[Crash-utility] [BUG?] failed to execute bt -a for arm64

[Zhi-zhou Zhang]

Hi All,

I try to use `bt -a' for arm64 platform, then Segmentation fault
happened. My crash is built from source code hosted on github. And my
kernel version is 4.4.35.

I tried to use gdb to examine this problem, Some information is shown
as below:

(gdb) bt 
#0  arm64_is_kernel_exception_frame (bt=bt at entry=0x7ffeba6577e0, stkptr=stkptr at entry=18446743803091823872) at arm64.c:1504
#1  0x00000000004fbda8 in arm64_back_trace_cmd (bt=0x7ffeba6577e0) at arm64.c:2259
#2  0x00000000004d415c in back_trace (bt=bt at entry=0x7ffeba6577e0) at kernel.c:3063
#3  0x00000000004dee87 in cmd_bt () at kernel.c:2701
[...]
(gdb) p/x stkptr
$14 = 0xffffffc0fded2d00
(gdb) p/x bt->stackbase
$15 = 0xffffff8008dcc000

As it is, (stkptr - bt->stackbase) is too large. It lead
bt->stackbuf[(ulong)(STACK_OFFSET_TYPE(stkptr))] index out of bounds.
This stack belongs to swapper/0. I'm not sure whether it is a BUG.
Could anyone give me some advise to solve this problem? Thank you!