[v1] target/riscv: Fix shift count overflow

[PATCH] target/riscv: Fix shift count overflow

demin.han posted 1 patch 9 months ago

Diff against v2 v3
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git fetch https://github.com/patchew-project/qemu tags/patchew/20240224130235.340584-1-demin.han@starfivetech.com

Maintainers: Palmer Dabbelt <palmer@dabbelt.com>, Alistair Francis <alistair.francis@wdc.com>, Bin Meng <bin.meng@windriver.com>, Weiwei Li <liwei1518@gmail.com>, Daniel Henrique Barboza <dbarboza@ventanamicro.com>, Liu Zhiwei <zhiwei_liu@linux.alibaba.com>

There is a newer version of this series

target/riscv/vector_helper.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

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[PATCH] target/riscv: Fix shift count overflow

Posted by demin.han 9 months ago

The result of (8 - 3 - vlmul) is negtive when vlmul >= 6,
and results in wrong vill.

Signed-off-by: demin.han <demin.han@starfivetech.com>
---
 target/riscv/vector_helper.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
index 84cec73eb2..ced0aca633 100644
--- a/target/riscv/vector_helper.c
+++ b/target/riscv/vector_helper.c
@@ -53,10 +53,9 @@ target_ulong HELPER(vsetvl)(CPURISCVState *env, target_ulong s1,
          * VLEN * LMUL >= SEW
          * VLEN >> (8 - lmul) >= sew
          * (vlenb << 3) >> (8 - lmul) >= sew
-         * vlenb >> (8 - 3 - lmul) >= sew
          */
         if (vlmul == 4 ||
-            cpu->cfg.vlenb >> (8 - 3 - vlmul) < sew) {
+            (cpu->cfg.vlenb << 3) >> (8 - vlmul) < sew) {
             vill = true;
         }
     }
-- 
2.43.2

Re: [PATCH] target/riscv: Fix shift count overflow

Posted by Daniel Henrique Barboza 9 months ago


On 2/24/24 10:02, demin.han wrote:
> The result of (8 - 3 - vlmul) is negtive when vlmul >= 6,
> and results in wrong vill.
> 
> Signed-off-by: demin.han <demin.han@starfivetech.com>
> ---
>   target/riscv/vector_helper.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
> index 84cec73eb2..ced0aca633 100644
> --- a/target/riscv/vector_helper.c
> +++ b/target/riscv/vector_helper.c
> @@ -53,10 +53,9 @@ target_ulong HELPER(vsetvl)(CPURISCVState *env, target_ulong s1,
>            * VLEN * LMUL >= SEW
>            * VLEN >> (8 - lmul) >= sew
>            * (vlenb << 3) >> (8 - lmul) >= sew
> -         * vlenb >> (8 - 3 - lmul) >= sew
>            */
>           if (vlmul == 4 ||
> -            cpu->cfg.vlenb >> (8 - 3 - vlmul) < sew) {
> +            (cpu->cfg.vlenb << 3) >> (8 - vlmul) < sew) {
>               vill = true;
>           }

Please add a new var:

uint16_t vlen = cpu->cfg.vlenb << 3;

And use it in the 'if' to be more readable:

            if (vlmul == 4 ||
                vlen >> (8 - 3 - vlmul) < sew) {
                vill = true;
            }


Thanks,

Daniel


>       }