Documentation/admin-guide/ramoops.rst

9 ------------
11 Ramoops is an oops/panic logger that writes its logs to RAM before the system
13 needs a system with persistent RAM so that the content of that area can
17 ----------------
54 to life (i.e. a watchdog triggered). In such cases, RAM may be somewhat
58 ----------------------
66  the kernel to use only the first 128 MB of memory, and place ECC-protected
72  ``Documentation/devicetree/bindings/reserved-memory/ramoops.yaml``.
75 	reserved-memory {
76 		#address-cells = <2>;
77 		#size-cells = <2>;
83 			record-size = <0x4000>;
84 			console-size = <0x4000>;
91  .. code-block:: c
121 You can specify either RAM memory or peripheral devices' memory. However, when
122 specifying RAM, be sure to reserve the memory by issuing memblock_reserve()
123 very early in the architecture code, e.g.::
130 -----------
136 ----------------
139 files is ``dmesg-ramoops-N``, where N is the record number in memory. To delete
140 a stored record from RAM, simply unlink the respective pstore file.
143 ---------------------------
146 related hangs. The functions call chain log is stored in a ``ftrace-ramoops``
149  # mount -t debugfs debugfs /sys/kernel/debug/
151  # reboot -f
153  # mount -t pstore pstore /mnt/
154  # tail /mnt/ftrace-ramoops
155  0 ffffffff8101ea64  ffffffff8101bcda  native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0
156  0 ffffffff8101ea44  ffffffff8101bcf6  native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0
157  0 ffffffff81020084  ffffffff8101a4b5  hpet_disable <- native_machine_shutdown+0x75/0x90
158  0 ffffffff81005f94  ffffffff8101a4bb  iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90
159 …0 ffffffff8101a6a1  ffffffff8101a437  native_machine_emergency_restart <- native_machine_restart+0…
160  0 ffffffff811f9876  ffffffff8101a73a  acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0
161 …0 ffffffff8101a514  ffffffff8101a772  mach_reboot_fixups <- native_machine_emergency_restart+0xe2/…
162 …0 ffffffff811d9c54  ffffffff8101a7a0  __const_udelay <- native_machine_emergency_restart+0x110/0x1…
163  0 ffffffff811d9c34  ffffffff811d9c80  __delay <- __const_udelay+0x30/0x40
164  0 ffffffff811d9d14  ffffffff811d9c3f  delay_tsc <- __delay+0xf/0x20