LLDB fails to unwind stack from minidump

Subprojects LLDB
#1

Here are the commands I used.

(lldb) log enable lldb unwind
(lldb) target create -c minidump.dmp
lldb             AssertFrameRecognizer::GetAbortLocation Unsupported OS
lldb             Process::SetPrivateState (stopped)
lldb             Process::SetPrivateState (stopped) stop_id = 1
intern-state     th25/fr0 with pc value of 0x7ffcedaf478c, no symbol/function name is known.
intern-state     th25/fr0 0x00007ffcedaf478c: CFA=rbp+16 => rbp=[CFA-16] rsp=CFA+0 rip=[CFA-8]
intern-state     th25/fr0 Got an invalid CFA register value - reg rbp (6), value 0x0
intern-state     th25/fr0 could not read CFA value for first frame.
intern-state     th25 Unwind of this thread is complete.
...
(lldb) bt
lldb             th25/fr0 with pc value of 0x7ffcedaf478c, no symbol/function name is known.
lldb             th25/fr0 0x00007ffcedaf478c: CFA=rbp+16 => rbp=[CFA-16] rsp=CFA+0 rip=[CFA-8]
lldb             th25/fr0 Got an invalid CFA register value - reg rbp (6), value 0x0
lldb             th25/fr0 could not read CFA value for first frame.
lldb             th25 Unwind of this thread is complete.
* thread #25, stop reason = Exception 0xe0000008 encountered at address 0x7ffcedaf478c
  * frame #0: 0x00007ffcedaf478c KERNELBASE.dll

It seems like after finding out that rbp has value 0, it stops unwinding. While using minidump_stackwalk, it’s able to unwind stacks by stack scanning (Introduction). Is it something not implemented in lldb?

#2

I haven’t worked with minidumps, but the unwinder has an unwind rule for walking the stack,

lldb             th25/fr0 0x00007ffcedaf478c: CFA=rbp+16 => rbp=[CFA-16] rsp=CFA+0 rip=[CFA-8]

and all of the rules for finding the caller’s stack frame are in terms of rbp (the canonical frame address is defined to be $rbp plus an offset, and the saved rbp/rsp/rip are based on the CFA plus an offset). If lldb doesn’t have a value for RBP, the generic unwinder can’t walk the stack.
(nb: this is using the “architectural default unwind plan” for x86_64, which assumes that there is a frame chain on the stack that it can walk - with spilled rbp and rip values as it goes up)

#3

If lldb doesn’t have a value for RBP, the generic unwinder can’t walk the stack.

Is there a non-generic unwinder that could walk the stack without value for rbp?
If no and we want to add support for walking stack without rbp, where would be the place for adding this?