[Crash-utility] relocatable FC7/upstream x86 kernels

[Dave Anderson]

Dave Anderson wrote:
 > So, whereas the vmlinux file shows these symbol values:
 >
 >   $ nm -Bn vmlinux
 >   ...
 >   c1000000 T _text
 >   c1000000 T startup_32
 >   c1001000 T startup_32_smp
 >   c1001080 t checkCPUtype
 >   c1001101 t is486
 >   c1001108 t is386
 >   c1001175 t check_x87
 >   c10011a0 T setup_pda
 >   c10011c2 t setup_idt
 >   c10011df t rp_sidt
 >   c1001262 t early_divide_err
 >   c1001268 t early_illegal_opcode
 >   c1001271 t early_protection_fault
 >   c1001278 t early_page_fault
 >   c100127f t early_fault
 >   c10012a7 t hlt_loop
 >   c10012ac t ignore_int
 >   c10012f0 T _stext
 >   c10012f0 t run_init_process
 >   c10012f0 T stext
 >   c1001304 t init_post
 >   ...
 >
 > But when loaded into memory, they are all changed to reflect that
 > the kernel was loaded at at 4MB physical instead of 16MB:
 >
 >   $ cat /proc/kallsyms
 >   c0400000 T _text
 >   c0400000 T startup_32
 >   c0401000 T startup_32_smp
 >   c0401080 t checkCPUtype
 >   c0401101 t is486
 >   c0401108 t is386
 >   c0401175 t check_x87

Interesting -- I never thought /proc/kallsyms would have ever
come in so handy...

crash fails on my FC7 kernel in the "do not match" manner:

   # crash /vmlinux-2.6.21-1.3194.fc7

   crash 4.0-4.3
   Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007  Red Hat, Inc.
   Copyright (C) 2004, 2005, 2006  IBM Corporation
   Copyright (C) 1999-2006  Hewlett-Packard Co
   Copyright (C) 2005, 2006  Fujitsu Limited
   Copyright (C) 2006, 2007  VA Linux Systems Japan K.K.
   Copyright (C) 2005  NEC Corporation
   Copyright (C) 1999, 2002  Silicon Graphics, Inc.
   Copyright (C) 1999, 2000, 2001, 2002  Mission Critical Linux, Inc.
   This program is free software, covered by the GNU General Public License,
   and you are welcome to change it and/or distribute copies of it under
   certain conditions.  Enter "help copying" to see the conditions.
   This program has absolutely no warranty.  Enter "help warranty" for details.

   GNU gdb 6.1
   Copyright 2004 Free Software Foundation, Inc.
   GDB is free software, covered by the GNU General Public License, and you are
   welcome to change it and/or distribute copies of it under certain conditions.
   Type "show copying" to see the conditions.
   There is absolutely no warranty for GDB.  Type "show warranty" for details.
   This GDB was configured as "i686-pc-linux-gnu"...

   crash: /vmlinux-2.6.21-1.3194.fc7 and /dev/crash do not match!

   Usage:
     crash [-h [opt]][-v][-s][-i file][-d num] [-S] [mapfile] [namelist] [dumpfile]

   Enter "crash -h" for details.

   #

But since /proc/kallsyms has a format similar to a System.map
file, if you throw it on the crash command line, crash thinks
that it is a System.map, and things just work:

   # crash /vmlinux-2.6.21-1.3194.fc7 /proc/kallsyms

   crash 4.0-4.3
   Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007  Red Hat, Inc.
   Copyright (C) 2004, 2005, 2006  IBM Corporation
   Copyright (C) 1999-2006  Hewlett-Packard Co
   Copyright (C) 2005, 2006  Fujitsu Limited
   Copyright (C) 2006, 2007  VA Linux Systems Japan K.K.
   Copyright (C) 2005  NEC Corporation
   Copyright (C) 1999, 2002  Silicon Graphics, Inc.
   Copyright (C) 1999, 2000, 2001, 2002  Mission Critical Linux, Inc.
   This program is free software, covered by the GNU General Public License,
   and you are welcome to change it and/or distribute copies of it under
   certain conditions.  Enter "help copying" to see the conditions.
   This program has absolutely no warranty.  Enter "help warranty" for details.

   GNU gdb 6.1
   Copyright 2004 Free Software Foundation, Inc.
   GDB is free software, covered by the GNU General Public License, and you are
   welcome to change it and/or distribute copies of it under certain conditions.
   Type "show copying" to see the conditions.
   There is absolutely no warranty for GDB.  Type "show warranty" for details.
   This GDB was configured as "i686-pc-linux-gnu"...

   please wait... (patching 28475 gdb minimal_symbol values)

     SYSTEM MAP: /proc/kallsyms
   DEBUG KERNEL: /vmlinux-2.6.21-1.3194.fc7 (2.6.21-1.3194.fc7)
       DUMPFILE: /dev/crash
           CPUS: 4
           DATE: Wed Jul 25 13:47:55 2007
         UPTIME: 23:10:09
   LOAD AVERAGE: 0.08, 0.03, 0.01
          TASKS: 111
       NODENAME: ibm-crichton-01.lab.boston.redhat.com
        RELEASE: 2.6.21-1.3194.fc7
        VERSION: #1 SMP Wed May 23 22:35:01 EDT 2007
        MACHINE: i686  (2666 Mhz)
         MEMORY: 1 GB
            PID: 958
        COMMAND: "crash"
           TASK: c1934d30  [THREAD_INFO: ce64b000]
            CPU: 3
          STATE: TASK_RUNNING (ACTIVE)

   crash> q

Of course if you're running with 2.6.22, you'd then probably bump
into  the issue reported by Ken'ichi:

   [Crash-utility] [Patch] linux-2.6.22 on i386
   https://www.redhat.com/archives/crash-utility/2007-July/msg00061.html

So applying Ken'ichi's patch, and then using /proc/kallsyms, should get
you up and running for now...  (presuming you've got CONFIG_KALLSYMS
configured)

Dave