Re: [RFC PATCH 09/13] cpus: Add const-qualified CPU environment accessors

On 2026-08-20 17:21, Richard Henderson wrote:
> On 8/20/26 03:47, Philippe Mathieu-Daudé wrote:
>> Introduce const-qualified variants of cpu_env() and
>> env_archcpu(), to safely access CPU architecture
>> state when it should not be modified.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
>> ---
>>   include/exec/cpu-common.h | 11 +++++++++++
>>   include/hw/core/cpu.h     |  6 ++++++
>>   2 files changed, 17 insertions(+)
>>
>> diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
>> index 6594f7fa1be..f3a3799f451 100644
>> --- a/include/exec/cpu-common.h
>> +++ b/include/exec/cpu-common.h
>> @@ -79,6 +79,17 @@ static inline bool cpu_loop_exit_requested(const 
>> CPUState *cpu)
>>   }
>>   #endif /* CONFIG_TCG */
>> +/**
>> + * env_archcpu_const(env)
>> + * @env: The architecture environment (const).
>> + *
>> + * Return the const ArchCPU associated with the environment.
>> + */
>> +static inline const ArchCPU *env_archcpu_const(const CPUArchState *env)
>> +{
>> +    return (const void *)env - sizeof(CPUState);
>> +}
>> +
>>   /**
>>    * env_archcpu(env)
>>    * @env: The architecture environment
>> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
>> index 81af7b9ee1a..59f777f3f15 100644
>> --- a/include/hw/core/cpu.h
>> +++ b/include/hw/core/cpu.h
>> @@ -594,6 +594,12 @@ struct CPUState {
>>   QEMU_BUILD_BUG_ON(offsetof(CPUState, neg) !=
>>                     sizeof(CPUState) - sizeof(CPUNegativeOffsetState));
>> +static inline const CPUArchState *cpu_env_const(const CPUState *cpu)
>> +{
>> +    /* We validate that CPUArchState follows CPUState in cpu-target.c */
>> +    return (const CPUArchState *)(cpu + 1);
>> +}
>> +
>>   static inline CPUArchState *cpu_env(CPUState *cpu)
>>   {
>>       /* We validate that CPUArchState follows CPUState in cpu- 
>> target.c */
> 
> I wonder if we can use _Generic to make this automatic, rather than have 
> to choose between two different function names.
Eh clever :) This seems to work:

   #define env_archcpu_(p) _Generic(*(p), \
                               CPUArchState: (void *)p, \
                               const CPUArchState: (const void *)p)