Re: [PATCH 09/13] target/arm/cpu: define ARM_MAX_VQ once for aarch32 and aarch64

[Pierrick Bouvier <pierrick.bouvier@linaro.org>]

On 3/18/25 11:50, Philippe Mathieu-Daudé wrote:
> On 18/3/25 05:51, Pierrick Bouvier wrote:
>> This will affect zregs field for aarch32.
>> This field is used for MVE and SVE implementations. MVE implementation
>> is clipping index value to 0 or 1 for zregs[*].d[],
>> so we should not touch the rest of data in this case anyway.
> 
> We should describe why it is safe for migration.
> 
> I.e. vmstate_za depends on za_needed() -> SME, not included in 32-bit
> cpus, etc.
> 
> Should we update target/arm/machine.c in this same patch, or a
> preliminary one?
> 

vmstate_za definition and inclusion in vmstate_arm_cpu is under #ifdef 
TARGET_AARCH64. In this case (TARGET_AARCH64), ARM_MAX_VQ was already 
defined as 16, so there should not be any change.

Other values depending on ARM_MAX_VQ, for migration, are as well under 
TARGET_AARCH64 ifdefs (vmstate_zreg_hi_reg, vmstate_preg_reg, vmstate_vreg).

And for vmstate_vfp, which is present for aarch32 as well, the size of 
data under each register is specifically set to 2.
VMSTATE_UINT64_SUB_ARRAY(env.vfp.zregs[0].d, ARMCPU, 0, 2)

So even if storage has more space, it should not impact any usage of it.

Even though this change is trivial, I didn't do it blindly to "make it 
compile" and I checked the various usages of ARM_MAX_VQ and zregs, and I 
didn't see anything that seems to be a problem.

>>
>> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>> ---
>>    target/arm/cpu.h | 6 +-----
>>    1 file changed, 1 insertion(+), 5 deletions(-)
>>
>> diff --git a/target/arm/cpu.h b/target/arm/cpu.h
>> index 27a0d4550f2..00f78d64bd8 100644
>> --- a/target/arm/cpu.h
>> +++ b/target/arm/cpu.h
>> @@ -169,11 +169,7 @@ typedef struct ARMGenericTimer {
>>     * Align the data for use with TCG host vector operations.
>>     */
>>    
>> -#ifdef TARGET_AARCH64
>> -# define ARM_MAX_VQ    16
>> -#else
>> -# define ARM_MAX_VQ    1
>> -#endif
>> +#define ARM_MAX_VQ    16
>>    
>>    typedef struct ARMVectorReg {
>>        uint64_t d[2 * ARM_MAX_VQ] QEMU_ALIGNED(16);
>