Re: [Qemu-devel] [PATCH 03/11] tci: Make direct jump patching thread-safe

[Sergey Fedorov]

On 20/04/16 16:14, Alex Bennée wrote:
> Sergey Fedorov <address@hidden> writes:
>
>> On 20/04/16 12:42, Alex Bennée wrote:
>>> Sergey Fedorov <address@hidden> writes:
>>>> diff --git a/tcg/tci/tcg-target.inc.c b/tcg/tci/tcg-target.inc.c
>>>> index 4afe4d7a8d59..7e6180e62898 100644
>>>> --- a/tcg/tci/tcg-target.inc.c
>>>> +++ b/tcg/tci/tcg-target.inc.c
>>>> @@ -556,6 +556,8 @@ static void tcg_out_op(TCGContext *s, TCGOpcode opc, 
>>>> const TCGArg *args,
>>>>          if (s->tb_jmp_offset) {
>>>>              /* Direct jump method. */
>>>>              assert(args[0] < ARRAY_SIZE(s->tb_jmp_offset));
>>>> +            /* Align for atomic patching and thread safety */
>>>> +            s->code_ptr = (uint8_t *)(((uintptr_t)s->code_ptr + 3) &
>>>> ~3);
>>> Seeing this pattern is being used over and over again I wonder if we
>>> should have some utility helper functions for this? Perhaps we should
>>> steal the kernels ALIGN macros?
>> Good point, really. I see such a macro in hw/display/qxl.c and
>> kvm-all.c. It'd be better a common definition. Any idea of where to
>> put it?
> Somewhere inside include/qemu. osdep.h has ROUND_UP/DOWN functions maybe
> there makes the most sense?

Hmm, ROUND_UP() seems to be exactly what we need here. Though I think
compiler could be smart enough to give the same code with
QEMU_ALIGN_UP() as well. But we'd benefit from something like:

/* n-byte align pointer down */
#define QEMU_ALIGN_PTR_DOWN(p, n) \
    ((typeof(p))QEMU_ALIGN_DOWN((uintptr_t)(p), (n)))

/* n-byte align pointer up */
#define QEMU_ALIGN_PTR_UP(p, n) \
    ((typeof(p))QEMU_ALIGN_UP((uintptr_t)(p), (n)))


Kind regards,
Sergey