RFR: JDK-8226878: zero crashes after JDK-8191278

[Jamsheed]

Hi Ao Qi,

On 27/06/19 5:08 PM, Aleksey Shipilev wrote:
> On 6/27/19 1:04 PM, Ao Qi wrote:
>> Hi,
>>
>> On zero, StubRoutines::unsafe_arraycopy() may return
>> ShouldNotCallThisStub() but not NULL. Is it ok to use
>> Copy::conjoint_memory_atomic instead of
>> StubRoutines::UnsafeArrayCopy_stub()(src, dst, sz) on zero?
Yes.
>>
>> JBS:
>> https://bugs.openjdk.java.net/browse/JDK-8226878
>>
>> Fix:
>> diff --git a/src/hotspot/share/prims/unsafe.cpp
>> b/src/hotspot/share/prims/unsafe.cpp
>> --- a/src/hotspot/share/prims/unsafe.cpp
>> +++ b/src/hotspot/share/prims/unsafe.cpp
>> @@ -401,7 +401,7 @@
>>     void* dst = index_oop_from_field_offset_long(dstp, dstOffset);
>>     {
>>       GuardUnsafeAccess guard(thread);
>> -    if (StubRoutines::unsafe_arraycopy() != NULL) {
>> +    if (StubRoutines::unsafe_arraycopy() != NULL ZERO_ONLY(&&
>> StubRoutines::unsafe_arraycopy() != ShouldNotCallThisStub())) {
>>         StubRoutines::UnsafeArrayCopy_stub()(src, dst, sz);
>>       } else {
>>         Copy::conjoint_memory_atomic(src, dst, sz);
> Hold on. I think stubGenerator_zero.cpp should just return NULL when stub is not generated. It looks
> like a Zero-specific problem to return "fake" stubs when they are not actually generated. Like this:
>
> diff -r 91b38bfb9079 src/hotspot/cpu/zero/stubGenerator_zero.cpp
> --- a/src/hotspot/cpu/zero/stubGenerator_zero.cpp       Thu Jun 27 18:00:54 2019 +0800
> +++ b/src/hotspot/cpu/zero/stubGenerator_zero.cpp       Thu Jun 27 13:37:47 2019 +0200
> @@ -157,7 +157,9 @@
>
>       StubRoutines::_checkcast_arraycopy       = ShouldNotCallThisStub();
> -    StubRoutines::_unsafe_arraycopy          = ShouldNotCallThisStub();
>       StubRoutines::_generic_arraycopy         = ShouldNotCallThisStub();
>
> +    // Shared code tests for "NULL" to discover the stub is not generated.
> +    StubRoutines::_unsafe_arraycopy          = NULL;
> +
>       // We don't generate specialized code for HeapWord-aligned source
>       // arrays, so just use the code we've already generated
>
i too think making changes here is more clean.

Thanks and Best regards,

Jamsheed