Hi David, Chris,
I want to fix `jhsdb jstack --mixed` in JDK-8245234 with third-party library at
first.
Fixing hs_err log is an another issue IMHO, but I just want to say we may
divert it for hs_err log.
We need further discussion for it of course.
Thanks,
Yasumasa
On 2021/01/25 12:32, Chris Plummer wrote:
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
