Documentation/admin-guide/ramoops.rst

Source file repositories/reference/linux-study-clean/Documentation/admin-guide/ramoops.rst

File Facts

System
Linux kernel
Corpus path
Documentation/admin-guide/ramoops.rst
Extension
.rst
Size
7102 bytes
Lines
178
Domain
Support Tooling And Documentation
Bucket
Documentation
Inferred role
Support Tooling And Documentation: documentation
Status
atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

if (ret) {
	printk(KERN_ERR "unable to register platform device\n");
	return ret;
  }

 D. Using a region of memory reserved via ``reserve_mem`` command line
    parameter. The address and size will be defined by the ``reserve_mem``
    parameter. Note, that ``reserve_mem`` may not always allocate memory
    in the same location, and cannot be relied upon. Testing will need
    to be done, and it may not work on every machine, nor every kernel.
    Consider this a "best effort" approach. The ``reserve_mem`` option
    takes a size, alignment and name as arguments. The name is used
    to map the memory to a label that can be retrieved by ramoops.

	reserve_mem=2M:4096:oops  ramoops.mem_name=oops

You can specify either RAM memory or peripheral devices' memory. However, when
specifying RAM, be sure to reserve the memory by issuing memblock_reserve()
very early in the architecture code, e.g.::

	#include <linux/memblock.h>

	memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size);

Dump format
-----------

The data dump begins with a header, currently defined as ``====`` followed by a
timestamp and a new line. The dump then continues with the actual data.

Reading the data
----------------

The dump data can be read from the pstore filesystem. The format for these
files is ``dmesg-ramoops-N``, where N is the record number in memory. To delete
a stored record from RAM, simply unlink the respective pstore file.

Persistent function tracing
---------------------------

Persistent function tracing might be useful for debugging software or hardware
related hangs. The functions call chain log is stored in a ``ftrace-ramoops``
file. Here is an example of usage::

 # mount -t debugfs debugfs /sys/kernel/debug/
 # echo 1 > /sys/kernel/debug/pstore/record_ftrace
 # reboot -f
 [...]
 # mount -t pstore pstore /mnt/
 # tail /mnt/ftrace-ramoops
 0 ffffffff8101ea64  ffffffff8101bcda  native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0
 0 ffffffff8101ea44  ffffffff8101bcf6  native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0
 0 ffffffff81020084  ffffffff8101a4b5  hpet_disable <- native_machine_shutdown+0x75/0x90
 0 ffffffff81005f94  ffffffff8101a4bb  iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90
 0 ffffffff8101a6a1  ffffffff8101a437  native_machine_emergency_restart <- native_machine_restart+0x37/0x40
 0 ffffffff811f9876  ffffffff8101a73a  acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0
 0 ffffffff8101a514  ffffffff8101a772  mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0
 0 ffffffff811d9c54  ffffffff8101a7a0  __const_udelay <- native_machine_emergency_restart+0x110/0x1e0
 0 ffffffff811d9c34  ffffffff811d9c80  __delay <- __const_udelay+0x30/0x40
 0 ffffffff811d9d14  ffffffff811d9c3f  delay_tsc <- __delay+0xf/0x20

Annotation

Implementation Notes