CORE ANALYSIS SUITE

  The core analysis suite is a self-contained tool that can be used to

  investigate either live systems, kernel core dumps created from dump

  creation facilities such as kdump, kvmdump, xendump, the netdump and

  diskdump packages offered by Red Hat, the LKCD kernel patch, the mcore

  kernel patch created by Mission Critical Linux, as well as other formats

  created by manufacturer-specific firmware.

  o  The tool is loosely based on the SVR4 crash command, but has been

     completely integrated with gdb in order to be able to display 

     formatted kernel data structures, disassemble source code, etc.

  o  The current set of available commands consist of common kernel core

     analysis tools such as a context-specific stack traces, source code

     disassembly, kernel variable displays, memory display, dumps of 

     linked-lists, etc.  In addition, any gdb command may be entered,

     which in turn will be passed onto the gdb module for execution.  

  o  There are several commands that delve deeper into specific kernel

     subsystems, which also serve as templates for kernel developers

     to create new commands for analysis of a specific area of interest.

     Adding a new command is a simple affair, and a quick recompile

     adds it to the command menu.

  o  The intent is to make the tool independent of Linux version dependencies,

     building in recognition of major kernel code changes so as to adapt to 

     new kernel versions, while maintaining backwards compatibility.

  A whitepaper with complete documentation concerning the use of this utility

  can be found here:

         https://crash-utility.github.io/crash_whitepaper.html

  These are the current prerequisites: 

  o  At this point, x86, ia64, x86_64, ppc64, ppc, arm, arm64, alpha, mips,

     s390 and s390x-based kernels are supported.  Other architectures may be

     addressed in the future.

  o  One size fits all -- the utility can be run on any Linux kernel version

     version dating back to 2.2.5-15.  A primary design goal is to always

     maintain backwards-compatibility.

  o  In order to contain debugging data, the top-level kernel Makefile's CFLAGS

     definition must contain the -g flag.  Typically distributions will contain

     a package containing a vmlinux file with full debuginfo data.  If not, the

     kernel must be rebuilt:

     For 2.2 kernels that are not built with -g, change the following line:

        CFLAGS = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer

     to:

        CFLAGS = -g -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer

     For 2.4 kernels that are not built with -g, change the following line:

        CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -fno-strict-aliasing

     to:

        CFLAGS := -g $(CPPFLAGS) -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -fno-strict-aliasing

     For 2.6 and later kernels that are not built with -g, the kernel should

     be configured with CONFIG_DEBUG_INFO enabled, which in turn will add

     the -g flag to the CFLAGS setting in the kernel Makefile.

     After the kernel is re-compiled, the uncompressed "vmlinux" kernel

     that is created in the top-level kernel build directory must be saved.

  To build the crash utility: 

    $ tar -xf crash-7.2.8.tar.gz

    $ cd crash-7.2.8

    $ make

  The initial build will take several minutes  because the embedded gdb module

  must be configured and built.  Alternatively, the crash source RPM file

  may be installed and built, and the resultant crash binary RPM file installed.

  The crash binary can only be used on systems of the same architecture as

  the host build system.  There are a few optional manners of building the

  crash binary:

  o  On an x86_64 host, a 32-bit x86 binary that can be used to analyze

     32-bit x86 dumpfiles may be built by typing "make target=X86".

  o  On an x86 or x86_64 host, a 32-bit x86 binary that can be used to analyze

     32-bit arm dumpfiles may be built by typing "make target=ARM".

  o  On an x86 or x86_64 host, a 32-bit x86 binary that can be used to analyze

     32-bit mips dumpfiles may be built by typing "make target=MIPS".

  o  On an ppc64 host, a 32-bit ppc binary that can be used to analyze

     32-bit ppc dumpfiles may be built by typing "make target=PPC".

  o  On an x86_64 host, an x86_64 binary that can be used to analyze

     arm64 dumpfiles may be built by typing "make target=ARM64".

  o  On an x86_64 host, an x86_64 binary that can be used to analyze

     ppc64le dumpfiles may be built by typing "make target=PPC64".

  Traditionally when vmcores are compressed via the makedumpfile(8) facility

  the libz compression library is used, and by default the crash utility

  only supports libz.  Recently makedumpfile has been enhanced to optionally

  use either the LZO or snappy compression libraries.  To build crash with

  either or both of those libraries, type "make lzo" or "make snappy".

  All of the alternate build commands above are "sticky" in that the

  special "make" targets only have to be entered one time; all subsequent

  builds will follow suit.

  If the tool is run against a kernel dumpfile, two arguments are required, the

  uncompressed kernel name and the kernel dumpfile name.  

  If run on a live system, only the kernel name is required, because /dev/mem 

  will be used as the "dumpfile".  On Red Hat or Fedora kernels where the

  /dev/mem device is restricted, the /dev/crash memory driver will be used.

  If neither /dev/mem or /dev/crash are available, then /proc/kcore will be

  be used as the live memory source.  If /proc/kcore is also restricted, then

  the Red Hat /dev/crash driver may be compiled and installed; its source

  is included in the crash-7.2.8/memory_driver subdirectory.

  If the kernel file is stored in /boot, /, /boot/efi, or in any /usr/src

  or /usr/lib/debug/lib/modules subdirectory, then no command line arguments

  are required -- the first kernel found that matches /proc/version will be

  used as the namelist.

  For example, invoking crash on a live system would look like this:

    $ crash

    crash 7.2.8

    Copyright (C) 2002-2020  Red Hat, Inc.

    Copyright (C) 2004, 2005, 2006, 2010  IBM Corporation

    Copyright (C) 1999-2006  Hewlett-Packard Co

    Copyright (C) 2005, 2006, 2011, 2012  Fujitsu Limited

    Copyright (C) 2006, 2007  VA Linux Systems Japan K.K.

    Copyright (C) 2005, 2011  NEC Corporation

    Copyright (C) 1999, 2002, 2007  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 7.6

    Copyright 2013 Free Software Foundation, Inc.

    License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

    This is free software: you are free to change and redistribute it.

    There is NO WARRANTY, to the extent permitted by law.  Type "show copying"

    and "show warranty" for details.

    This GDB was configured as "i686-pc-linux-gnu"...

          KERNEL: /boot/vmlinux

        DUMPFILE: /dev/mem

            CPUS: 1

            DATE: Thu Jan 30 13:58:56 2020

          UPTIME: 10 days, 22:55:18

    LOAD AVERAGE: 0.08, 0.03, 0.01

           TASKS: 42

        NODENAME: ha2.mclinux.com

         RELEASE: 2.4.0-test10

         VERSION: #11 SMP Thu Nov 4 15:09:25 EST 2000

         MACHINE: i686  (447 MHz)

	  MEMORY: 128 MB

             PID: 3621                                  

         COMMAND: "crash"

            TASK: c463c000  

             CPU: 0

           STATE: TASK_RUNNING (ACTIVE)

    crash> help

    *              extend         log            rd             task           

    alias          files          mach           repeat         timer          

    ascii          foreach        mod            runq           tree           

    bpf            fuser          mount          search         union          

    bt             gdb            net            set            vm             

    btop           help           p              sig            vtop           

    dev            ipcs           ps             struct         waitq          

    dis            irq            pte            swap           whatis         

    eval           kmem           ptob           sym            wr             

    exit           list           ptov           sys            q              

    crash version: 7.2.8    gdb version: 7.6

    For help on any command above, enter "help <command>".

    For help on input options, enter "help input".

    For help on output options, enter "help output".

    crash> 

  When run on a dumpfile, both the kernel namelist and dumpfile must be 

  entered on the command line.  For example, when run on a core dump created

  by the Red Hat netdump or diskdump facilities:

    $ crash vmlinux vmcore

    crash 7.2.8

    Copyright (C) 2002-2020  Red Hat, Inc.

    Copyright (C) 2004, 2005, 2006, 2010  IBM Corporation

    Copyright (C) 1999-2006  Hewlett-Packard Co

    Copyright (C) 2005, 2006, 2011, 2012  Fujitsu Limited

    Copyright (C) 2006, 2007  VA Linux Systems Japan K.K.

    Copyright (C) 2005, 2011  NEC Corporation

    Copyright (C) 1999, 2002, 2007  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 7.6

    Copyright 2013 Free Software Foundation, Inc.

    License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

    This is free software: you are free to change and redistribute it.

    There is NO WARRANTY, to the extent permitted by law.  Type "show copying"

    and "show warranty" for details.

    This GDB was configured as "i686-pc-linux-gnu"...

          KERNEL: vmlinux

        DUMPFILE: vmcore

            CPUS: 4

            DATE: Tue Mar  2 13:57:09 2004

          UPTIME: 00:02:40

    LOAD AVERAGE: 2.24, 0.96, 0.37

           TASKS: 70

        NODENAME: pro1.lab.boston.redhat.com

         RELEASE: 2.6.3-2.1.214.11smp

         VERSION: #1 SMP Tue Mar 2 10:58:27 EST 2004

         MACHINE: i686  (2785 Mhz)

          MEMORY: 512 MB

           PANIC: "Oops: 0002 [#1]" (check log for details)

             PID: 0

         COMMAND: "swapper"

            TASK: 22fa200  (1 of 4)  [THREAD_INFO: 2356000]

             CPU: 0

           STATE: TASK_RUNNING (PANIC)

    crash> 

  The tool's environment is context-specific.  On a live system, the default

  context is the command itself; on a dump the default context will be the

  task that panicked.  The most commonly-used commands are:

    set     - set a new task context by pid, task address, or cpu.

    bt      - backtrace of the current context, or as specified with arguments.

    p       - print the contents of a kernel variable.

    rd      - read memory, which may be either kernel virtual, user virtual, or

              physical.

    ps      - simple process listing.

    log     - dump the kernel log_buf.

    struct  - print the contents of a structure at a specified address.

    foreach - execute a command on all tasks, or those specified, in the system.

  Detailed help concerning the use of each of the commands in the menu above 

  may be displayed by entering "help command", where "command" is one of those 

  listed above.  Rather than getting bogged down in details here, simply

  run the help command on each of the commands above.  Note that many commands

  have multiple options so as to avoid the proliferation of command names.

  Command output may be piped to external commands or redirected to files.

  Enter "help output" for details.

  The command line history mechanism allows for command-line recall and 

  command-line editing.  Input files containing a set of crash commands may 

  be substituted for command-line input.  Enter "help input" for details.

  Note that a .crashrc file (or .<your-command-name>rc if the name has been 

  changed), may contain any number of "set" or "alias" commands -- see the

  help pages on those two commands for details.

  Lastly, if a command is entered that is not recognized, it is checked

  against the kernel's list of variables, structure, union or typedef names, 

  and if found, the command is passed to "p", "struct", "union" or "whatis".

  That being the case, as long as a kernel variable/structure/union name is 

  different than any of the current commands.

  (1) A kernel variable can be dumped by simply entering its name:

      crash> init_mm

      init_mm = $2 = {

        mmap = 0xc022d540, 

        mmap_avl = 0x0, 

        mmap_cache = 0x0, 

        pgd = 0xc0101000, 

        count = {

          counter = 0x6

        }, 

        map_count = 0x1, 

        mmap_sem = {

          count = {

            counter = 0x1

          }, 

          waking = 0x0, 

          wait = 0x0

        }, 

        context = 0x0, 

        start_code = 0xc0000000, 

        end_code = 0xc022b4c8,

        end_data = c0250388,

        ...

  (2) A structure or can be dumped simply by entering its name and address:  

      crash> vm_area_struct c5ba3910

      struct vm_area_struct {

        vm_mm = 0xc3ae3210, 

        vm_start = 0x821b000, 

        vm_end = 0x8692000, 

        vm_next = 0xc5ba3890, 

        vm_page_prot = {

          pgprot = 0x25

        }, 

        vm_flags = 0x77, 

        vm_avl_height = 0x4, 

        vm_avl_left = 0xc0499540, 

        vm_avl_right = 0xc0499f40, 

        vm_next_share = 0xc04993c0, 

        vm_pprev_share = 0xc0499060, 

        vm_ops = 0x0, 

        vm_offset = 0x0, 

        vm_file = 0x0, 

        vm_pte = 0x0

      }

  The crash utility has been designed to facilitate the task of adding new 

  commands.  New commands may be permanently compiled into the crash executable,

  or dynamically added during runtime using shared object files.

  To permanently add a new command to the crash executable's menu:

    1. For a command named "xxx", put a reference to cmd_xxx() in defs.h.

    2. Add cmd_xxx into the base_command_table[] array in global_data.c. 

    3. Write cmd_xxx(), putting it in one of the appropriate files.  Look at 

       the other commands for guidance on getting symbolic data, reading

       memory, displaying data, etc...

    4. Recompile and run.

  Note that while the initial compile of crash, which configures and compiles

  the gdb module, takes several minutes, subsequent re-compiles to do such

  things as add new commands or fix bugs just takes a few seconds.

  Alternatively, you can create shared object library files consisting of

  crash command extensions, that can be dynamically linked into the crash

  executable during runtime or during initialization.  This will allow

  the same shared object to be used with subsequent crash releases without

  having to re-merge the command's code into each new set of crash sources.

  The dynamically linked-in commands will automatically show up in the crash

  help menu.  For details, enter "help extend" during runtime, or enter

  "crash -h extend" from the shell command line.