Re: [Qemu-devel] [PATCH v1] target/s390x: Add support for the TEST BLOCK instruction

[Aurelien Jarno]

On 2017-05-16 11:28, Thomas Huth wrote:
> TEST BLOCK was likely once used to execute basic memory
> tests, but nowadays it's just a (slow) way to clear a page.
> 
> Signed-off-by: Thomas Huth <address@hidden>
> ---
>  target/s390x/helper.h      |  1 +
>  target/s390x/insn-data.def |  2 ++
>  target/s390x/mem_helper.c  | 12 ++++++++++++
>  target/s390x/translate.c   | 10 ++++++++++
>  4 files changed, 25 insertions(+)
> 
> diff --git a/target/s390x/helper.h b/target/s390x/helper.h
> index 9102071..a5a3705 100644
> --- a/target/s390x/helper.h
> +++ b/target/s390x/helper.h
> @@ -99,6 +99,7 @@ DEF_HELPER_FLAGS_4(lctl, TCG_CALL_NO_WG, void, env, i32, 
> i64, i32)
>  DEF_HELPER_FLAGS_4(lctlg, TCG_CALL_NO_WG, void, env, i32, i64, i32)
>  DEF_HELPER_FLAGS_4(stctl, TCG_CALL_NO_WG, void, env, i32, i64, i32)
>  DEF_HELPER_FLAGS_4(stctg, TCG_CALL_NO_WG, void, env, i32, i64, i32)
> +DEF_HELPER_2(testblock, void, env, i64)
>  DEF_HELPER_FLAGS_2(tprot, TCG_CALL_NO_RWG, i32, i64, i64)
>  DEF_HELPER_FLAGS_2(iske, TCG_CALL_NO_RWG_SE, i64, env, i64)
>  DEF_HELPER_FLAGS_3(sske, TCG_CALL_NO_RWG, void, env, i64, i64)
> diff --git a/target/s390x/insn-data.def b/target/s390x/insn-data.def
> index 075ff59..a6aba54 100644
> --- a/target/s390x/insn-data.def
> +++ b/target/s390x/insn-data.def
> @@ -912,6 +912,8 @@
>  /* STORE USING REAL ADDRESS */
>      C(0xb246, STURA,   RRE,   Z,   r1_o, r2_o, 0, 0, stura, 0)
>      C(0xb925, STURG,   RRE,   Z,   r1_o, r2_o, 0, 0, sturg, 0)
> +/* TEST BLOCK */
> +    C(0xb22c, TB,      RRE,   Z,   0, r2_o, 0, 0, testblock, 0)
>  /* TEST PROTECTION */
>      C(0xe501, TPROT,   SSE,   Z,   la1, a2, 0, 0, tprot, 0)
>  
> diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
> index 675aba2..0349c10 100644
> --- a/target/s390x/mem_helper.c
> +++ b/target/s390x/mem_helper.c
> @@ -933,6 +933,18 @@ void HELPER(stctl)(CPUS390XState *env, uint32_t r1, 
> uint64_t a2, uint32_t r3)
>      }
>  }
>  
> +void HELPER(testblock)(CPUS390XState *env, uint64_t addr)
> +{
> +    CPUState *cs = CPU(s390_env_get_cpu(env));
> +    int i;
> +
> +    addr = get_address(env, 0, 0, addr) & ~0xfffULL;

I guess you want to use ~TARGET_PAGE_MASK here.

> +    for (i = 0; i < TARGET_PAGE_SIZE; i += 8) {
> +        stq_phys(cs->as, addr + i, 0);
> +    }
> +    env->cc_op = 0;
> +}
> +

From what I understand the resulting condition code should depends if
the block is usable or not. Shouldn't there be a check to see if the
address actually targets the RAM?

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
address@hidden                 http://www.aurel32.net