Stack unwinder for SA

[Chris Plummer]

On 1/24/21 7:14 PM, David Holmes wrote:
> On 25/01/2021 12:41 pm, Yasumasa Suenaga wrote:
>> Hi all,
>>
>> Chris and I discussed about fixing JDK-8245234 to see all mixed 
>> stacks via `jhsdb jstack --mixed`.
>> In the discussion, we agree to use stack unwinder, but we haven't yet 
>> decided which library to use.
>> Can you suggest the stack unwinder for SA?
>>
>> I fixed similar issue in JDK-8234624 to understand DWARF in SA for 
>> Linux, however it does not support DWARF completely because it is too 
>> complex to implement by scratch.
>> AMD64 SysV ABI [1] says DWARF is used for stack unwinding. So we need 
>> to support DWARF completely if we want to unwind.
>>
>> There are some stack unwinder. I think libunwind [2] is suitable for 
>> this purpose, however I'm not sure it is the best solution.
>> And also I saw similar issue on Windows because we cannot depend on 
>> base pointer (like SA) in Windows x64 [3]. So I want to use the 
>> library which is support both Linux and Windows.
>>
>> We also think introducing stack unwinder helps improving native call 
>> stacks in hs_err log. It will help troubleshooters.
>
> Immediate reaction to this part is that I would not want third-party 
> libraries getting involved in hs_err file generation. Given we often 
> do this from a signal handling context, it would be far too risky IMO.
>
This is probably much less of an issues for hs_err stack dumps than for 
SA, since the crashed thread is almost always in JDK code, so we can 
still get the stack trace for the hs_err file. The issue with SA and 
JDK-8234624 is when you try to dump all threads (with --mixed). Any that 
are waiting in a clib function only show the frame they are in. In 
debug.cpp there are a couple of thread dumping APIs that probably also 
suffer from the problem described in JDK-8245234, so that's possibly 
where some hotspot improvements could be made.

Chris
> Cheers,
> David
> -----
>
>>
>> I want to hear your opinions!
>>
>>
>> Thanks,
>>
>> Yasumasa
>>
>>
>> [1] 
>> https://software.intel.com/sites/default/files/article/402129/mpx-linux64-abi.pdf 
>>
>> [2] https://github.com/libunwind/libunwind
>> [3] 
>> https://docs.microsoft.com/en-us/cpp/build/exception-handling-x64#unwind-procedure 
>>