kmemdump is a mechanism which allows the kernel to mark specific memory areas for dumping or specific backend usage. Once regions are marked, kmemdump keeps an internal list with the regions and registers them in the backend. Further, depending on the backend driver, these regions can be dumped using firmware or different hardware block. Regions being marked beforehand, when the system is up and running, there is no need nor dependency on a panic handler, or a working kernel that can dump the debug information. The kmemdump approach works when pstore, kdump, or another mechanism do not. Pstore relies on persistent storage, a dedicated RAM area or flash, which has the disadvantage of having the memory reserved all the time, or another specific non volatile memory. Some devices cannot keep the RAM contents on reboot so ramoops does not work. Some devices do not allow kexec to run another kernel to debug the crashed one. For such devices, that have another mechanism to help debugging, like firmware, kmemdump is a viable solution. kmemdump can create a core image, similar with /proc/vmcore, with only the registered regions included. This can be loaded into crash tool/gdb and analyzed. To have this working, specific information from the kernel is registered, and this is done at kmemdump init time, no need for the kmemdump user to do anything. The implementation is based on the initial Pstore/directly mapped zones published as an RFC here: https://lore.kernel.org/all/20250217101706.2104498-1-eugen.hristev@xxxxxxxxxx/ The back-end implementation for qcom_smem is based on the minidump patch series and driver written by Mukesh Ojha, thanks: https://lore.kernel.org/lkml/20240131110837.14218-1-quic_mojha@xxxxxxxxxxx/ I appreciate the feedback on this series, I know it is a longshot, and there is a lot to improve, but I hope I am on the right track. Thanks, Eugen PS. Here is how crash tool reports the dump: KERNEL: /home/eugen/linux-minidump/vmlinux [TAINTED] DUMPFILE: /home/eugen/eee CPUS: 8 [OFFLINE: 7] DATE: Thu Jan 1 02:00:00 EET 1970 UPTIME: 00:00:28 NODENAME: qemuarm64 RELEASE: 6.14.0-rc5-next-20250303-00014-g011eb2aaf7b6-dirty VERSION: #169 SMP PREEMPT Thu Apr 17 14:12:21 EEST 2025 MACHINE: aarch64 (unknown Mhz) MEMORY: 0 PANIC: "" crash> log [ 0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd4b2] [ 0.000000] Linux version 6.14.0-rc5-next-20250303-00014-g011eb2aaf7b6-dirty (eugen@eugen-station) (aarch64-none-linux-gnu-gcc (Arm GNU Toolchain 13.3.Rel1 (Build arm-13.24)) 13.3.1 20240614, GNU ld (Arm GNU Toolchain 13.3.Rel1 (Build arm-13.24)) 2.42.0.20240614) #169 SMP PREEMPT Thu Apr 17 14:12:21 EEST 2025 [ 0.000000] KASLR enabled [...] Eugen Hristev (14): Documentation: add kmemdump kmemdump: introduce kmemdump kmemdump: introduce qcom-md backend driver soc: qcom: smem: add minidump device Documentation: kmemdump: add section for coreimage ELF kmemdump: add coreimage ELF layer printk: add kmsg_kmemdump_register kmemdump: coreimage: add kmsg registration genirq: add irq_kmemdump_register kmemdump: coreimage: add irq registration panic: add panic_kmemdump_register kmemdump: coreimage: add panic registration sched: add sched_kmemdump_register kmemdump: coreimage: add sched registration Documentation/debug/index.rst | 17 ++ Documentation/debug/kmemdump.rst | 83 +++++ drivers/Kconfig | 2 + drivers/Makefile | 2 + drivers/debug/Kconfig | 39 +++ drivers/debug/Makefile | 5 + drivers/debug/kmemdump.c | 197 ++++++++++++ drivers/debug/kmemdump_coreimage.c | 293 ++++++++++++++++++ drivers/debug/qcom_md.c | 467 +++++++++++++++++++++++++++++ drivers/soc/qcom/smem.c | 10 + include/linux/irqnr.h | 1 + include/linux/kmemdump.h | 77 +++++ include/linux/kmsg_dump.h | 6 + include/linux/panic.h | 1 + include/linux/sched.h | 1 + kernel/irq/irqdesc.c | 7 + kernel/panic.c | 8 + kernel/printk/printk.c | 13 + kernel/sched/core.c | 7 + 19 files changed, 1236 insertions(+) create mode 100644 Documentation/debug/index.rst create mode 100644 Documentation/debug/kmemdump.rst create mode 100644 drivers/debug/Kconfig create mode 100644 drivers/debug/Makefile create mode 100644 drivers/debug/kmemdump.c create mode 100644 drivers/debug/kmemdump_coreimage.c create mode 100644 drivers/debug/qcom_md.c create mode 100644 include/linux/kmemdump.h -- 2.43.0
