Re: [Qemu-devel] [PATCH 2/7] target/mips: Add MXU instructions S32I2M and S32M2I

[Richard Henderson <richard.henderson@linaro.org>]

On 08/24/2018 12:44 PM, Craig Janeczek via Qemu-devel wrote:
> Adds support for emulating the S32I2M and S32M2I MXU instructions.
> 
> Signed-off-by: Craig Janeczek <jancraig@amazon.com>
> ---
>  target/mips/translate.c | 55 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 55 insertions(+)
> 
> diff --git a/target/mips/translate.c b/target/mips/translate.c
> index 50f0cb558f..381dfad36e 100644
> --- a/target/mips/translate.c
> +++ b/target/mips/translate.c
> @@ -364,6 +364,9 @@ enum {
>      OPC_CLO      = 0x21 | OPC_SPECIAL2,
>      OPC_DCLZ     = 0x24 | OPC_SPECIAL2,
>      OPC_DCLO     = 0x25 | OPC_SPECIAL2,
> +    /* MXU */
> +    OPC_MXU_S32I2M = 0x2F | OPC_SPECIAL2,
> +    OPC_MXU_S32M2I = 0x2E | OPC_SPECIAL2,

I haven't been able to find any documentation of the bit
layout of these instructions.  Any pointers?

> +typedef union {
> +    struct {
> +        uint32_t op:6;
> +        uint32_t xra:5;
> +        uint32_t:5;
> +        uint32_t rb:5;
> +        uint32_t:5;
> +        uint32_t special2:6;
> +    } S32I2M;
> +
> +    struct {
> +        uint32_t op:6;
> +        uint32_t xra:5;
> +        uint32_t:5;
> +        uint32_t rb:5;
> +        uint32_t:5;
> +        uint32_t special2:6;
> +    } S32M2I;
> +} MXU_OPCODE;

Do not use bitfields.  The layout differs by host compiler.
Use extract32(input, pos, len).


> +
> +/* MXU Instructions */
> +static void gen_mxu(DisasContext *ctx, uint32_t opc)
> +{
> +#ifndef TARGET_MIPS64 /* Only works in 32 bit mode */
> +    TCGv t0;
> +    t0 = tcg_temp_new();
> +    MXU_OPCODE *opcode = (MXU_OPCODE *)&ctx->opcode;
> +
> +    switch (opc) {
> +    case OPC_MXU_S32I2M:
> +        gen_load_gpr(t0, opcode->S32I2M.rb);
> +        gen_store_mxu_gpr(t0, opcode->S32I2M.xra);
> +        break;
> +
> +    case OPC_MXU_S32M2I:
> +        gen_load_mxu_gpr(t0, opcode->S32M2I.xra);
> +        gen_store_gpr(t0, opcode->S32M2I.rb);
> +        break;
> +    }
> +
> +    tcg_temp_free(t0);
> +#else
> +    generate_exception_end(ctx, EXCP_RI);
> +#endif
> +}

There's nothing here (yet, I suppose) that won't compile for MIPS64.
I'd suggest avoiding ifdefs as much as possible.


r~