RFR: 8016538: volatile double access via Unsafe.cpp is not atomic

[Yumin Qi]

I decided to make all the x86 platform with consistent changes so it 
should not be an issue.

Thanks
Yumin

On 7/10/2013 9:20 AM, Christian Thalinger wrote:
> On Jul 10, 2013, at 3:46 AM, David Holmes <david.holmes at oracle.com> wrote:
>
>> On 10/07/2013 2:03 PM, Yumin Qi wrote:
>>> This is from comments I put on jbs:
>>> The same test did not fail on solaris-i586, from disassembled code:
>>> 0xfe9605ff: Unsafe_GetDoubleVolatile+0x00c7: addl 0x00000014(%ebp),%eax
>>> 0xfe960602: Unsafe_GetDoubleVolatile+0x00ca: fldl (%eax)
>>> 0xfe960604: Unsafe_GetDoubleVolatile+0x00cc: fstpl 0xffffffe0(%ebp)
>>> 0xfe960607: Unsafe_GetDoubleVolatile+0x00cf: fldl 0xffffffe0(%ebp)
>>> 0xfe96060a: Unsafe_GetDoubleVolatile+0x00d2: fstpl 0xffffffd0(%ebp)
>>> 0xfe96060d: Unsafe_GetDoubleVolatile+0x00d5: movl 0x00000004(%edi),%eax
>>> 0xfe960610: Unsafe_GetDoubleVolatile+0x00d8: movl %eax,0xffffffd8(%ebp)
>>> 0xfe960613: Unsafe_GetDoubleVolatile+0x00db: movl 0x00000008(%edi),%ecx
>>> 0xfe960616: Unsafe_GetDoubleVolatile+0x00de: cmpl $0x00000000,(%ecx)
>>> 0xfe960619: Unsafe_GetDoubleVolatile+0x00e1: je
>>> Unsafe_GetDoubleVolatile+0x100 [ 0xfe960638, .+0x1f ]
>>>
>>> It is using fldl/fstpl for return *p;
>> Interesting. Thanks,
> But this is more a compile issue than a Linux issue, right?  What if someone builds on Solaris or Mac OS X with plain GCC?
>
> -- Chris
>
>> David
>>
>>> Thanks
>>> Yumin
>>>
>>> On 7/9/2013 5:40 PM, David Holmes wrote:
>>>> Hi Yumin,
>>>>
>>>> On 10/07/2013 4:32 AM, Yumin Qi wrote:
>>>>> Hi,
>>>>>
>>>>>    Can i have your codereview of this change:
>>>>>    Unsafe_Get[SET]DoubleVolatile are not atomic on 32bit x86 linux
>>>>> caused test for
>>>>> org.openjdk.concurrent.torture.tests.atomicity.primitives.reflect.DoubleAtomicityTest
>>>>>
>>>>> failed.
>>>>>    The fix is using same treatment for jdouble as for jlong. Tests
>>>>> passed on failed test case, vm quick tests. It only happens on linux
>>>>> 32bit platform, on solaris, the inlined code be compiled into code of
>>>>> using fldl/fstpl which are atomic instructions.
>>>> Why is this not also a problem on Solaris? What does the Solaris
>>>> compiler generate for
>>>>
>>>> inline jdouble  OrderAccess::load_acquire(volatile jdouble* p) {
>>>> return *p; }
>>>>
>>>>>    Contributed by: dholmes
>>>> Guess that means I can't Review it :)
>>>>
>>>> David
>>>> -----
>>>>
>>>>>    URL: http://cr.openjdk.java.net/~minqi/8016538/01
>>>>>
>>>>>    Thanks
>>>>>    Yumin