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

On 2026-08-20 18:24, Philippe Mathieu-Daudé wrote:
> 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)

Actually simpler and even well readable:

-- >8 --
diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index 6594f7fa1b..d67d008236 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -85,21 +85,11 @@ static inline bool cpu_loop_exit_requested(const 
CPUState *cpu)
   *
   * Return the ArchCPU associated with the environment.
   */
-static inline ArchCPU *env_archcpu(CPUArchState *env)
-{
-    return (void *)env - sizeof(CPUState);
-}
-
-/**
- * env_cpu_const(env)
- * @env: The architecture environment
- *
- * Return the CPUState associated with the environment.
- */
-static inline const CPUState *env_cpu_const(const CPUArchState *env)
-{
-    return (void *)env - sizeof(CPUState);
-}
+#define env_archcpu(env) _Generic(*(env), \
+            CPUArchState: \
+                (ArchCPU *)((void *)env - sizeof(CPUState)), \
+            const CPUArchState: \
+                (const ArchCPU *)((const void *)env - sizeof(CPUState)))

  /**
   * env_cpu(env)
@@ -107,9 +97,10 @@ static inline const CPUState *env_cpu_const(const 
CPUArchState *env)
   *
   * Return the CPUState associated with the environment.
   */
-static inline CPUState *env_cpu(CPUArchState *env)
-{
-    return (CPUState *)env_cpu_const(env);
-}
+#define env_cpu(env) _Generic(*(env), \
+            CPUArchState: \
+                (CPUState *)((void *)env - sizeof(CPUState)), \
+            const CPUArchState: \
+                (const CPUState *)((const void *)env - sizeof(CPUState)))

  #endif /* CPU_COMMON_H */
---