Re: [Qemu-arm] [PATCH 2/2] target/arm/translate-a64: Fix mishandling of size in FCMLA decode

[Laurent Desnogues]

On Tue, Jan 29, 2019 at 3:04 PM Peter Maydell <address@hidden> wrote:
>
> In disas_simd_indexed(), for the case of "complex fp", each indexable
> element is a complex pair, so the total size is twice that indicated
> in the 'size' field in the encoding. We were trying to do this
> "double the size" operation with a left shift by 1, but this is
> incorrect because the 'size' field is a MO_8/MO_16/MO_32/MO_64
> value, and doubling the size should be done by a simple increment.
>
> This meant we were mishandling FCMLA (by element) of values where
> the real and imaginary parts are 32-bit floats, and would incorrectly
> UNDEF this encoding. (No other insns take this code path, and for
> 16-bit floats it happens that 1 << 1 and 1 + 1 are both the same).
>
> Reported-by: Laurent Desnogues <address@hidden>
> Signed-off-by: Peter Maydell <address@hidden>

Reviewed-by: Laurent Desnogues <address@hidden>

Thanks,

Laurent

> ---
>  target/arm/translate-a64.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
> index a7b999d2b5a..06418f0ac3c 100644
> --- a/target/arm/translate-a64.c
> +++ b/target/arm/translate-a64.c
> @@ -12680,7 +12680,7 @@ static void disas_simd_indexed(DisasContext *s, 
> uint32_t insn)
>
>      case 2: /* complex fp */
>          /* Each indexable element is a complex pair.  */
> -        size <<= 1;
> +        size += 1;
>          switch (size) {
>          case MO_32:
>              if (h && !is_q) {
> --
> 2.20.1
>