how to use kexec to jump back to the original kernel

[Gioh Kim]

Hello,

"echo c > /proc/sysrq-trigger" generates the kernel dump but it
reboots the system.
I'd like to generate kernel dump without system reboot.

I think it is possible to jump to the kdump kernel and generate kernel
dump, and come back to the operating kernel with kexec.
I know I can jump to the kdump kernel with "kexec -e" but I cannot
figure out how to come back to the operating kernel.

For example, I tried following sequences after reading kexec manual page.

0. rebuild kernel with CONFIG_KEXEC_JUMP option
1. kexec --load=/boot/vmlinuz --initrd=/boot/initrd --reuse-cmdline
2. kexec -e
3. now kdump kernel is running
4. kexec --load-jump-back-helper --entry=<ADDRESS>
5. kexec -e

I can jump to the kdump kernel with step 1 and step 2.
kexec manual says I need an entry address.
I don't know what address I should use.
I found a email thread about jump_back_entry= but there is no
parameter like jump_back_entry in kernel booting parameters of
v4.4~v4.14.

Does anybody know how to use kexec to jump between kdump kernel and
operating kernel?


-- 

Best regards,
Gioh Kim