[lttng-dev] [PATCH babeltrace] Fix: bitfield: left shift undefined behavior
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Tue May 7 16:40:39 EDT 2019
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.desnoyers at efficios.com>
---
include/babeltrace/bitfield-internal.h | 61 ++++++++++++++++++----------------
1 file changed, 33 insertions(+), 28 deletions(-)
diff --git a/include/babeltrace/bitfield-internal.h b/include/babeltrace/bitfield-internal.h
index c5d5eccd..da56f089 100644
--- a/include/babeltrace/bitfield-internal.h
+++ b/include/babeltrace/bitfield-internal.h
@@ -55,19 +55,24 @@
#define _bt_is_signed_type(type) ((type) -1 < (type) 0)
/*
- * NOTE: The cast to (uint64_t) below ensures that we're not casting 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.
+ * 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) (~(~(uint64_t) 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)
+
#define _bt_check_max_64bit(type) \
char _max_64bit_assertion[sizeof(type) <= sizeof(uint64_t) ? 1 : -1] __attribute__((unused))
@@ -108,15 +113,15 @@ 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; \
@@ -124,8 +129,8 @@ 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; \
@@ -139,7 +144,7 @@ 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; \
@@ -167,15 +172,15 @@ 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; \
@@ -183,8 +188,8 @@ 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; \
@@ -198,7 +203,7 @@ 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; \
@@ -275,7 +280,7 @@ 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); \
@@ -285,7 +290,7 @@ 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); \
@@ -299,7 +304,7 @@ 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; \
@@ -346,7 +351,7 @@ 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); \
@@ -356,7 +361,7 @@ 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); \
@@ -370,7 +375,7 @@ 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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