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List:       qemu-s390x
Subject:    Re: [PATCH v4 3/5] target/s390x: Fix cc_calc_sla_64() missing overflows
From:       David Hildenbrand <david () redhat ! com>
Date:       2022-01-13 8:21:38
Message-ID: 0a9642a1-7f36-12a8-1f83-0016a493e907 () redhat ! com
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On 12.01.22 17:50, Ilya Leoshkevich wrote:
> An overflow occurs for SLAG when at least one shifted bit is not equal
> to sign bit. Therefore, we need to check that `shift + 1` bits are
> neither all 0s nor all 1s. The current code checks only `shift` bits,
> missing some overflows.
> 
> Fixes: cbe24bfa91d2 ("target-s390: Convert SHIFT, ROTATE SINGLE")
> Co-developed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  target/s390x/tcg/cc_helper.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target/s390x/tcg/cc_helper.c b/target/s390x/tcg/cc_helper.c
> index c2c96c3a3c..c9b7b0e8c6 100644
> --- a/target/s390x/tcg/cc_helper.c
> +++ b/target/s390x/tcg/cc_helper.c
> @@ -297,7 +297,7 @@ static uint32_t cc_calc_sla_32(uint32_t src, int shift)
>  
>  static uint32_t cc_calc_sla_64(uint64_t src, int shift)
>  {
> -    uint64_t mask = ((1ULL << shift) - 1ULL) << (64 - shift);
> +    uint64_t mask = -1ULL << (63 - shift);
>      uint64_t sign = 1ULL << 63;
>      uint64_t match;
>      int64_t r;

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb


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