Re: [Qemu-devel] [PATCH 08/11] tcg/aarch64: Make direct jump patching thread-safe

[Alex Bennée]

Richard Henderson <address@hidden> writes:

> On 04/20/2016 07:01 AM, Alex Bennée wrote:
>>
>> Sergey Fedorov <address@hidden> writes:
>>
>>> From: Sergey Fedorov <address@hidden>
>>>
>>> Ensure direct jump patching in AArch64 is atomic by using
>>> atomic_read()/atomic_set() for code patching.
>>>
>>> Signed-off-by: Sergey Fedorov <address@hidden>
>>> Signed-off-by: Sergey Fedorov <address@hidden>
>>> ---
>>>   tcg/aarch64/tcg-target.inc.c | 14 +++++++++++++-
>>>   1 file changed, 13 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/tcg/aarch64/tcg-target.inc.c b/tcg/aarch64/tcg-target.inc.c
>>> index 0ed10a974121..15fdebec921f 100644
>>> --- a/tcg/aarch64/tcg-target.inc.c
>>> +++ b/tcg/aarch64/tcg-target.inc.c
>>> @@ -73,6 +73,18 @@ static inline void reloc_pc26(tcg_insn_unit *code_ptr, 
>>> tcg_insn_unit *target)
>>>       *code_ptr = deposit32(*code_ptr, 0, 26, offset);
>>>   }
>>>
>>> +static inline void reloc_pc26_atomic(tcg_insn_unit *code_ptr,
>>> +                                     tcg_insn_unit *target)
>>> +{
>>> +    ptrdiff_t offset = target - code_ptr;
>>> +    tcg_insn_unit insn;
>>> +    assert(offset == sextract64(offset, 0, 26));
>>> +    /* read instruction, mask away previous PC_REL26 parameter contents,
>>> +       set the proper offset, then write back the instruction. */
>>
>> This comment could be moved from here and reloc_pc26 and made common for
>> the two following functions.
>
> There's a significant amount of cleanup that ought to happen here, now that
> we're not re-translating TBs.  I don't know if Sergey should be gated
> on that.

Is this stuff already in the works? Otherwise we are trying to get
pre-cursors to MTTCG into the code (once the tree re-opens) to keep the
main diff down. This also is beneficial for linux-user stuff.

>
>
> r~


--
Alex Bennée