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

On Thu, Aug 20, 2026 at 8:52 PM Philippe Mathieu-Daudé
<[email protected]> wrote:
>
> 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 */
> ---
>

lgtm too
Reviewed-by: Marc-André Lureau <[email protected]>



-- 
Marc-André Lureau