[Crash-utility] kernel module parsing failure - mips

[Rabin Vincent]

On Sat, Dec 03, 2016 at 01:15:23PM -0800, Sagar Borikar wrote:
> > So the first error should be fixed properly before attempting "mod".  What
> > kernel version is this and what page size do to use?
> 
> 4.4.20 kernel and page size is 16K

I'd only tested 4K pages before but I've now provisioned a QEMU Malta machine
with 16K pages.  I've now sent a patch to the list which fixes the
definition  of __PGD_ORDER.  With only that patch, the pgd size errors
are gone and "mod" works for my 16K kernel/dump:

 crash> sym -n swapper_pg_dir
 80540000 (B) swapper_pg_dir
 80544000 (B) invalid_pte_table
 crash> sys
       KERNEL: vmlinux-16k-unload
    DUMPFILES: /var/tmp/ramdump_elf_wZxP65 [temporary ELF header]
               rawdump-16k-unload
         CPUS: 1
         DATE: Sun Dec  4 14:46:08 2016
       UPTIME: 00:00:21
 LOAD AVERAGE: 0.31, 0.07, 0.02
        TASKS: 54
     NODENAME: buildroot
      RELEASE: 4.4.27-dirty
      VERSION: #12 SMP Sun Dec 4 14:45:32 CET 2016
      MACHINE: mips  (unknown Mhz)
       MEMORY: 128 MB
        PANIC: "Kernel panic - not syncing: Fatal exception"
 crash> help -m | grep -A7 pagesize
            pagesize: 16384
           pageshift: 14
            pagemask: ffffffffffffc000
          pageoffset: 3fff
         pgdir_shift: 26
        ptrs_per_pgd: 64
        ptrs_per_pte: 4096
           stacksize: 16384
 crash> mod
  MODULE   NAME      SIZE  OBJECT FILE
 c01050c0  null_blk  5333  (not loaded)  [CONFIG_KALLSYMS]

With the fixed __PGD_ORDER, PGD_ORDER gets the value zero and that is
correct for my kernel.  __PGD_ORDER isn't used anywhere else that in
PGD_ORDER, so even your hack of forcing PGD_ORDER to zero would have
fixed "mod" for me.

So there could be some other additional problem in your case besides the
incorrect __PGD_ORDER.  Could you please apply the fix and run crash
with the -d8 argument and post the full log?  Thanks.