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

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 20/04/16 18:08, Richard Henderson wrote:
> On 04/20/2016 07:01 AM, Alex Bennée wrote:
>>
>> Sergey Fedorov <sergey.fedorov@linaro.org> writes:
>>
>>> From: Sergey Fedorov <serge.fdrv@gmail.com>
>>>
>>> Ensure direct jump patching in AArch64 is atomic by using
>>> atomic_read()/atomic_set() for code patching.
>>>
>>> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
>>> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org>
>>> ---
>>>   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.

Do you mean I'd better avoid using stuff like reloc_pc26()?

Kind regards,
Sergey