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
