Re: [Qemu-devel] [PATCH RESEND v2 11/17] target-ppc: implement darn instruction

[David Gibson]

On Mon, Sep 12, 2016 at 12:11:40PM +0530, Nikunj A Dadhania wrote:
> From: Ravi Bangoria <address@hidden>
> 
> darn: Deliver A Random Number
> 
> Currently return invalid random number for all the case. This needs
> proper algorithm to provide cryptographically suitable random data.
> Reading from /dev/random can block and that is not an expected behaviour
> while the cpu instruction is getting executed. Moreover, /dev/random
> would only work for linux-user
> 
> Signed-off-by: Ravi Bangoria <address@hidden>
> Signed-off-by: Nikunj A Dadhania <address@hidden>
> ---
>  target-ppc/helper.h     |  2 ++
>  target-ppc/int_helper.c | 16 ++++++++++++++++
>  target-ppc/translate.c  | 18 ++++++++++++++++++
>  3 files changed, 36 insertions(+)
> 
> diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> index e75d070..966f2ce 100644
> --- a/target-ppc/helper.h
> +++ b/target-ppc/helper.h
> @@ -50,6 +50,8 @@ DEF_HELPER_FLAGS_1(cnttzd, TCG_CALL_NO_RWG_SE, tl, tl)
>  DEF_HELPER_FLAGS_1(popcntd, TCG_CALL_NO_RWG_SE, tl, tl)
>  DEF_HELPER_FLAGS_2(bpermd, TCG_CALL_NO_RWG_SE, i64, i64, i64)
>  DEF_HELPER_3(srad, tl, env, tl, tl)
> +DEF_HELPER_0(darn32, tl)
> +DEF_HELPER_0(darn64, tl)
>  #endif
>  
>  DEF_HELPER_FLAGS_1(cntlsw32, TCG_CALL_NO_RWG_SE, i32, i32)
> diff --git a/target-ppc/int_helper.c b/target-ppc/int_helper.c
> index 291fba0..51a9ac5 100644
> --- a/target-ppc/int_helper.c
> +++ b/target-ppc/int_helper.c
> @@ -182,6 +182,22 @@ target_ulong helper_cnttzd(target_ulong t)
>  {
>      return ctz64(t);
>  }
> +
> +/* Return invalid random number.
> + *
> + * FIXME: Add rng backend or other mechanism to get cryptographically 
> suitable
> + * random number
> + */
> +target_ulong helper_darn32(void)
> +{
> +    return -1;
> +}
> +
> +target_ulong helper_darn64(void)
> +{
> +    return -1;
> +}
> +

TBH, I think you're going to want a single helper for both 32-bit and
64-bit cases.

>  #endif
>  
>  #if defined(TARGET_PPC64)
> diff --git a/target-ppc/translate.c b/target-ppc/translate.c
> index 133c531..e9dad3f 100644
> --- a/target-ppc/translate.c
> +++ b/target-ppc/translate.c
> @@ -528,6 +528,8 @@ EXTRACT_HELPER(FPW, 16, 1);
>  
>  /* addpcis */
>  EXTRACT_HELPER_DXFORM(DX, 10, 6, 6, 5, 16, 1, 1, 0, 0)
> +/* darn */
> +EXTRACT_HELPER(L, 16, 2);
>  
>  /***                            Jump target decoding                       
> ***/
>  /* Immediate address */
> @@ -1895,6 +1897,21 @@ static void gen_cnttzd(DisasContext *ctx)
>          gen_set_Rc0(ctx, cpu_gpr[rA(ctx->opcode)]);
>      }
>  }
> +
> +/* darn */
> +static void gen_darn(DisasContext *ctx)
> +{
> +    int l = L(ctx->opcode);
> +
> +    if (l == 0) {
> +        gen_helper_darn32(cpu_gpr[rD(ctx->opcode)]);
> +    } else if (l <= 2) {
> +        /* Return 64-bit random for both CRN and RRN */
> +        gen_helper_darn64(cpu_gpr[rD(ctx->opcode)]);

So it might be simpler to just leave out the helper stubs for now, and
always return the invalid value from the generated code.

> +    } else {
> +        tcg_gen_movi_i64(cpu_gpr[rD(ctx->opcode)], -1);
> +    }
> +}
>  #endif
>  
>  /***                             Integer rotate                            
> ***/
> @@ -6212,6 +6229,7 @@ GEN_HANDLER_E(prtyw, 0x1F, 0x1A, 0x04, 0x0000F801, 
> PPC_NONE, PPC2_ISA205),
>  GEN_HANDLER(popcntd, 0x1F, 0x1A, 0x0F, 0x0000F801, PPC_POPCNTWD),
>  GEN_HANDLER(cntlzd, 0x1F, 0x1A, 0x01, 0x00000000, PPC_64B),
>  GEN_HANDLER_E(cnttzd, 0x1F, 0x1A, 0x11, 0x00000000, PPC_NONE, PPC2_ISA300),
> +GEN_HANDLER_E(darn, 0x1F, 0x13, 0x17, 0x001CF801, PPC_NONE, PPC2_ISA300),
>  GEN_HANDLER_E(prtyd, 0x1F, 0x1A, 0x05, 0x0000F801, PPC_NONE, PPC2_ISA205),
>  GEN_HANDLER_E(bpermd, 0x1F, 0x1C, 0x07, 0x00000001, PPC_NONE, 
> PPC2_PERM_ISA206),
>  #endif

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

signature.asc
Description: PGP signature