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

[Yumin Qi]

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;


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

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