0) <<
__length); \
\
/* We can now append v with a simple "or", shift it piece-wise */ \
this_unit = end_unit - 1; \
if (start_unit == end_unit - 1) { \
- mask = ~((~(type) 0) << ((ts - (end % ts)) % ts)); \
+ mask = (__typeof__(mask)) ~(_bt_bitwise_not(type, 0) << ((ts -
(end % ts)) % ts)); \
if (__start % ts) \
- mask |= (~((type) 0)) << (ts - (__start % ts)); \
- cmask = (type) __v << ((ts - (end % ts)) % ts); \
+ mask |= (__typeof__(mask)) (_bt_bitwise_not(type, 0) <<
(ts - (__start % ts))); \
+ cmask = (__typeof__(cmask)) (_bt_unsigned_cast(type, __v) <<
((ts - (end % ts)) % ts)); \
cmask &= ~mask; \
__ptr[this_unit] &= mask; \
__ptr[this_unit] |= cmask; \
@@ -162,8 +174,8 @@ do {
\
} \
if (end % ts) { \
cshift = end % ts; \
- mask = ~((~(type) 0) << (ts - cshift)); \
- cmask = (type) __v << (ts - cshift); \
+ mask = (__typeof__(mask)) ~(_bt_bitwise_not(type, 0) << (ts -
cshift)); \
+ cmask = (__typeof__(cmask)) (_bt_unsigned_cast(type, __v) <<
(ts - cshift)); \
cmask &= ~mask; \
__ptr[this_unit] &= mask; \
__ptr[this_unit] |= cmask; \
@@ -177,7 +189,7 @@ do {
\
end -= ts; \
} \
if (__start % ts) { \
- mask = (~(type) 0) << (ts - (__start % ts)); \
+ mask = (__typeof__(mask)) (_bt_bitwise_not(type, 0) << (ts -
(__start % ts))); \
cmask = (type) __v; \
cmask &= ~mask; \
__ptr[this_unit] &= mask; \
@@ -250,7 +262,7 @@ do {
\
cmask = __ptr[this_unit]; \
cmask >>= (__start % ts); \
if ((end - __start) % ts) { \
- mask = ~((~(type) 0) << (end - __start)); \
+ mask = (__typeof__(mask)) ~(_bt_bitwise_not(type, 0) <<
(end - __start)); \
cmask &= mask; \
} \
__v = _bt_piecewise_lshift(__v, end - __start); \
@@ -260,7 +272,7 @@ do {
\
} \
if (end % ts) { \
cshift = end % ts; \
- mask = ~((~(type) 0) << cshift); \
+ mask = (__typeof__(mask)) ~(_bt_bitwise_not(type, 0) <<
cshift); \
cmask = __ptr[this_unit]; \
cmask &= mask; \
__v = _bt_piecewise_lshift(__v, cshift); \
@@ -274,7 +286,7 @@ do {
\
end -= ts; \
} \
if (__start % ts) { \
- mask = ~((~(type) 0) << (ts - (__start % ts))); \
+ mask = (__typeof__(mask)) ~(_bt_bitwise_not(type, 0) << (ts -
(__start % ts))); \
cmask = __ptr[this_unit]; \
cmask >>= (__start % ts); \
cmask &= mask; \
@@ -317,7 +329,7 @@ do {
\
cmask = __ptr[this_unit]; \
cmask >>= (ts - (end % ts)) % ts; \
if ((end - __start) % ts) { \
- mask = ~((~(type) 0) << (end - __start)); \
+ mask = (__typeof__(mask)) ~(_bt_bitwise_not(type, 0) <<
(end - __start)); \
cmask &= mask; \
} \
__v = _bt_piecewise_lshift(__v, end - __start); \
@@ -327,7 +339,7 @@ do {
\
} \
if (__start % ts) { \
cshift = __start % ts; \
- mask = ~((~(type) 0) << (ts - cshift)); \
+ mask = (__typeof__(mask)) ~(_bt_bitwise_not(type, 0) << (ts -
cshift)); \
cmask = __ptr[this_unit]; \
cmask &= mask; \
__v = _bt_piecewise_lshift(__v, ts - cshift); \
@@ -341,7 +353,7 @@ do {
\
__start += ts; \
} \
if (end % ts) { \
- mask = ~((~(type) 0) << (end % ts)); \
+ mask = (__typeof__(mask)) ~(_bt_bitwise_not(type, 0) << (end %
ts)); \
cmask = __ptr[this_unit]; \
cmask >>= ts - (end % ts); \
cmask &= mask; \
--
2.11.0
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