[Crash-utility] arm64: odd backtrace?

[AKASHI Takahiro]

Dave,

When I ran "bt" against a process running in a user mode, I got
an odd backtrace result:
===8<===
crash> ps
   ...
>  1324   1223   2  ffff80002018be80  RU   0.0     960    468  dhry
   1325      2   1  ffff800021089900  IN   0.0       0      0  [kworker/u16:0]
crash> bt 1324
PID: 1324   TASK: ffff80002018be80  CPU: 2   COMMAND: "dhry"
ffff800022f6ae08: ffff00000812ae44 (crash_save_cpu on IRQ stack)
 #0 [ffff800022f6ae10] crash_save_cpu at ffff00000812ae44
 #1 [ffff800022f6ae60] handle_IPI at ffff00000808e718
 #2 [ffff800022f6b020] gic_handle_irq at ffff0000080815f8
 #3 [ffff800022f6b050] el0_irq_naked at ffff000008084c4c
pt_regs: ffff800022f6af60
     PC: ffffffffffffffff  [unknown or invalid address]
     LR: ffff800020107ed0  [unknown or invalid address]
     SP: 0000000000000000  PSTATE: 004016a4
    X29: ffff000008084c4c  X28: ffff800022f6b080  X27: ffff000008e60c54
    X26: ffff800020107ed0  X25: 0000000000001fff  X24: 0000000000000003
    X23: ffff0000080815f8  X22: ffff800022f6b040  X21: 0000000000000000
    X20: ffff000008bce000  X19: ffff00000808e758  X18: ffff800022f6b010
    X17: ffff00000808a820  X16: ffff800022f6aff0  X15: 0000000000000000
    X14: 0000000000000000  X13: 0000000000000000  X12: 0000000000402138
    X11: ffff000008675850  X10: ffff800022f6afe0   X9: 0000000000000000
     X8: ffff800022f6afc0   X7: 0000000000000000   X6: 0000000000000000
     X5: 0000000000000000   X4: 0000000000000001   X3: 0000000000000000
     X2: 0000000000493000   X1: 0000000000498000   X0: ffffffffffffffff
    ORIG_X0: 0000000020000000  SYSCALLNO: 4021f0
bt: WARNING: arm64_unwind_frame: on IRQ stack: oriq_sp: ffff800020107ed0 fp: 0 (?)
pt_regs: ffff800020107ed0
     PC: 00000000004016a4   LR: 00000000004016a4   SP: 0000ffffc10c40a0
    X29: 0000ffffc10c40a0  X28: 0000000000000000  X27: 0000000000000000
    X26: 0000000000000000  X25: 0000000000402138  X24: 00000000004021f0
    X23: 0000000000000000  X22: 0000000000000000  X21: 00000000004001a0
    X20: 0000000000000000  X19: 0000000000000000  X18: 0000000000000000
    X17: 0000000000000001  X16: 0000000000000000  X15: 0000000000493000
    X14: 0000000000498000  X13: ffffffffffffffff  X12: 0000000000000005
    X11: 000000000000001e  X10: 0101010101010101   X9: fffffffff59a9190
     X8: 7f7f7f7f7f7f7f7f   X7: 1f535226301f2b4c   X6: 00000003001d1000
     X5: 00101d0003000000   X4: 0000000000000000   X3: 4952545320454d4f
     X2: 0000000010c35b40   X1: 0000000000000011   X0: 0000000010c35b40
    ORIG_X0: 0000000000498700  SYSCALLNO: ffffffffffffffff  PSTATE: 20000000
===>8===

* PC, LR and SP look wrong.
  I don't know how those pt_regs values were derived.
* The message, "WARNING: arm64_unwind_frame: on IRQ stack: oriq_sp:
  ffff800020107ed0 fp: 0 (?)" should be refined.
  Apparently, in this case, the process is running in a user mode,
  and so there is no normal kernel stack.

Thanks,
-Takahiro AKASHI