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[PATCH 2/3] accel/tcg: Fix overwrite problems of tcg_cflags

Richard Henderson posted 3 patches 2 years, 10 months ago
There is a newer version of this series
[PATCH 2/3] accel/tcg: Fix overwrite problems of tcg_cflags
Posted by Richard Henderson 2 years, 10 months ago 
From: Weiwei Li <liweiwei@iscas.ac.cn>

CPUs often set CF_PCREL in tcg_cflags before qemu_init_vcpu(), in which
tcg_cflags will be overwrited by tcg_cpu_init_cflags().

Fixes: 4be790263ffc ("accel/tcg: Replace `TARGET_TB_PCREL` with `CF_PCREL`")
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Message-Id: <20230331150609.114401-6-liweiwei@iscas.ac.cn>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 accel/tcg/tcg-accel-ops.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/accel/tcg/tcg-accel-ops.c b/accel/tcg/tcg-accel-ops.c
index af35e0d092..58c8e64096 100644
--- a/accel/tcg/tcg-accel-ops.c
+++ b/accel/tcg/tcg-accel-ops.c
@@ -59,7 +59,7 @@ void tcg_cpu_init_cflags(CPUState *cpu, bool parallel)
 
     cflags |= parallel ? CF_PARALLEL : 0;
     cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
-    cpu->tcg_cflags = cflags;
+    cpu->tcg_cflags |= cflags;
 }
 
 void tcg_cpus_destroy(CPUState *cpu)
-- 
2.34.1
Re: [PATCH 2/3] accel/tcg: Fix overwrite problems of tcg_cflags
Posted by Philippe Mathieu-Daudé 2 years, 10 months ago 
On 1/4/23 06:51, Richard Henderson wrote:
> From: Weiwei Li <liweiwei@iscas.ac.cn>
> 
> CPUs often set CF_PCREL in tcg_cflags before qemu_init_vcpu(), in which
> tcg_cflags will be overwrited by tcg_cpu_init_cflags().

The description makes sense, but I couldn't reproduce using:

-- >8 --
diff --git a/accel/tcg/tcg-accel-ops.c b/accel/tcg/tcg-accel-ops.c
index af35e0d092..23ebf7de21 100644
--- a/accel/tcg/tcg-accel-ops.c
+++ b/accel/tcg/tcg-accel-ops.c
@@ -59,6 +59,7 @@ void tcg_cpu_init_cflags(CPUState *cpu, bool parallel)

      cflags |= parallel ? CF_PARALLEL : 0;
      cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
+    tcg_debug_assert(!cpu->tcg_cflags);
      cpu->tcg_cflags = cflags;
  }
---

Li and Junqiang, what is your use case?

> Fixes: 4be790263ffc ("accel/tcg: Replace `TARGET_TB_PCREL` with `CF_PCREL`")
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
> Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
> Message-Id: <20230331150609.114401-6-liweiwei@iscas.ac.cn>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   accel/tcg/tcg-accel-ops.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/accel/tcg/tcg-accel-ops.c b/accel/tcg/tcg-accel-ops.c
> index af35e0d092..58c8e64096 100644
> --- a/accel/tcg/tcg-accel-ops.c
> +++ b/accel/tcg/tcg-accel-ops.c
> @@ -59,7 +59,7 @@ void tcg_cpu_init_cflags(CPUState *cpu, bool parallel)
>   
>       cflags |= parallel ? CF_PARALLEL : 0;
>       cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
> -    cpu->tcg_cflags = cflags;
> +    cpu->tcg_cflags |= cflags;

This could be acceptable as a release kludge, but semantically
tcg_cpu_init_cflags() is meant to *initialize* all flags, not
set few of them. Either we aren't calling it from the proper place,
or we need to rename it.

>   }
>   
>   void tcg_cpus_destroy(CPUState *cpu)
Re: [PATCH 2/3] accel/tcg: Fix overwrite problems of tcg_cflags
Posted by liweiwei 2 years, 10 months ago 
On 2023/4/3 16:09, Philippe Mathieu-Daudé wrote:
> On 1/4/23 06:51, Richard Henderson wrote:
>> From: Weiwei Li <liweiwei@iscas.ac.cn>
>>
>> CPUs often set CF_PCREL in tcg_cflags before qemu_init_vcpu(), in which
>> tcg_cflags will be overwrited by tcg_cpu_init_cflags().
>
> The description makes sense, but I couldn't reproduce using:
>
> -- >8 --
> diff --git a/accel/tcg/tcg-accel-ops.c b/accel/tcg/tcg-accel-ops.c
> index af35e0d092..23ebf7de21 100644
> --- a/accel/tcg/tcg-accel-ops.c
> +++ b/accel/tcg/tcg-accel-ops.c
> @@ -59,6 +59,7 @@ void tcg_cpu_init_cflags(CPUState *cpu, bool parallel)
>
>      cflags |= parallel ? CF_PARALLEL : 0;
>      cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
> +    tcg_debug_assert(!cpu->tcg_cflags);
>      cpu->tcg_cflags = cflags;
>  }
> ---
>
> Li and Junqiang, what is your use case?

Only few CPUs support CF_PCREL currently. I found this problem when I 
tried to introduce PC-relative translation into RISC-V.

Maybe It also can be reproduced in system mode for ARM and X86.

Regards,

Weiwei Li


>
>> Fixes: 4be790263ffc ("accel/tcg: Replace `TARGET_TB_PCREL` with 
>> `CF_PCREL`")
>> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>> Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
>> Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
>> Message-Id: <20230331150609.114401-6-liweiwei@iscas.ac.cn>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>   accel/tcg/tcg-accel-ops.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/accel/tcg/tcg-accel-ops.c b/accel/tcg/tcg-accel-ops.c
>> index af35e0d092..58c8e64096 100644
>> --- a/accel/tcg/tcg-accel-ops.c
>> +++ b/accel/tcg/tcg-accel-ops.c
>> @@ -59,7 +59,7 @@ void tcg_cpu_init_cflags(CPUState *cpu, bool parallel)
>>         cflags |= parallel ? CF_PARALLEL : 0;
>>       cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
>> -    cpu->tcg_cflags = cflags;
>> +    cpu->tcg_cflags |= cflags;
>
> This could be acceptable as a release kludge, but semantically
> tcg_cpu_init_cflags() is meant to *initialize* all flags, not
> set few of them. Either we aren't calling it from the proper place,
> or we need to rename it.
>
>>   }
>>     void tcg_cpus_destroy(CPUState *cpu)
Re: [PATCH 2/3] accel/tcg: Fix overwrite problems of tcg_cflags
Posted by Anton Johansson via 2 years, 10 months ago 
On 4/3/23 11:09, liweiwei wrote:
>
> On 2023/4/3 16:09, Philippe Mathieu-Daudé wrote:
>>      cflags |= parallel ? CF_PARALLEL : 0;
>>      cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
>> +    tcg_debug_assert(!cpu->tcg_cflags);
>>      cpu->tcg_cflags = cflags;
>>  }
>> ---
>>
>> Li and Junqiang, what is your use case?
>
> Only few CPUs support CF_PCREL currently. I found this problem when I 
> tried to introduce PC-relative translation into RISC-V.
>
> Maybe It also can be reproduced in system mode for ARM and X86.

Yes, this can be reproduced on arm-softmmu with --enable-debug-tcg and 
the above assertion.


On 4/3/23 10:09, Philippe Mathieu-Daudé wrote:
>>
>> diff --git a/accel/tcg/tcg-accel-ops.c b/accel/tcg/tcg-accel-ops.c
>> index af35e0d092..58c8e64096 100644
>> --- a/accel/tcg/tcg-accel-ops.c
>> +++ b/accel/tcg/tcg-accel-ops.c
>> @@ -59,7 +59,7 @@ void tcg_cpu_init_cflags(CPUState *cpu, bool parallel)
>>         cflags |= parallel ? CF_PARALLEL : 0;
>>       cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
>> -    cpu->tcg_cflags = cflags;
>> +    cpu->tcg_cflags |= cflags;
>
> This could be acceptable as a release kludge, but semantically
> tcg_cpu_init_cflags() is meant to *initialize* all flags, not
> set few of them. Either we aren't calling it from the proper place,
> or we need to rename it.
Agree, this sounds reasonable.  Also, maybe setting
cpu->tcg_cflags from *_cpu_realizefn was not the right call and
we should have some other way of providing target specific cflags.

-- 
Anton Johansson,
rev.ng Labs Srl.
Re: [PATCH 2/3] accel/tcg: Fix overwrite problems of tcg_cflags
Posted by Philippe Mathieu-Daudé 2 years, 10 months ago 
On 3/4/23 12:44, Anton Johansson wrote:
> 
> On 4/3/23 11:09, liweiwei wrote:
>>
>> On 2023/4/3 16:09, Philippe Mathieu-Daudé wrote:
>>>      cflags |= parallel ? CF_PARALLEL : 0;
>>>      cflags |= icount_enabled() ? CF_USE_ICOUNT : 0;
>>> +    tcg_debug_assert(!cpu->tcg_cflags);
>>>      cpu->tcg_cflags = cflags;
>>>  }
>>> ---
>>>
>>> Li and Junqiang, what is your use case?
>>
>> Only few CPUs support CF_PCREL currently. I found this problem when I 
>> tried to introduce PC-relative translation into RISC-V.
>>
>> Maybe It also can be reproduced in system mode for ARM and X86.
> 
> Yes, this can be reproduced on arm-softmmu with --enable-debug-tcg and 
> the above assertion.

Ah OK. Then...

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Patchew 2.1-devel-b67e4c2

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