diff options
| author | Peter Maydell <peter.maydell@linaro.org> | 2024-07-22 18:29:55 +0100 |
|---|---|---|
| committer | Michael Tokarev <mjt@tls.msk.ru> | 2024-08-28 08:37:14 +0300 |
| commit | 61541d7dfccdd2569d8726a74490f298068c9bd1 (patch) | |
| tree | 2c46bb1baf46baec10558252524f0dfec4dafdfc | |
| parent | 4ded3bba9fc8adb05325c3260cd020d34d529bb3 (diff) | |
target/arm: Fix UMOPA/UMOPS of 16-bit values
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>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20240722172957.1041231-3-peter.maydell@linaro.org
(cherry picked from commit ea3f5a90f036734522e9af3bffd77e69e9f47355)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
| -rw-r--r-- | target/arm/tcg/sme_helper.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/target/arm/tcg/sme_helper.c b/target/arm/tcg/sme_helper.c index 5a6dd76489..f9001f5213 100644 --- a/target/arm/tcg/sme_helper.c +++ b/target/arm/tcg/sme_helper.c @@ -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; \ } |