Linux PStore and Ramoops modules (Linux config options PSTORE and PSTORE_RAM) allow to use memory to pass data from the dying breath of a crashing kernel to its successor. This command allows to read those records from U-Boot command line.
Ramoops is an oops/panic logger that writes its logs to RAM before the system crashes. It works by logging oopses and panics in a circular buffer. Ramoops needs a system with persistent RAM so that the content of that area can survive after a restart.
Ramoops uses a predefined memory area to store the dump.
Ramoops parameters can be passed as kernel parameters or through Device Tree, i.e.:
ramoops.mem_address=0x30000000 ramoops.mem_size=0x100000 ramoops.record_size=0x2000 ramoops.console_size=0x2000 memmap=0x100000$0x30000000
The same values should be set in U-Boot to be able to retrieve the records. This values can be set at build time in U-Boot configuration file, or at runtime. U-Boot automatically patches the Device Tree to pass the Ramoops parameters to the kernel.
The PStore configuration parameters are:
Records sizes should be a power of 2. The memory size and the record/console size must be non-zero.
Multiple ‘dump’ records can be stored in the memory reserved for PStore. The memory size has to be larger than the sum of the record sizes, i.e.:
MEM_SIZE >= RECORD_SIZE * n + CONSOLE_SIZE + FTRACE_SIZE + PMSG_SIZE
Generate kernel crash¶
For test purpose, you can generate a kernel crash by setting reboot timeout to 10 seconds and trigger a panic:
$ sudo sh -c "echo 1 > /proc/sys/kernel/sysrq" $ sudo sh -c "echo 10 > /proc/sys/kernel/panic" $ sudo sh -c "echo c > /proc/sysrq-trigger"
Retrieve logs in U-Boot¶
First of all, unless PStore parameters as been set during U-Boot configuration and match kernel ramoops parameters, it needs to be set using ‘pstore set’, e.g.:
=> pstore set 0x30000000 0x100000 0x2000 0x2000
Then all available dumps can be displayed using:
=> pstore display
Or saved to an existing directory in an Ext2 or Ext4 partition, e.g. on root directory of 1st partition of the 2nd MMC:
=> pstore save mmc 1:1 /