RFR: JDK-8257828: SafeFetch may crash if invoked in non-JavaThreads [v2]

[David Holmes]

On 14/12/2020 3:24 pm, Thomas Stuefe wrote:
> On Mon, 14 Dec 2020 04:44:43 GMT, David Holmes <dholmes at openjdk.org> wrote:
> 
>>> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
>>>
>>>    Make SafeFetch work on Windows + AIX fix
>>
>> src/hotspot/os/windows/os_windows.cpp line 2258:
>>
>>> 2256:   // Save pc in thread
>>> 2257:   if (thread != nullptr && thread->is_Java_thread()) {
>>> 2258:     thread->as_Java_thread()->set_saved_exception_pc((address)(DWORD_PTR)exceptionInfo->ContextRecord->PC_NAME);
>>
>> Is this a full fix? If the thread is not a JavaThread we no longer hit a problem in as_Java_thread() but is doing nothing for a non-JavaThread actually the right thing to do?
> 
> The saved_exception_pc mechanism is only implemented for JavaThreads. But all threads go through the code below, where we change the pc in the context structure.

My query is whether it makes sense for only JavaThreads to have this 
saved (C++?) exception pc? What role does it play and why would it not 
be applicable to all threads? (Sorry bit of a digression but trying to 
understand the bigger picture.)

Thanks,
David

> -------------
> 
> PR: https://git.openjdk.java.net/jdk/pull/1695
>