[10]RFR: 6415680: (bf) MappedByteBuffer.get() can provoke crash with EXCEPTION_IN_PAGE_ERROR

[dean.long at oracle.com]

Adding runtime alias...

comments inlined below.


On 11/13/17 9:10 PM, jamsheed wrote:

> Hi, request for review, jbs: 
> https://bugs.openjdk.java.net/browse/JDK-6415680 webrev: 
> http://cr.openjdk.java.net/~jcm/6415680/webrev.00/ Description: 1) 
> changes equivalent to JDK-4454115 is done for windows.

It looks like "nm" can be uninitialized if "in_java" is false.

> 2) added guard to multiple value access sites, Unsafe_CopyMemory0, 
> Unsafe_SetMemory0 and Unsafe_CopySwapMemory0.

Can you narrow the scope of the unsafe access using something like 
GuardUnsafeAccess, instead of marking the whole function as doing unsafe 
access?

There are some risks with trying to  abort a copy function.

First, won't we get multiple exceptions until we finally hit the end of 
the range?  What if the bad range is very large?

Second, what if the loop is using auto-increment instructions? Skipping 
to the next instruction would mean we loop forever if the increment 
never happens.

I think if we are going to safely abort copy functions then we need to 
register them as a kind of CodeBlob that has a special abort entry point 
or exception handler we can redirect to, or maybe pop the whole frame 
and return.

Is there really a problem with these copy functions?  I'm wondering why 
Mikael did not identify these as a problem in 8154592.

> 3) Unsafe_CopySwapMemory0 is JVM_LEAF so removed 
> thread->thread_state() == _thread_in_vm checks from signal handler

How about adding a check for _thread_in_native instead of removing the 
check entirely?

dl

> Best regards, Jamsheed
>