1 Ramoops oops/panic logger
2 =========================
4 Sergiu Iordache <sergiu@chromium.org>
6 Updated: 17 November 2011
10 Ramoops is an oops/panic logger that writes its logs to RAM before the system
11 crashes. It works by logging oopses and panics in a circular buffer. Ramoops
12 needs a system with persistent RAM so that the content of that area can
13 survive after a restart.
17 Ramoops uses a predefined memory area to store the dump. The start and size of
18 the memory area are set using two variables:
19 * "mem_address" for the start
20 * "mem_size" for the size. The memory size will be rounded down to a
23 The memory area is divided into "record_size" chunks (also rounded down to
24 power of two) and each oops/panic writes a "record_size" chunk of
27 Dumping both oopses and panics can be done by setting 1 in the "dump_oops"
28 variable while setting 0 in that variable dumps only the panics.
30 The module uses a counter to record multiple dumps but the counter gets reset
31 on restart (i.e. new dumps after the restart will overwrite old ones).
33 Ramoops also supports software ECC protection of persistent memory regions.
34 This might be useful when a hardware reset was used to bring the machine back
35 to life (i.e. a watchdog triggered). In such cases, RAM may be somewhat
36 corrupt, but usually it is restorable.
38 2. Setting the parameters
40 Setting the ramoops parameters can be done in 2 different manners:
41 1. Use the module parameters (which have the names of the variables described
43 For quick debugging, you can also reserve parts of memory during boot
44 and then use the reserved memory for ramoops. For example, assuming a machine
45 with > 128 MB of memory, the following kernel command line will tell the
46 kernel to use only the first 128 MB of memory, and place ECC-protected ramoops
47 region at 128 MB boundary:
48 "mem=128M ramoops.mem_address=0x8000000 ramoops.ecc=1"
49 2. Use a platform device and set the platform data. The parameters can then
50 be set through that platform data. An example of doing that is:
52 #include <linux/pstore_ram.h>
55 static struct ramoops_platform_data ramoops_data = {
63 static struct platform_device ramoops_dev = {
66 .platform_data = &ramoops_data,
70 [... inside a function ...]
73 ret = platform_device_register(&ramoops_dev);
75 printk(KERN_ERR "unable to register platform device\n");
79 You can specify either RAM memory or peripheral devices' memory. However, when
80 specifying RAM, be sure to reserve the memory by issuing memblock_reserve()
81 very early in the architecture code, e.g.:
83 #include <linux/memblock.h>
85 memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size);
89 The data dump begins with a header, currently defined as "====" followed by a
90 timestamp and a new line. The dump then continues with the actual data.
94 The dump data can be read from the pstore filesystem. The format for these
95 files is "dmesg-ramoops-N", where N is the record number in memory. To delete
96 a stored record from RAM, simply unlink the respective pstore file.
98 5. Persistent function tracing
100 Persistent function tracing might be useful for debugging software or hardware
101 related hangs. The functions call chain log is stored in a "ftrace-ramoops"
102 file. Here is an example of usage:
104 # mount -t debugfs debugfs /sys/kernel/debug/
105 # echo 1 > /sys/kernel/debug/pstore/record_ftrace
108 # mount -t pstore pstore /mnt/
109 # tail /mnt/ftrace-ramoops
110 0 ffffffff8101ea64 ffffffff8101bcda native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0
111 0 ffffffff8101ea44 ffffffff8101bcf6 native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0
112 0 ffffffff81020084 ffffffff8101a4b5 hpet_disable <- native_machine_shutdown+0x75/0x90
113 0 ffffffff81005f94 ffffffff8101a4bb iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90
114 0 ffffffff8101a6a1 ffffffff8101a437 native_machine_emergency_restart <- native_machine_restart+0x37/0x40
115 0 ffffffff811f9876 ffffffff8101a73a acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0
116 0 ffffffff8101a514 ffffffff8101a772 mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0
117 0 ffffffff811d9c54 ffffffff8101a7a0 __const_udelay <- native_machine_emergency_restart+0x110/0x1e0
118 0 ffffffff811d9c34 ffffffff811d9c80 __delay <- __const_udelay+0x30/0x40
119 0 ffffffff811d9d14 ffffffff811d9c3f delay_tsc <- __delay+0xf/0x20