RFR 8191278: MappedByteBuffer bulk access memory failures are not handled gracefully

[Vladimir Kozlov]

Hi Jamsheed,

Instead of finding PC in stubs we should use something similar to GuardUnsafeAccess to set thread's 
doing_unsafe_access flag when we call copy stub for unsafe memory as you suggested first (in bug 
report).

Interpreter set the flag for Unsafe.CopyMemory0() and Unsafe.copySwapMemory0(). C2 has intrinsic 
only for CopyMemory0():

http://hg.openjdk.java.net/jdk/jdk/file/6ad0281a654e/src/hotspot/share/opto/library_call.cpp#l4189

It only use unsafe_arraycopy stab:

http://hg.openjdk.java.net/jdk/jdk/file/6ad0281a654e/src/hotspot/cpu/x86/stubGenerator_x86_64.cpp#l2434

Setting on it's entry and cleaning on exit Thread::_doing_unsafe_access field should be enough. Right?

Or I am missing something?

An other thing which bothering me is Harold's comment:

"Unfortunately, "CompiledMethod* nm" gets set to NULL and so handle_unsafe_access() is not executed."

Where/why nm is NULLed?

Actually I think the whole code for "// BugId 4454115" is questionable since it replaces any crash 
(most likely not related to unsafe access) in compiled method which has at least one unsafe access 
with exception. May be we should use PcDesc to record unsafe instructions and compare with SEGV PC. 
But it is separate RFE. For this one we need to fix only Unsafe.CopyMemory0() C2 inrinsic.

Thanks,
Vladimir

On 4/8/19 4:21 AM, Tobias Hartmann wrote:
> Hi Jamsheed,
> 
> On 05.04.19 15:11, Jamsheed wrote:
>> On 04/04/19 7:23 PM, Andrew Haley wrote:
>>>> this looks reasonable to me although the code is getting quite complicated to handle this edge case.
>>> Yeah, it really is. Can't we just assume that *any* fault in these stubs is
>>> caused via Unsafe, and get rid of bool unsafe_copy_code_range?
>>
>> Thanks for the feedback Tobias, Andrew, removed  unsafe_copy_code_range.
>>
>> webrev: http://cr.openjdk.java.net/~jcm/8191278/webrev.04/
> 
> I think what Andrew meant is basically to go with webrev.01:
> http://cr.openjdk.java.net/~jcm/8191278/webrev.01/
> 
> Right?
> 
> Thanks,
> Tobias
>