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docs: admin-guide: add kdump documentation into it

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The Kdump documentation describes procedures with admins use
in order to solve issues on their systems.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
This commit is contained in:
Mauro Carvalho Chehab
2019-06-13 15:21:39 -03:00
parent 9e1cbede26
commit 330d481052
14 changed files with 15 additions and 15 deletions
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Documentation/admin-guide/kdump/gdbmacros.txt
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#
# This file contains a few gdb macros (user defined commands) to extract
# useful information from kernel crashdump (kdump) like stack traces of
# all the processes or a particular process and trapinfo.
#
# These macros can be used by copying this file in .gdbinit (put in home
# directory or current directory) or by invoking gdb command with
# --command=<command-file-name> option
#
# Credits:
# Alexander Nyberg <alexn@telia.com>
# V Srivatsa <vatsa@in.ibm.com>
# Maneesh Soni <maneesh@in.ibm.com>
#
define bttnobp
set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
set $init_t=&init_task
set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
set var $stacksize = sizeof(union thread_union)
while ($next_t != $init_t)
set $next_t=(struct task_struct *)$next_t
printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
printf "===================\n"
set var $stackp = $next_t.thread.sp
set var $stack_top = ($stackp & ~($stacksize - 1)) + $stacksize
while ($stackp < $stack_top)
if (*($stackp) > _stext && *($stackp) < _sinittext)
info symbol *($stackp)
end
set $stackp += 4
end
set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
while ($next_th != $next_t)
set $next_th=(struct task_struct *)$next_th
printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
printf "===================\n"
set var $stackp = $next_t.thread.sp
set var $stack_top = ($stackp & ~($stacksize - 1)) + stacksize
while ($stackp < $stack_top)
if (*($stackp) > _stext && *($stackp) < _sinittext)
info symbol *($stackp)
end
set $stackp += 4
end
set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
end
set $next_t=(char *)($next_t->tasks.next) - $tasks_off
end
end
document bttnobp
dump all thread stack traces on a kernel compiled with !CONFIG_FRAME_POINTER
end
define btthreadstack
set var $pid_task = $arg0
printf "\npid %d; comm %s:\n", $pid_task.pid, $pid_task.comm
printf "task struct: "
print $pid_task
printf "===================\n"
set var $stackp = $pid_task.thread.sp
set var $stacksize = sizeof(union thread_union)
set var $stack_top = ($stackp & ~($stacksize - 1)) + $stacksize
set var $stack_bot = ($stackp & ~($stacksize - 1))
set $stackp = *((unsigned long *) $stackp)
while (($stackp < $stack_top) && ($stackp > $stack_bot))
set var $addr = *(((unsigned long *) $stackp) + 1)
info symbol $addr
set $stackp = *((unsigned long *) $stackp)
end
end
document btthreadstack
dump a thread stack using the given task structure pointer
end
define btt
set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
set $init_t=&init_task
set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
while ($next_t != $init_t)
set $next_t=(struct task_struct *)$next_t
btthreadstack $next_t
set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
while ($next_th != $next_t)
set $next_th=(struct task_struct *)$next_th
btthreadstack $next_th
set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
end
set $next_t=(char *)($next_t->tasks.next) - $tasks_off
end
end
document btt
dump all thread stack traces on a kernel compiled with CONFIG_FRAME_POINTER
end
define btpid
set var $pid = $arg0
set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
set $init_t=&init_task
set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
set var $pid_task = 0
while ($next_t != $init_t)
set $next_t=(struct task_struct *)$next_t
if ($next_t.pid == $pid)
set $pid_task = $next_t
end
set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
while ($next_th != $next_t)
set $next_th=(struct task_struct *)$next_th
if ($next_th.pid == $pid)
set $pid_task = $next_th
end
set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
end
set $next_t=(char *)($next_t->tasks.next) - $tasks_off
end
btthreadstack $pid_task
end
document btpid
backtrace of pid
end
define trapinfo
set var $pid = $arg0
set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
set $init_t=&init_task
set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
set var $pid_task = 0
while ($next_t != $init_t)
set $next_t=(struct task_struct *)$next_t
if ($next_t.pid == $pid)
set $pid_task = $next_t
end
set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
while ($next_th != $next_t)
set $next_th=(struct task_struct *)$next_th
if ($next_th.pid == $pid)
set $pid_task = $next_th
end
set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
end
set $next_t=(char *)($next_t->tasks.next) - $tasks_off
end
printf "Trapno %ld, cr2 0x%lx, error_code %ld\n", $pid_task.thread.trap_no, \
$pid_task.thread.cr2, $pid_task.thread.error_code
end
document trapinfo
Run info threads and lookup pid of thread #1
'trapinfo <pid>' will tell you by which trap & possibly
address the kernel panicked.
end
define dump_log_idx
set $idx = $arg0
if ($argc > 1)
set $prev_flags = $arg1
else
set $prev_flags = 0
end
set $msg = ((struct printk_log *) (log_buf + $idx))
set $prefix = 1
set $newline = 1
set $log = log_buf + $idx + sizeof(*$msg)
# prev & LOG_CONT && !(msg->flags & LOG_PREIX)
if (($prev_flags & 8) && !($msg->flags & 4))
set $prefix = 0
end
# msg->flags & LOG_CONT
if ($msg->flags & 8)
# (prev & LOG_CONT && !(prev & LOG_NEWLINE))
if (($prev_flags & 8) && !($prev_flags & 2))
set $prefix = 0
end
# (!(msg->flags & LOG_NEWLINE))
if (!($msg->flags & 2))
set $newline = 0
end
end
if ($prefix)
printf "[%5lu.%06lu] ", $msg->ts_nsec / 1000000000, $msg->ts_nsec % 1000000000
end
if ($msg->text_len != 0)
eval "printf \"%%%d.%ds\", $log", $msg->text_len, $msg->text_len
end
if ($newline)
printf "\n"
end
if ($msg->dict_len > 0)
set $dict = $log + $msg->text_len
set $idx = 0
set $line = 1
while ($idx < $msg->dict_len)
if ($line)
printf " "
set $line = 0
end
set $c = $dict[$idx]
if ($c == '\0')
printf "\n"
set $line = 1
else
if ($c < ' ' || $c >= 127 || $c == '\\')
printf "\\x%02x", $c
else
printf "%c", $c
end
end
set $idx = $idx + 1
end
printf "\n"
end
end
document dump_log_idx
Dump a single log given its index in the log buffer. The first
parameter is the index into log_buf, the second is optional and
specified the previous log buffer's flags, used for properly
formatting continued lines.
end
define dmesg
set $i = log_first_idx
set $end_idx = log_first_idx
set $prev_flags = 0
while (1)
set $msg = ((struct printk_log *) (log_buf + $i))
if ($msg->len == 0)
set $i = 0
else
dump_log_idx $i $prev_flags
set $i = $i + $msg->len
set $prev_flags = $msg->flags
end
if ($i == $end_idx)
loop_break
end
end
end
document dmesg
print the kernel ring buffer
end
Documentation/admin-guide/kdump/index.rst
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================================================================
Documentation for Kdump - The kexec-based Crash Dumping Solution
================================================================
This document includes overview, setup and installation, and analysis
information.
.. toctree::
:maxdepth: 1
kdump
vmcoreinfo
.. only:: subproject and html
Indices
=======
* :ref:`genindex`
Documentation/admin-guide/kdump/kdump.rst
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================================================================
Documentation for Kdump - The kexec-based Crash Dumping Solution
================================================================
This document includes overview, setup and installation, and analysis
information.
Overview
========
Kdump uses kexec to quickly boot to a dump-capture kernel whenever a
dump of the system kernel's memory needs to be taken (for example, when
the system panics). The system kernel's memory image is preserved across
the reboot and is accessible to the dump-capture kernel.
You can use common commands, such as cp and scp, to copy the
memory image to a dump file on the local disk, or across the network to
a remote system.
Kdump and kexec are currently supported on the x86, x86_64, ppc64, ia64,
s390x, arm and arm64 architectures.
When the system kernel boots, it reserves a small section of memory for
the dump-capture kernel. This ensures that ongoing Direct Memory Access
(DMA) from the system kernel does not corrupt the dump-capture kernel.
The kexec -p command loads the dump-capture kernel into this reserved
memory.
On x86 machines, the first 640 KB of physical memory is needed to boot,
regardless of where the kernel loads. Therefore, kexec backs up this
region just before rebooting into the dump-capture kernel.
Similarly on PPC64 machines first 32KB of physical memory is needed for
booting regardless of where the kernel is loaded and to support 64K page
size kexec backs up the first 64KB memory.
For s390x, when kdump is triggered, the crashkernel region is exchanged
with the region [0, crashkernel region size] and then the kdump kernel
runs in [0, crashkernel region size]. Therefore no relocatable kernel is
needed for s390x.
All of the necessary information about the system kernel's core image is
encoded in the ELF format, and stored in a reserved area of memory
before a crash. The physical address of the start of the ELF header is
passed to the dump-capture kernel through the elfcorehdr= boot
parameter. Optionally the size of the ELF header can also be passed
when using the elfcorehdr=[size[KMG]@]offset[KMG] syntax.
With the dump-capture kernel, you can access the memory image through
/proc/vmcore. This exports the dump as an ELF-format file that you can
write out using file copy commands such as cp or scp. Further, you can
use analysis tools such as the GNU Debugger (GDB) and the Crash tool to
debug the dump file. This method ensures that the dump pages are correctly
ordered.
Setup and Installation
======================
Install kexec-tools
-------------------
1) Login as the root user.
2) Download the kexec-tools user-space package from the following URL:
http://kernel.org/pub/linux/utils/kernel/kexec/kexec-tools.tar.gz
This is a symlink to the latest version.
The latest kexec-tools git tree is available at:
- git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
- http://www.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
There is also a gitweb interface available at
http://www.kernel.org/git/?p=utils/kernel/kexec/kexec-tools.git
More information about kexec-tools can be found at
http://horms.net/projects/kexec/
3) Unpack the tarball with the tar command, as follows::
tar xvpzf kexec-tools.tar.gz
4) Change to the kexec-tools directory, as follows::
cd kexec-tools-VERSION
5) Configure the package, as follows::
./configure
6) Compile the package, as follows::
make
7) Install the package, as follows::
make install
Build the system and dump-capture kernels
-----------------------------------------
There are two possible methods of using Kdump.
1) Build a separate custom dump-capture kernel for capturing the
kernel core dump.
2) Or use the system kernel binary itself as dump-capture kernel and there is
no need to build a separate dump-capture kernel. This is possible
only with the architectures which support a relocatable kernel. As
of today, i386, x86_64, ppc64, ia64, arm and arm64 architectures support
relocatable kernel.
Building a relocatable kernel is advantageous from the point of view that
one does not have to build a second kernel for capturing the dump. But
at the same time one might want to build a custom dump capture kernel
suitable to his needs.
Following are the configuration setting required for system and
dump-capture kernels for enabling kdump support.
System kernel config options
----------------------------
1) Enable "kexec system call" in "Processor type and features."::
CONFIG_KEXEC=y
2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo
filesystems." This is usually enabled by default::
CONFIG_SYSFS=y
Note that "sysfs file system support" might not appear in the "Pseudo
filesystems" menu if "Configure standard kernel features (for small
systems)" is not enabled in "General Setup." In this case, check the
.config file itself to ensure that sysfs is turned on, as follows::
grep 'CONFIG_SYSFS' .config
3) Enable "Compile the kernel with debug info" in "Kernel hacking."::
CONFIG_DEBUG_INFO=Y
This causes the kernel to be built with debug symbols. The dump
analysis tools require a vmlinux with debug symbols in order to read
and analyze a dump file.
Dump-capture kernel config options (Arch Independent)
-----------------------------------------------------
1) Enable "kernel crash dumps" support under "Processor type and
features"::
CONFIG_CRASH_DUMP=y
2) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems"::
CONFIG_PROC_VMCORE=y
(CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.)
Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
--------------------------------------------------------------------
1) On i386, enable high memory support under "Processor type and
features"::
CONFIG_HIGHMEM64G=y
or::
CONFIG_HIGHMEM4G
2) On i386 and x86_64, disable symmetric multi-processing support
under "Processor type and features"::
CONFIG_SMP=n
(If CONFIG_SMP=y, then specify maxcpus=1 on the kernel command line
when loading the dump-capture kernel, see section "Load the Dump-capture
Kernel".)
3) If one wants to build and use a relocatable kernel,
Enable "Build a relocatable kernel" support under "Processor type and
features"::
CONFIG_RELOCATABLE=y
4) Use a suitable value for "Physical address where the kernel is
loaded" (under "Processor type and features"). This only appears when
"kernel crash dumps" is enabled. A suitable value depends upon
whether kernel is relocatable or not.
If you are using a relocatable kernel use CONFIG_PHYSICAL_START=0x100000
This will compile the kernel for physical address 1MB, but given the fact
kernel is relocatable, it can be run from any physical address hence
kexec boot loader will load it in memory region reserved for dump-capture
kernel.
Otherwise it should be the start of memory region reserved for
second kernel using boot parameter "crashkernel=Y@X". Here X is
start of memory region reserved for dump-capture kernel.
Generally X is 16MB (0x1000000). So you can set
CONFIG_PHYSICAL_START=0x1000000
5) Make and install the kernel and its modules. DO NOT add this kernel
to the boot loader configuration files.
Dump-capture kernel config options (Arch Dependent, ppc64)
----------------------------------------------------------
1) Enable "Build a kdump crash kernel" support under "Kernel" options::
CONFIG_CRASH_DUMP=y
2) Enable "Build a relocatable kernel" support::
CONFIG_RELOCATABLE=y
Make and install the kernel and its modules.
Dump-capture kernel config options (Arch Dependent, ia64)
----------------------------------------------------------
- No specific options are required to create a dump-capture kernel
for ia64, other than those specified in the arch independent section
above. This means that it is possible to use the system kernel
as a dump-capture kernel if desired.
The crashkernel region can be automatically placed by the system
kernel at run time. This is done by specifying the base address as 0,
or omitting it all together::
crashkernel=256M@0
or::
crashkernel=256M
If the start address is specified, note that the start address of the
kernel will be aligned to 64Mb, so if the start address is not then
any space below the alignment point will be wasted.
Dump-capture kernel config options (Arch Dependent, arm)
----------------------------------------------------------
- To use a relocatable kernel,
Enable "AUTO_ZRELADDR" support under "Boot" options::
AUTO_ZRELADDR=y
Dump-capture kernel config options (Arch Dependent, arm64)
----------------------------------------------------------
- Please note that kvm of the dump-capture kernel will not be enabled
on non-VHE systems even if it is configured. This is because the CPU
will not be reset to EL2 on panic.
Extended crashkernel syntax
===========================
While the "crashkernel=size[@offset]" syntax is sufficient for most
configurations, sometimes it's handy to have the reserved memory dependent
on the value of System RAM -- that's mostly for distributors that pre-setup
the kernel command line to avoid a unbootable system after some memory has
been removed from the machine.
The syntax is::
crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
range=start-[end]
For example::
crashkernel=512M-2G:64M,2G-:128M
This would mean:
1) if the RAM is smaller than 512M, then don't reserve anything
(this is the "rescue" case)
2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
3) if the RAM size is larger than 2G, then reserve 128M
Boot into System Kernel
=======================
1) Update the boot loader (such as grub, yaboot, or lilo) configuration
files as necessary.
2) Boot the system kernel with the boot parameter "crashkernel=Y@X",
where Y specifies how much memory to reserve for the dump-capture kernel
and X specifies the beginning of this reserved memory. For example,
"crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory
starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
On x86 and x86_64, use "crashkernel=64M@16M".
On ppc64, use "crashkernel=128M@32M".
On ia64, 256M@256M is a generous value that typically works.
The region may be automatically placed on ia64, see the
dump-capture kernel config option notes above.
If use sparse memory, the size should be rounded to GRANULE boundaries.
On s390x, typically use "crashkernel=xxM". The value of xx is dependent
on the memory consumption of the kdump system. In general this is not
dependent on the memory size of the production system.
On arm, the use of "crashkernel=Y@X" is no longer necessary; the
kernel will automatically locate the crash kernel image within the
first 512MB of RAM if X is not given.
On arm64, use "crashkernel=Y[@X]". Note that the start address of
the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).
Load the Dump-capture Kernel
============================
After booting to the system kernel, dump-capture kernel needs to be
loaded.
Based on the architecture and type of image (relocatable or not), one
can choose to load the uncompressed vmlinux or compressed bzImage/vmlinuz
of dump-capture kernel. Following is the summary.
For i386 and x86_64:
- Use vmlinux if kernel is not relocatable.
- Use bzImage/vmlinuz if kernel is relocatable.
For ppc64:
- Use vmlinux
For ia64:
- Use vmlinux or vmlinuz.gz
For s390x:
- Use image or bzImage
For arm:
- Use zImage
For arm64:
- Use vmlinux or Image
If you are using an uncompressed vmlinux image then use following command
to load dump-capture kernel::
kexec -p <dump-capture-kernel-vmlinux-image> \
--initrd=<initrd-for-dump-capture-kernel> --args-linux \
--append="root=<root-dev> <arch-specific-options>"
If you are using a compressed bzImage/vmlinuz, then use following command
to load dump-capture kernel::
kexec -p <dump-capture-kernel-bzImage> \
--initrd=<initrd-for-dump-capture-kernel> \
--append="root=<root-dev> <arch-specific-options>"
If you are using a compressed zImage, then use following command
to load dump-capture kernel::
kexec --type zImage -p <dump-capture-kernel-bzImage> \
--initrd=<initrd-for-dump-capture-kernel> \
--dtb=<dtb-for-dump-capture-kernel> \
--append="root=<root-dev> <arch-specific-options>"
If you are using an uncompressed Image, then use following command
to load dump-capture kernel::
kexec -p <dump-capture-kernel-Image> \
--initrd=<initrd-for-dump-capture-kernel> \
--append="root=<root-dev> <arch-specific-options>"
Please note, that --args-linux does not need to be specified for ia64.
It is planned to make this a no-op on that architecture, but for now
it should be omitted
Following are the arch specific command line options to be used while
loading dump-capture kernel.
For i386, x86_64 and ia64:
"1 irqpoll maxcpus=1 reset_devices"
For ppc64:
"1 maxcpus=1 noirqdistrib reset_devices"
For s390x:
"1 maxcpus=1 cgroup_disable=memory"
For arm:
"1 maxcpus=1 reset_devices"
For arm64:
"1 maxcpus=1 reset_devices"
Notes on loading the dump-capture kernel:
* By default, the ELF headers are stored in ELF64 format to support
systems with more than 4GB memory. On i386, kexec automatically checks if
the physical RAM size exceeds the 4 GB limit and if not, uses ELF32.
So, on non-PAE systems, ELF32 is always used.
The --elf32-core-headers option can be used to force the generation of ELF32
headers. This is necessary because GDB currently cannot open vmcore files
with ELF64 headers on 32-bit systems.
* The "irqpoll" boot parameter reduces driver initialization failures
due to shared interrupts in the dump-capture kernel.
* You must specify <root-dev> in the format corresponding to the root
device name in the output of mount command.
* Boot parameter "1" boots the dump-capture kernel into single-user
mode without networking. If you want networking, use "3".
* We generally don't have to bring up a SMP kernel just to capture the
dump. Hence generally it is useful either to build a UP dump-capture
kernel or specify maxcpus=1 option while loading dump-capture kernel.
Note, though maxcpus always works, you had better replace it with
nr_cpus to save memory if supported by the current ARCH, such as x86.
* You should enable multi-cpu support in dump-capture kernel if you intend
to use multi-thread programs with it, such as parallel dump feature of
makedumpfile. Otherwise, the multi-thread program may have a great
performance degradation. To enable multi-cpu support, you should bring up an
SMP dump-capture kernel and specify maxcpus/nr_cpus, disable_cpu_apicid=[X]
options while loading it.
* For s390x there are two kdump modes: If a ELF header is specified with
the elfcorehdr= kernel parameter, it is used by the kdump kernel as it
is done on all other architectures. If no elfcorehdr= kernel parameter is
specified, the s390x kdump kernel dynamically creates the header. The
second mode has the advantage that for CPU and memory hotplug, kdump has
not to be reloaded with kexec_load().
* For s390x systems with many attached devices the "cio_ignore" kernel
parameter should be used for the kdump kernel in order to prevent allocation
of kernel memory for devices that are not relevant for kdump. The same
applies to systems that use SCSI/FCP devices. In that case the
"allow_lun_scan" zfcp module parameter should be set to zero before
setting FCP devices online.
Kernel Panic
============
After successfully loading the dump-capture kernel as previously
described, the system will reboot into the dump-capture kernel if a
system crash is triggered. Trigger points are located in panic(),
die(), die_nmi() and in the sysrq handler (ALT-SysRq-c).
The following conditions will execute a crash trigger point:
If a hard lockup is detected and "NMI watchdog" is configured, the system
will boot into the dump-capture kernel ( die_nmi() ).
If die() is called, and it happens to be a thread with pid 0 or 1, or die()
is called inside interrupt context or die() is called and panic_on_oops is set,
the system will boot into the dump-capture kernel.
On powerpc systems when a soft-reset is generated, die() is called by all cpus
and the system will boot into the dump-capture kernel.
For testing purposes, you can trigger a crash by using "ALT-SysRq-c",
"echo c > /proc/sysrq-trigger" or write a module to force the panic.
Write Out the Dump File
=======================
After the dump-capture kernel is booted, write out the dump file with
the following command::
cp /proc/vmcore <dump-file>
Analysis
========
Before analyzing the dump image, you should reboot into a stable kernel.
You can do limited analysis using GDB on the dump file copied out of
/proc/vmcore. Use the debug vmlinux built with -g and run the following
command::
gdb vmlinux <dump-file>
Stack trace for the task on processor 0, register display, and memory
display work fine.
Note: GDB cannot analyze core files generated in ELF64 format for x86.
On systems with a maximum of 4GB of memory, you can generate
ELF32-format headers using the --elf32-core-headers kernel option on the
dump kernel.
You can also use the Crash utility to analyze dump files in Kdump
format. Crash is available on Dave Anderson's site at the following URL:
http://people.redhat.com/~anderson/
Trigger Kdump on WARN()
=======================
The kernel parameter, panic_on_warn, calls panic() in all WARN() paths. This
will cause a kdump to occur at the panic() call. In cases where a user wants
to specify this during runtime, /proc/sys/kernel/panic_on_warn can be set to 1
to achieve the same behaviour.
Contact
=======
- Vivek Goyal (vgoyal@redhat.com)
- Maneesh Soni (maneesh@in.ibm.com)
GDB macros
==========
.. include:: gdbmacros.txt
:literal:
Documentation/admin-guide/kdump/vmcoreinfo.rst
+488
View File
@@ -0,0 +1,488 @@
==========
VMCOREINFO
==========
What is it?
===========
VMCOREINFO is a special ELF note section. It contains various
information from the kernel like structure size, page size, symbol
values, field offsets, etc. These data are packed into an ELF note
section and used by user-space tools like crash and makedumpfile to
analyze a kernel's memory layout.
Common variables
================
init_uts_ns.name.release
------------------------
The version of the Linux kernel. Used to find the corresponding source
code from which the kernel has been built. For example, crash uses it to
find the corresponding vmlinux in order to process vmcore.
PAGE_SIZE
---------
The size of a page. It is the smallest unit of data used by the memory
management facilities. It is usually 4096 bytes of size and a page is
aligned on 4096 bytes. Used for computing page addresses.
init_uts_ns
-----------
The UTS namespace which is used to isolate two specific elements of the
system that relate to the uname(2) system call. It is named after the
data structure used to store information returned by the uname(2) system
call.
User-space tools can get the kernel name, host name, kernel release
number, kernel version, architecture name and OS type from it.
node_online_map
---------------
An array node_states[N_ONLINE] which represents the set of online nodes
in a system, one bit position per node number. Used to keep track of
which nodes are in the system and online.
swapper_pg_dir
--------------
The global page directory pointer of the kernel. Used to translate
virtual to physical addresses.
_stext
------
Defines the beginning of the text section. In general, _stext indicates
the kernel start address. Used to convert a virtual address from the
direct kernel map to a physical address.
vmap_area_list
--------------
Stores the virtual area list. makedumpfile gets the vmalloc start value
from this variable and its value is necessary for vmalloc translation.
mem_map
-------
Physical addresses are translated to struct pages by treating them as
an index into the mem_map array. Right-shifting a physical address
PAGE_SHIFT bits converts it into a page frame number which is an index
into that mem_map array.
Used to map an address to the corresponding struct page.
contig_page_data
----------------
Makedumpfile gets the pglist_data structure from this symbol, which is
used to describe the memory layout.
User-space tools use this to exclude free pages when dumping memory.
mem_section|(mem_section, NR_SECTION_ROOTS)|(mem_section, section_mem_map)
--------------------------------------------------------------------------
The address of the mem_section array, its length, structure size, and
the section_mem_map offset.
It exists in the sparse memory mapping model, and it is also somewhat
similar to the mem_map variable, both of them are used to translate an
address.
page
----
The size of a page structure. struct page is an important data structure
and it is widely used to compute contiguous memory.
pglist_data
-----------
The size of a pglist_data structure. This value is used to check if the
pglist_data structure is valid. It is also used for checking the memory
type.
zone
----
The size of a zone structure. This value is used to check if the zone
structure has been found. It is also used for excluding free pages.
free_area
---------
The size of a free_area structure. It indicates whether the free_area
structure is valid or not. Useful when excluding free pages.
list_head
---------
The size of a list_head structure. Used when iterating lists in a
post-mortem analysis session.
nodemask_t
----------
The size of a nodemask_t type. Used to compute the number of online
nodes.
(page, flags|_refcount|mapping|lru|_mapcount|private|compound_dtor|compound_order|compound_head)
-------------------------------------------------------------------------------------------------
User-space tools compute their values based on the offset of these
variables. The variables are used when excluding unnecessary pages.
(pglist_data, node_zones|nr_zones|node_mem_map|node_start_pfn|node_spanned_pages|node_id)
-----------------------------------------------------------------------------------------
On NUMA machines, each NUMA node has a pg_data_t to describe its memory
layout. On UMA machines there is a single pglist_data which describes the
whole memory.
These values are used to check the memory type and to compute the
virtual address for memory map.
(zone, free_area|vm_stat|spanned_pages)
---------------------------------------
Each node is divided into a number of blocks called zones which
represent ranges within memory. A zone is described by a structure zone.
User-space tools compute required values based on the offset of these
variables.
(free_area, free_list)
----------------------
Offset of the free_list's member. This value is used to compute the number
of free pages.
Each zone has a free_area structure array called free_area[MAX_ORDER].
The free_list represents a linked list of free page blocks.
(list_head, next|prev)
----------------------
Offsets of the list_head's members. list_head is used to define a
circular linked list. User-space tools need these in order to traverse
lists.
(vmap_area, va_start|list)
--------------------------
Offsets of the vmap_area's members. They carry vmalloc-specific
information. Makedumpfile gets the start address of the vmalloc region
from this.
(zone.free_area, MAX_ORDER)
---------------------------
Free areas descriptor. User-space tools use this value to iterate the
free_area ranges. MAX_ORDER is used by the zone buddy allocator.
log_first_idx
-------------
Index of the first record stored in the buffer log_buf. Used by
user-space tools to read the strings in the log_buf.
log_buf
-------
Console output is written to the ring buffer log_buf at index
log_first_idx. Used to get the kernel log.
log_buf_len
-----------
log_buf's length.
clear_idx
---------
The index that the next printk() record to read after the last clear
command. It indicates the first record after the last SYSLOG_ACTION
_CLEAR, like issued by 'dmesg -c'. Used by user-space tools to dump
the dmesg log.
log_next_idx
------------
The index of the next record to store in the buffer log_buf. Used to
compute the index of the current buffer position.
printk_log
----------
The size of a structure printk_log. Used to compute the size of
messages, and extract dmesg log. It encapsulates header information for
log_buf, such as timestamp, syslog level, etc.
(printk_log, ts_nsec|len|text_len|dict_len)
-------------------------------------------
It represents field offsets in struct printk_log. User space tools
parse it and check whether the values of printk_log's members have been
changed.
(free_area.free_list, MIGRATE_TYPES)
------------------------------------
The number of migrate types for pages. The free_list is described by the
array. Used by tools to compute the number of free pages.
NR_FREE_PAGES
-------------
On linux-2.6.21 or later, the number of free pages is in
vm_stat[NR_FREE_PAGES]. Used to get the number of free pages.
PG_lru|PG_private|PG_swapcache|PG_swapbacked|PG_slab|PG_hwpoision|PG_head_mask
------------------------------------------------------------------------------
Page attributes. These flags are used to filter various unnecessary for
dumping pages.
PAGE_BUDDY_MAPCOUNT_VALUE(~PG_buddy)|PAGE_OFFLINE_MAPCOUNT_VALUE(~PG_offline)
-----------------------------------------------------------------------------
More page attributes. These flags are used to filter various unnecessary for
dumping pages.
HUGETLB_PAGE_DTOR
-----------------
The HUGETLB_PAGE_DTOR flag denotes hugetlbfs pages. Makedumpfile
excludes these pages.
x86_64
======
phys_base
---------
Used to convert the virtual address of an exported kernel symbol to its
corresponding physical address.
init_top_pgt
------------
Used to walk through the whole page table and convert virtual addresses
to physical addresses. The init_top_pgt is somewhat similar to
swapper_pg_dir, but it is only used in x86_64.
pgtable_l5_enabled
------------------
User-space tools need to know whether the crash kernel was in 5-level
paging mode.
node_data
---------
This is a struct pglist_data array and stores all NUMA nodes
information. Makedumpfile gets the pglist_data structure from it.
(node_data, MAX_NUMNODES)
-------------------------
The maximum number of nodes in system.
KERNELOFFSET
------------
The kernel randomization offset. Used to compute the page offset. If
KASLR is disabled, this value is zero.
KERNEL_IMAGE_SIZE
-----------------
Currently unused by Makedumpfile. Used to compute the module virtual
address by Crash.
sme_mask
--------
AMD-specific with SME support: it indicates the secure memory encryption
mask. Makedumpfile tools need to know whether the crash kernel was
encrypted. If SME is enabled in the first kernel, the crash kernel's
page table entries (pgd/pud/pmd/pte) contain the memory encryption
mask. This is used to remove the SME mask and obtain the true physical
address.
Currently, sme_mask stores the value of the C-bit position. If needed,
additional SME-relevant info can be placed in that variable.
For example::
[ misc ][ enc bit ][ other misc SME info ]
0000_0000_0000_0000_1000_0000_0000_0000_0000_0000_..._0000
63 59 55 51 47 43 39 35 31 27 ... 3
x86_32
======
X86_PAE
-------
Denotes whether physical address extensions are enabled. It has the cost
of a higher page table lookup overhead, and also consumes more page
table space per process. Used to check whether PAE was enabled in the
crash kernel when converting virtual addresses to physical addresses.
ia64
====
pgdat_list|(pgdat_list, MAX_NUMNODES)
-------------------------------------
pg_data_t array storing all NUMA nodes information. MAX_NUMNODES
indicates the number of the nodes.
node_memblk|(node_memblk, NR_NODE_MEMBLKS)
------------------------------------------
List of node memory chunks. Filled when parsing the SRAT table to obtain
information about memory nodes. NR_NODE_MEMBLKS indicates the number of
node memory chunks.
These values are used to compute the number of nodes the crashed kernel used.
node_memblk_s|(node_memblk_s, start_paddr)|(node_memblk_s, size)
----------------------------------------------------------------
The size of a struct node_memblk_s and the offsets of the
node_memblk_s's members. Used to compute the number of nodes.
PGTABLE_3|PGTABLE_4
-------------------
User-space tools need to know whether the crash kernel was in 3-level or
4-level paging mode. Used to distinguish the page table.
ARM64
=====
VA_BITS
-------
The maximum number of bits for virtual addresses. Used to compute the
virtual memory ranges.
kimage_voffset
--------------
The offset between the kernel virtual and physical mappings. Used to
translate virtual to physical addresses.
PHYS_OFFSET
-----------
Indicates the physical address of the start of memory. Similar to
kimage_voffset, which is used to translate virtual to physical
addresses.
KERNELOFFSET
------------
The kernel randomization offset. Used to compute the page offset. If
KASLR is disabled, this value is zero.
arm
===
ARM_LPAE
--------
It indicates whether the crash kernel supports large physical address
extensions. Used to translate virtual to physical addresses.
s390
====
lowcore_ptr
-----------
An array with a pointer to the lowcore of every CPU. Used to print the
psw and all registers information.
high_memory
-----------
Used to get the vmalloc_start address from the high_memory symbol.
(lowcore_ptr, NR_CPUS)
----------------------
The maximum number of CPUs.
powerpc
=======
node_data|(node_data, MAX_NUMNODES)
-----------------------------------
See above.
contig_page_data
----------------
See above.
vmemmap_list
------------
The vmemmap_list maintains the entire vmemmap physical mapping. Used
to get vmemmap list count and populated vmemmap regions info. If the
vmemmap address translation information is stored in the crash kernel,
it is used to translate vmemmap kernel virtual addresses.
mmu_vmemmap_psize
-----------------
The size of a page. Used to translate virtual to physical addresses.
mmu_psize_defs
--------------
Page size definitions, i.e. 4k, 64k, or 16M.
Used to make vtop translations.
vmemmap_backing|(vmemmap_backing, list)|(vmemmap_backing, phys)|(vmemmap_backing, virt_addr)
--------------------------------------------------------------------------------------------
The vmemmap virtual address space management does not have a traditional
page table to track which virtual struct pages are backed by a physical
mapping. The virtual to physical mappings are tracked in a simple linked
list format.
User-space tools need to know the offset of list, phys and virt_addr
when computing the count of vmemmap regions.
mmu_psize_def|(mmu_psize_def, shift)
------------------------------------
The size of a struct mmu_psize_def and the offset of mmu_psize_def's
member.
Used in vtop translations.
sh
==
node_data|(node_data, MAX_NUMNODES)
-----------------------------------
See above.
X2TLB
-----
Indicates whether the crashed kernel enabled SH extended mode.