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

[Dave Anderson]

----- Original Message -----
> 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 note your reference to github, but what version of crash are you using?
The only thing that comes to mind is this fix that went into crash-7.1.8:

  - Fix for the ARM64 "bt" command in Linux 4.10 and later kernels that
    are configured with CONFIG_THREAD_INFO_IN_TASK.  Without the patch,
    the "bt" command will fail for active tasks in dumpfiles that were
    generated by the kdump facility.
    (takahiro.akashi at linaro.org)

But since you are using kernel version 4.4.35, that is presumably not
the problem.  
 
> 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!

The closest sample arm64 kernel I have available is 4.5-based, and looking
at the kernel virtual address space, both the stkptr and stackbase values 
above are out of range, so I'm not sure what's going on: 

crash> mach
       MACHINE TYPE: aarch64
        MEMORY SIZE: 16 GB
               CPUS: 1
                 HZ: 1000
          PAGE SIZE: 65536
KERNEL VIRTUAL BASE: ffff800000000000
KERNEL VMALLOC BASE: ffff000000000000
KERNEL MODULES BASE: ffff7ffffc000000
KERNEL VMEMMAP BASE: ffff7fbfe0000000
  KERNEL STACK SIZE: 16384
     IRQ STACK SIZE: 16384
         IRQ STACKS:
              CPU 0: ffff8003ffe30020
              CPU 1: ffff8003ffe60020
              CPU 2: ffff8003ffe90020
              CPU 3: ffff8003ffec0020
              CPU 4: ffff8003ffef0020
              CPU 5: ffff8003fff20020
              CPU 6: ffff8003fff50020
              CPU 7: ffff8003fff80020
crash>

Dave
 





 
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