The --command-line, --append, and --reuse-cmdline options to kexec can
be used in combination to craft a kernel command line for a kernel
loaded via kexec. In addition, the kexec tool may also manipulate
further the command line, eg. elfcorehdr addition.
To aid in debugging kdump/kexec related issues, it would be helpful
for kexec to print the final constructed kernel command line argument.
For example, the following simple change (for i386/x86_64):
diff --git a/kexec/arch/i386/x86-linux-setup.c b/kexec/arch/i386/x86-linux-setup.c
index 057ee14..6dc4adc 100644
--- a/kexec/arch/i386/x86-linux-setup.c
+++ b/kexec/arch/i386/x86-linux-setup.c
@@ -57,6 +57,8 @@ void setup_linux_bootloader_parameters_high(
char *cmdline_ptr;
unsigned long initrd_base, initrd_addr_max;
+ printf("Final kernel cmdline: '%s'\n", cmdline);
+
/* Say I'm a boot loader */
real_mode->loader_type = LOADER_TYPE_KEXEC << 4;
results in the following on a systemd-based system (formatted to fit
in 70 char lines):
% systemctl status -l kdump.service
● kdump.service - Crash recovery kernel arming
Loaded: loaded (/usr/lib/systemd/system/kdump.service; enabled;
vendor preset: enabled)
Active: active (exited) since Mon 2019-12-16 14:59:21 EST;
2min 53s ago
Process: 14058 ExecStop=/usr/bin/kdumpctl stop (code=exited,
status=0/SUCCESS)
Process: 14073 ExecStart=/usr/bin/kdumpctl start (code=exited,
status=0/SUCCESS)
Main PID: 14073 (code=exited, status=0/SUCCESS)
Dec 16 14:59:18 vm364 kdumpctl[14058]: Stopping kdump: [OK]
Dec 16 14:59:18 vm364 systemd[1]: Stopped Crash recovery kernel arming.
Dec 16 14:59:18 vm364 systemd[1]: Starting Crash recovery kernel arming...
Dec 16 14:59:21 vm364 kdumpctl[14073]: Final kernel cmdline: 'BOOT_IMAGE=
/vmlinuz-4.14.35-1902.7.3.1.el7uek.x86_64 ro rhgb quiet LANG=en_US.UTF-8
irqpoll nr_cpus=1 reset_devices cgroup_disable=memory mce=off numa=off
udev.children-max=2 panic=10 rootflags=nofail acpi_no_memhotplug
transparent_hugepage=never nokaslr novmcoredd disable_cpu_apicid=0
elfcorehdr=901492K'
Dec 16 14:59:21 vm364 systemd[1]: Started Crash recovery kernel arming.
Dec 16 14:59:21 vm364 kdumpctl[14073]: kexec: loaded kdump kernel
Dec 16 14:59:21 vm364 kdumpctl[14073]: Starting kdump: [OK]
and the output is also available in /var/log/messages.
There might also be an opportunity to consolidate handling of the
kernel command line, as most arch targets have the --command-line,
--append, and --reuse-cmdline options, though each arch independently
codes the support for these options.
Note: Simply printing the cmdline in scripts such as kdumpctl may not
result in the same ordering, and will omit any addition made internally
by kexec, such as the elfcorehdr.
I propose the addition of an option to kexec, --print-kcl (to mirror
--print-ckr), that would control such printing, as well as the needed
per arch conditional print statements similar to the above to print the
final constructed kernel command line.
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