Re: [RFC PATCH v2 01/20] migration/vmstate: Restrict vmstate_dummy to user-mode

[Philippe Mathieu-Daudé]

On 1/19/21 2:50 PM, Peter Maydell wrote:
> On Sun, 17 Jan 2021 at 19:24, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>>
>> 'vmstate_dummy' is special and only used for user-mode. Rename
>> it to something more specific.
>> It was introduced restricted to user-mode in commit c71c3e99b8
>> ("Add a vmstate_dummy struct for CONFIG_USER_ONLY") but this
>> restriction was later removed in commit 6afc14e92ac ("migration:
>> Fix warning caused by missing declaration of vmstate_dummy").
>> Avoid the missing declaration warning by adding a stub for the
>> symbol, and restore the #ifdef'ry.
> 
> So what is the actual use of vmstate_dummy ? I had a grep
> through and as far as I can see the points where vmstate_cpu_common
> is used are all in softmmu-only code.

No clue, maybe simply remnant from unfinished work?

> I tried this patch
> and QEMU seems to compile OK:
> 
> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index 140fa32a5e3..a827417a4d8 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -1131,8 +1131,6 @@ bool target_words_bigendian(void);
> 
>  #ifdef CONFIG_SOFTMMU
>  extern const VMStateDescription vmstate_cpu_common;
> -#else
> -#define vmstate_cpu_common vmstate_dummy
>  #endif
> 
>  #define VMSTATE_CPU() {                                                     \

Great! Maybe even restricting VMSTATE_CPU() to softmmu-only:

-- >8 --
@@ -1131,9 +1131,6 @@ bool target_words_bigendian(void);

 #ifdef CONFIG_SOFTMMU
 extern const VMStateDescription vmstate_cpu_common;
-#else
-#define vmstate_cpu_common vmstate_dummy
-#endif

 #define VMSTATE_CPU() {
     \
     .name = "parent_obj",
     \
@@ -1142,6 +1139,7 @@ extern const VMStateDescription vmstate_cpu_common;
     .flags = VMS_STRUCT,
     \
     .offset = 0,
     \
 }
+#endif

 #endif /* NEED_CPU_H */
---

I'll wait if David/Juan have any comment, else respin based
on your patch.

Thanks,

Phil.