Re: [PATCH 5/7] hw/hyperv/syndbg: common compilation unit

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

On 3/7/25 03:07, Maciej S. Szmigiero wrote:
> On 6.03.2025 23:56, Pierrick Bouvier wrote:
>> On 3/6/25 09:58, Philippe Mathieu-Daudé wrote:
>>> On 6/3/25 17:23, Pierrick Bouvier wrote:
>>>> On 3/6/25 08:19, Richard Henderson wrote:
>>>>> On 3/5/25 22:41, Pierrick Bouvier wrote:
>>>>>> Replace TARGET_PAGE.* by runtime calls
>>>>>>
>>>>>> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>>>>>> ---
>>>>>>      hw/hyperv/syndbg.c    | 7 ++++---
>>>>>>      hw/hyperv/meson.build | 2 +-
>>>>>>      2 files changed, 5 insertions(+), 4 deletions(-)
>>>>>>
>>>>>> diff --git a/hw/hyperv/syndbg.c b/hw/hyperv/syndbg.c
>>>>>> index d3e39170772..f9382202ed3 100644
>>>>>> --- a/hw/hyperv/syndbg.c
>>>>>> +++ b/hw/hyperv/syndbg.c
>>>>>> @@ -14,7 +14,7 @@
>>>>>>      #include "migration/vmstate.h"
>>>>>>      #include "hw/qdev-properties.h"
>>>>>>      #include "hw/loader.h"
>>>>>> -#include "cpu.h"
>>>>>> +#include "exec/target_page.h"
>>>>>>      #include "hw/hyperv/hyperv.h"
>>>>>>      #include "hw/hyperv/vmbus-bridge.h"
>>>>>>      #include "hw/hyperv/hyperv-proto.h"
>>>>>> @@ -188,7 +188,8 @@ static uint16_t handle_recv_msg(HvSynDbg *syndbg,
>>>>>> uint64_t outgpa,
>>>>>>                                      uint64_t timeout, uint32_t
>>>>>> *retrieved_count)
>>>>>>      {
>>>>>>          uint16_t ret;
>>>>>> -    uint8_t data_buf[TARGET_PAGE_SIZE - UDP_PKT_HEADER_SIZE];
>>>>>> +    const size_t buf_size = qemu_target_page_size() -
>>>>>> UDP_PKT_HEADER_SIZE;
>>>>>> +    uint8_t *data_buf = g_alloca(buf_size);
>>>>>>          hwaddr out_len;
>>>>>>          void *out_data;
>>>>>>          ssize_t recv_byte_count;
>>>>>
>>>>> We've purged the code base of VLAs, and those are preferable to alloca.
>>>>> Just use g_malloc and g_autofree.
>>>>>
>>>>
>>>> I hesitated, due to potential performance considerations for people
>>>> reviewing the patch. I'll switch to heap based storage.
>>>
>>> OTOH hyperv is x86-only, so we could do:
>>>
>>> #define BUFSZ (4 * KiB)
>>>
>>> handle_recv_msg()
>>> {
>>>      uint8_t data_buf[BUFSZ - UDP_PKT_HEADER_SIZE];
>>>      ...
>>>
>>> hv_syndbg_class_init()
>>> {
>>>      assert(BUFSZ > qemu_target_page_size());
>>>      ...
>>>
>>> and call it a day.
>>
>> Could be possible for now yes.
>>
>> Any opinion from concerned maintainers?
> 
> I think essentially hardcoding 4k pages in hyperv is okay
> (with an appropriate checking/enforcement asserts() of course),
> since even if this gets ported to ARM64 at some point
> it is going to need *a lot* of changes anyway.
> 

Ok, I will hardcode this following Philippe suggestion then.

> Thanks,
> Maciej
>