Re: [PATCH] target/riscv: fix RV128 lq encoding

[Christoph Müllner]

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On Tue, Jan 18, 2022 at 4:12 PM Christoph Muellner <cmuellner@linux.com> wrote:
>
> If LQ has func3==010 and is located in the MISC-MEM opcodes,
> then it conflicts with the CBO opcode space.
> However, since LQ is specified as: "LQ is added to the MISC-MEM major
> opcode", we have an implementation bug, because 'major opcode'
> refers to func3, which must be 111.
>
> This results in the following instruction encodings:
>
> lq        ........ ........ .111.... .0001111
> cbo_clean 00000000 0001.... .0100000 00001111
> cbo_flush 00000000 0010.... .0100000 00001111
> cbo_inval 00000000 0000.... .0100000 00001111
> cbo_zero  00000000 0100.... .0100000 00001111
>                              ^^^-func3
>                                       ^^^^^^^-opcode
>
> Signed-off-by: Christoph Muellner <cmuellner@linux.com>
> ---
>  target/riscv/insn32.decode | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
> index 5bbedc254c..d3f798ca10 100644
> --- a/target/riscv/insn32.decode
> +++ b/target/riscv/insn32.decode
> @@ -168,7 +168,7 @@ sraw     0100000 .....  ..... 101 ..... 0111011 @r
>
>  # *** RV128I Base Instruction Set (in addition to RV64I) ***
>  ldu      ............   ..... 111 ..... 0000011 @i
> -lq       ............   ..... 010 ..... 0001111 @i
> +lq       ............   ..... 111 ..... 0001111 @i
>  sq       ............   ..... 100 ..... 0100011 @s
>  addid    ............  .....  000 ..... 1011011 @i
>  sllid    000000 ......  ..... 001 ..... 1011011 @sh6
> --
> 2.34.1
>