[Crash-utility] Problem in bt for ARM64

[Dave Anderson]

----- Original Message -----
> Hi Dave
> 
> I have experienced some problems in the bt command for ARM64. It seems that
> the test in arm64_print_exception_frame in arm64.c if the task is running in
> 32 or 64-bit mode in userland does not work. It "always" becomes 32-bit
> mode. Example:
> 
> crash> bt 1
> PID: 1      TASK: ffffffe1f90f8000  CPU: 2   COMMAND: "init"
>  #0 [ffffffe1f9103c80] __switch_to at ffffff85b6a862f8
>  #1 [ffffffe1f9103ca0] __schedule at ffffff85b7b0d9b0
>  #2 [ffffffe1f9103d00] schedule at ffffff85b7b0df28
>  #3 [ffffffe1f9103d20] schedule_hrtimeout_range_clock at ffffff85b7b11308
>  #4 [ffffffe1f9103da0] schedule_hrtimeout_range at ffffff85b7b11320
>  #5 [ffffffe1f9103db0] sys_epoll_wait at ffffff85b6c394c8
>  #6 [ffffffe1f9103e70] sys_epoll_pwait at ffffff85b6c396fc
>  #7 [ffffffe1f9103ed0] el0_svc_naked at ffffff85b6a8312c
>      PC: 00000004  LR: 00000000  SP: 00000000  PSTATE: 00000016
>     X12: 00546694 X11: 3431206c616e6769 X10: 00546338  X9: 00000000
>      X8: 00000112  X7: dfdab819254dd1e8  X6: 00000016  X5: 0000000a
>      X4: 00000031  X3: 00000008  X2: 00000000  X1: ffffffff
>      X0: 00000001
> 
> The register values are:
> r0:                 4   r1:        7ff0b27f90
> r2:                 1   r3:          ffffffff
> r4:                 0   r5:                 8
> r6:                31   r7:                 a
> r8:                16   r9:  dfdab819254dd1e8
> r10:              112   r11:                0
> r12:           546338   r13: 3431206c616e6769
> r14:           546694   r15:                0
> r16:                0   r17:         f04245b7
> r18:         51f2a993   r19:           5783c0
> r20:           415254   r21:           527a5c
> r22:           527e04   r23:         ffffffff
> r24:         ffffffff   r25:           576000
> r26:           578000   r27:           578000
> r28:              3e8   fp:        7ff0b27ec0
> lr:            4f4f24   sp:        7ff0b27eb0
> pc:            4fb8d4   psr:         40000000
> 
> I have unfortunately not had the time to look for a solution, so I just want
> to report what I have seen. The kernel running in the example above is
> 4.4.74 and I have seen the same problem for a 4.9.40 kernel.
> 
> Jan

Yeah, even the functions that do show 64-bit user mode exception frames
appear to have invalid contents.  It looks like the pt_regs is not at the
same fixed location on the stack where it has always been, i.e., as it gets
set here unconditionally at the bottom of arm64_back_trace_cmd():

complete_user:
        exception_frame = bt->stacktop - USER_EFRAME_OFFSET;
        arm64_print_exception_frame(bt, exception_frame, USER_MODE, ofp);

Thanks,
  Dave