@@ -1146,10 +1146,10 @@ static uint64_t NAME(uint64_t n, uint64_t m, uint64_t a, uint8_t p, bool neg) \
uint64_t sum = 0; \
/* Apply P to N as a mask, making the inactive elements 0. */ \
n &= expand_pred_h(p); \
- sum += (NTYPE)(n >> 0) * (MTYPE)(m >> 0); \
- sum += (NTYPE)(n >> 16) * (MTYPE)(m >> 16); \
- sum += (NTYPE)(n >> 32) * (MTYPE)(m >> 32); \
- sum += (NTYPE)(n >> 48) * (MTYPE)(m >> 48); \
+ sum += (int64_t)(NTYPE)(n >> 0) * (MTYPE)(m >> 0); \
+ sum += (int64_t)(NTYPE)(n >> 16) * (MTYPE)(m >> 16); \
+ sum += (int64_t)(NTYPE)(n >> 32) * (MTYPE)(m >> 32); \
+ sum += (int64_t)(NTYPE)(n >> 48) * (MTYPE)(m >> 48); \
return neg ? a - sum : a + sum; \
}
The UMOPA/UMOPS instructions are supposed to multiply unsigned 8 or 16 bit elements and accumulate the products into a 64-bit element. In the Arm ARM pseudocode, this is done with the usual infinite-precision signed arithmetic. However our implementation doesn't quite get it right, because in the DEF_IMOP_64() macro we do: sum += (NTYPE)(n >> 0) * (MTYPE)(m >> 0); where NTYPE and MTYPE are uint16_t or int16_t. In the uint16_t case, the C usual arithmetic conversions mean the values are converted to "int" type and the multiply is done as a 32-bit multiply. This means that if the inputs are, for example, 0xffff and 0xffff then the result is 0xFFFE0001 as an int, which is then promoted to uint64_t for the accumulation into sum; this promotion incorrectly sign extends the multiply. Avoid the incorrect sign extension by casting to int64_t before the multiply, so we do the multiply as 64-bit signed arithmetic, which is a type large enough that the multiply can never overflow into the sign bit. (The equivalent 8-bit operations in DEF_IMOP_32() are fine, because the 8-bit multiplies can never overflow into the sign bit of a 32-bit integer.) Cc: qemu-stable@nongnu.org Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2372 Signed-off-by: Peter Maydell <peter.maydell@linaro.org> --- target/arm/tcg/sme_helper.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)