Re: [Qemu-ppc] [PATCH 08/19] target/ppc: Fix nip on power management instructions

[Cédric Le Goater]

On 2/13/19 1:04 AM, Benjamin Herrenschmidt wrote:
> On Tue, 2019-02-12 at 17:02 +1100, David Gibson wrote:
>> On Mon, Jan 28, 2019 at 10:46:14AM +0100, Cédric Le Goater wrote:
>>> From: Benjamin Herrenschmidt <address@hidden>
>>>
>>> Those instructions currently raise an exception from within
>>> the helper. This tends to result in a bogus nip value in
>>> the env context (typically the beginning of the TB). Such
>>> a helper needs a gen_update_nip() first.
>>>
>>> This fixes it with a different approach which is to throw
>>> the exception from translate.c instead of the helper using
>>> gen_exception_nip() which does the right thing.
>>>
>>> Signed-off-by: Benjamin Herrenschmidt <address@hidden>
>>> Signed-off-by: Cédric Le Goater <address@hidden>
>>> ---
>>>  target/ppc/excp_helper.c |  1 -
>>>  target/ppc/translate.c   | 12 ++++++++----
>>>  2 files changed, 8 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
>>> index 751d759fcc1d..8407e0ade938 100644
>>> --- a/target/ppc/excp_helper.c
>>> +++ b/target/ppc/excp_helper.c
>>> @@ -958,7 +958,6 @@ void helper_pminsn(CPUPPCState *env, powerpc_pm_insn_t 
>>> insn)
>>>       * but this doesn't seem to be a problem.
>>>       */
>>>      env->msr |= (1ull << MSR_EE);
>>> -    raise_exception(env, EXCP_HLT);
>>>  }
>>>  #endif /* defined(TARGET_PPC64) */
>>>  
>>> diff --git a/target/ppc/translate.c b/target/ppc/translate.c
>>> index 7d40a1fbe6bd..55281a8975e0 100644
>>> --- a/target/ppc/translate.c
>>> +++ b/target/ppc/translate.c
>>> @@ -3571,7 +3571,8 @@ static void gen_doze(DisasContext *ctx)
>>>      t = tcg_const_i32(PPC_PM_DOZE);
>>>      gen_helper_pminsn(cpu_env, t);
>>>      tcg_temp_free_i32(t);
>>> -    gen_stop_exception(ctx);
>>> +    /* Stop translation, as the CPU is supposed to sleep from now */
>>> +    gen_exception_nip(ctx, EXCP_HLT, ctx->base.pc_next);
>>
>> IIUC this also changes from EXCP_STOP to EXCP_HLT, is that intentional?
> 
> Off the top of my head, it might be to break out of the outer exec
> loop, but I don't remember off hand.

yes and POWERPC_EXCP_STOP is only used under linux-user, which is the 
wrong value to exit from the cpu exec loop.

I think this is correct.

C. 
 

>>>  #endif /* defined(CONFIG_USER_ONLY) */
>>>  }
>>>  
>>> @@ -3586,7 +3587,8 @@ static void gen_nap(DisasContext *ctx)
>>>      t = tcg_const_i32(PPC_PM_NAP);
>>>      gen_helper_pminsn(cpu_env, t);
>>>      tcg_temp_free_i32(t);
>>> -    gen_stop_exception(ctx);
>>> +    /* Stop translation, as the CPU is supposed to sleep from now */
>>> +    gen_exception_nip(ctx, EXCP_HLT, ctx->base.pc_next);
>>>  #endif /* defined(CONFIG_USER_ONLY) */
>>>  }
>>>  
>>> @@ -3606,7 +3608,8 @@ static void gen_sleep(DisasContext *ctx)
>>>      t = tcg_const_i32(PPC_PM_SLEEP);
>>>      gen_helper_pminsn(cpu_env, t);
>>>      tcg_temp_free_i32(t);
>>> -    gen_stop_exception(ctx);
>>> +    /* Stop translation, as the CPU is supposed to sleep from now */
>>> +    gen_exception_nip(ctx, EXCP_HLT, ctx->base.pc_next);
>>>  #endif /* defined(CONFIG_USER_ONLY) */
>>>  }
>>>  
>>> @@ -3621,7 +3624,8 @@ static void gen_rvwinkle(DisasContext *ctx)
>>>      t = tcg_const_i32(PPC_PM_RVWINKLE);
>>>      gen_helper_pminsn(cpu_env, t);
>>>      tcg_temp_free_i32(t);
>>> -    gen_stop_exception(ctx);
>>> +    /* Stop translation, as the CPU is supposed to sleep from now */
>>> +    gen_exception_nip(ctx, EXCP_HLT, ctx->base.pc_next);
>>>  #endif /* defined(CONFIG_USER_ONLY) */
>>>  }
>>>  #endif /* #if defined(TARGET_PPC64) */
>