From: https://mail.openjdk.java.net/pipermail/jdk-updates-dev/2020-September/003886.html

"""
we have seen several crashes on several platforms after this change was pushed.

Aarch64 example:
Stack: [0x0000ffff90437000,0x0000ffff90637000], sp=0x0000ffff90635520, free space=2041k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x9fb0f8] ObjectSampleCheckpoint::write_stacktrace(JfrStackTrace const*, JfrCheckpointWriter&)+0x208
V [libjvm.so+0x9fb770] StackTraceBlobInstaller::install(ObjectSample*)+0x1b8
V [libjvm.so+0x9fba40] ObjectSampleCheckpoint::on_rotation(ObjectSampler const*, JfrStackTraceRepository&)+0x150
V [libjvm.so+0x72df6c] JfrRecorderService::pre_safepoint_write()+0x3a4
V [libjvm.so+0x72e828] JfrRecorderService::write()+0x58
V [libjvm.so+0x72fd2c] JfrRecorderService::rotate(int)+0x3b4
V [libjvm.so+0x730628] recorderthread_entry(JavaThread*, Thread*)+0x160
V [libjvm.so+0xbb2dd0] JavaThread::thread_main_inner()+0xd8
V [libjvm.so+0xbb08fc] Thread::call_run()+0x94
V [libjvm.so+0xa21718] thread_native_entry(Thread*)+0x108
C [libpthread.so.0+0x7088] start_thread+0xb0

siginfo: si_signo: 11 (SIGSEGV), si_code: 1 (SEGV_MAPERR), si_addr: 0x0000000000000008

This backport uses a different JfrStackFrame constructor (which was probably unused before):
JfrStackFrame::JfrStackFrame(const traceid& id, int bci, int type, int lineno) :
  _method(NULL), _methodid(id), _line(lineno), _bci(bci), _type(type) {}

It sets _method to NULL!

Should probably be:
JfrStackFrame::JfrStackFrame(const traceid& id, int bci, int type, int lineno, const Method* method) :
  _method(method), _methodid(id), _line(lineno), _bci(bci), _type(type) {}

and:
_frames[count] = JfrStackFrame(mid, bci, type, lineno, method);
"""