The cbo.* mnemonics share their opcode space with lq for those cases where
rd == 0 ("brownfield" encodings).
"Major opcode" refers to inst[6:0] according to chapter 26.
In overlapping multi-group syntax, this would look like:
> {
>
> # *** RV32 Zicbom Standard Extension ***
>
> cbo_clean 0000000 00001 ..... 010 00000 0001111 @sfence_vm
>
> cbo_flush 0000000 00010 ..... 010 00000 0001111 @sfence_vm
>
> cbo_inval 0000000 00000 ..... 010 00000 0001111 @sfence_vm
>
>
> # *** RV32 Zicboz Standard Extension ***
>
> cbo_zero 0000000 00100 ..... 010 00000 0001111 @sfence_vm
>
>
> # *** RVI128 lq ***
>
> lq ............ ..... 010 ..... 0001111 @i
>
> }
>
Instead of using a multigroup here, I would recommend that you take a look
at https://patchwork.kernel.org/project/qemu-devel/list/?series=605340
where we have added a table of optional decoders — this could be used to
split these off into separate decoders that are run before the regular
decoder, if & only if Zicboc and/or Zicboz are enabled.
Cheers,
Philipp.
On Tue, 18 Jan 2022 at 17:32, Christoph Muellner <cmuell...@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 <cmuell...@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
>
>
