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Subject[PATCH 4.19 230/276] overflow: Fix -Wtype-limits compilation warnings
Date
[ Upstream commit dc7fe518b0493faa0af0568d6d8c2a33c00f58d0 ]

Attempt to use check_shl_overflow() with inputs of unsigned type
produces the following compilation warnings.

drivers/infiniband/hw/mlx5/qp.c: In function _set_user_rq_size_:
./include/linux/overflow.h:230:6: warning: comparison of unsigned
expression >= 0 is always true [-Wtype-limits]
_s >= 0 && _s < 8 * sizeof(*d) ? _s : 0; \
^~
drivers/infiniband/hw/mlx5/qp.c:5820:6: note: in expansion of macro _check_shl_overflow_
if (check_shl_overflow(rwq->wqe_count, rwq->wqe_shift,
&rwq->buf_size))
^~~~~~~~~~~~~~~~~~
./include/linux/overflow.h:232:26: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
(_to_shift != _s || *_d < 0 || _a < 0 || \
^
drivers/infiniband/hw/mlx5/qp.c:5820:6: note: in expansion of macro _check_shl_overflow_
if (check_shl_overflow(rwq->wqe_count, rwq->wqe_shift, &rwq->buf_size))
^~~~~~~~~~~~~~~~~~
./include/linux/overflow.h:232:36: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
(_to_shift != _s || *_d < 0 || _a < 0 || \
^
drivers/infiniband/hw/mlx5/qp.c:5820:6: note: in expansion of macro _check_shl_overflow_
if (check_shl_overflow(rwq->wqe_count, rwq->wqe_shift,&rwq->buf_size))
^~~~~~~~~~~~~~~~~~

Fixes: 0c66847793d1 ("overflow.h: Add arithmetic shift helper")
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/overflow.h | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 40b48e2133cb8..15eb85de92269 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -36,6 +36,12 @@
#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
#define type_min(T) ((T)((T)-type_max(T)-(T)1))

+/*
+ * Avoids triggering -Wtype-limits compilation warning,
+ * while using unsigned data types to check a < 0.
+ */
+#define is_non_negative(a) ((a) > 0 || (a) == 0)
+#define is_negative(a) (!(is_non_negative(a)))

#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
/*
@@ -227,10 +233,10 @@
typeof(d) _d = d; \
u64 _a_full = _a; \
unsigned int _to_shift = \
- _s >= 0 && _s < 8 * sizeof(*d) ? _s : 0; \
+ is_non_negative(_s) && _s < 8 * sizeof(*d) ? _s : 0; \
*_d = (_a_full << _to_shift); \
- (_to_shift != _s || *_d < 0 || _a < 0 || \
- (*_d >> _to_shift) != _a); \
+ (_to_shift != _s || is_negative(*_d) || is_negative(_a) || \
+ (*_d >> _to_shift) != _a); \
})

/**
--
2.20.1


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