From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Add shift_overflow() helper to help driver authors to ensure that
shift operand doesn't cause to overflow.
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxxxx>
---
include/linux/overflow.h | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 8712ff70995f..21ff032773e0 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -202,6 +202,29 @@
#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
+/*
+ * Compute *d = (a << s)
+ *
+ * Returns true if '*d' cannot hold the result or 'a << s' doesn't make sense.
+ * - 'a << s' causes bits to be lost when stored in d
+ * - 's' is garbage (eg negative) or so large that a << s is guaranteed to be 0
+ * - 'a' is negative
+ * - 'a << s' sets the sign bit, if any, in '*d'
+ * *d is not defined if false is returned.
+ */
+#define check_shift_overflow(a, s, d) ({ \
+ typeof(a) _a = a; \
+ typeof(s) _s = s; \
+ typeof(d) _d = d; \
+ u64 _a_full = _a; \
+ unsigned int _to_shift = \
+ _s >= 0 && _s < 8 * sizeof(*d) ? _s : 0; \
+ *_d = (_a_full << _to_shift); \
+ *d = *_d; \
+ (_to_shift != _s || *_d < 0 || _a < 0 || \
+ (*_d >> _to_shift) != _a); \
+})
+
/**
* array_size() - Calculate size of 2-dimensional array.
*
--
2.14.4
--
To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
