Re: [PATCH v2 05/26] xen/riscv: introduce guest riscv,isa string

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.05.2026 13:59, Oleksii Kurochko wrote:
> On 5/18/26 5:51 PM, Jan Beulich wrote:
>> On 08.05.2026 16:43, Oleksii Kurochko wrote:
>>> --- a/xen/arch/riscv/include/asm/cpufeature.h
>>> +++ b/xen/arch/riscv/include/asm/cpufeature.h
>>> @@ -17,6 +17,8 @@
>>>    */
>>>   #define RISCV_ISA_EXT_BASE  26
>>>   
>>> +#define RISCV_GUEST_ISA_STR_MAX 256
>>
>> This looks like it won't be good for very long, seeing how long ISA strings 
>> can
>> get. I wonder anyway whether ...
>>
>>> @@ -94,6 +95,9 @@ struct arch_domain {
>>>       struct p2m_domain p2m;
>>>   
>>>       struct paging_domain paging;
>>> +
>>> +    DECLARE_BITMAP(guest_isa, RISCV_ISA_EXT_MAX);
>>> +    char guest_isa_str[RISCV_GUEST_ISA_STR_MAX];
>>
>> ... a compile-time sized buffer is suitable here. Can't you allocate a buffer
>> just large enough to hold the string?
> 
> It could be allocated dynamically.
> 
> Does it make sense to evaluate in run-time what should be a buffer size? 
> For this case I can't find analogue of realloc() in Xen.

Hmm, I see xrealloc_array(), and surely we could gain xvrealloc_array()
which we'll need anyway once xrealloc_array() uses get converted. (I also
see x{,v}realloc_flex_struct(), but that's of no use here as it looks.)

> Or it would be 
> fine just to take something bigger as a const (lets say 2048) and use it 
> for dynamic allocation?

I'd rather not. Can't you determine how much space the string is going to
occupy?

Jan