EFISTUB: If I have both CMDLINE configured in kernel, AND via efibootmgr, which one gets executed / takes precedence?

suppose I enable CONFIG_CMDLINE_BOOL=y and CONFIG_CMDLINE=“…”, but I also add a cmdline using efibootmgr via -u option, which one takes precedence and gets executed?

Does an initramfs make this more complicated? does it also have its own cmdline?

blobjim , 11 months ago
Looking in git.kernel.org/pub/scm/linux/kernel/git/…/main.c?… there’s a function setup_command_line that seems to set up the built-in command line which is called after setup_boot_config

ok idk what that all was. Here’s something more interesting:

In arch/x86/kernel/setup.c it says /* append boot loader cmdline to builtin */. I think that suggests that the builtin comes first. And I assume that the code that queries the command line scans left to right and selects the first instance of an option because there doesn’t seem to be anywhere that “loads” args into some kind of structure.

git.kernel.org/pub/scm/linux/kernel/…/setup.c?h=v…
#ifdef CONFIG_CMDLINE_BOOL
#ifdef CONFIG_CMDLINE_OVERRIDE
	strscpy(boot_command_line, builtin_cmdline, COMMAND_LINE_SIZE);
#else
	if (builtin_cmdline[0]) {
		/* append boot loader cmdline to builtin */
		strlcat(builtin_cmdline, " ", COMMAND_LINE_SIZE);
		strlcat(builtin_cmdline, boot_command_line, COMMAND_LINE_SIZE);
		strscpy(boot_command_line, builtin_cmdline, COMMAND_LINE_SIZE);
	}
#endif
#endif

I guess the best thing to do would be to run linux in QEMU with the EFI system that’s provided by a third party thing and test it out.
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Gobbel2000 , 11 months ago

In arch/x86/Kconfig of the kernel tree it says for CMDLINE:


<span style="color:#323232;">	  Enter arguments here that should be compiled into the kernel
</span><span style="color:#323232;">	  image and used at boot time.  If the boot loader provides a
</span><span style="color:#323232;">	  command line at boot time, it is appended to this string to
</span><span style="color:#323232;">	  form the full kernel command line, when the system boots.
</span><span style="color:#323232;">
</span><span style="color:#323232;">	  However, you can use the CONFIG_CMDLINE_OVERRIDE option to
</span><span style="color:#323232;">	  change this behavior.
</span><span style="color:#323232;">
</span><span style="color:#323232;">	  In most cases, the command line (whether built-in or provided
</span><span style="color:#323232;">	  by the boot loader) should specify the device for the root
</span><span style="color:#323232;">	  file system.
</span>

and for CMDLINE_OVERRIDE:


<span style="color:#323232;">	  Set this option to 'Y' to have the kernel ignore the boot loader
</span><span style="color:#323232;">	  command line, and use ONLY the built-in command line.
</span><span style="color:#323232;">
</span><span style="color:#323232;">	  This is used to work around broken boot loaders.  This should
</span><span style="color:#323232;">	  be set to 'N' under normal conditions.
</span>

So both commandlines will probably be used. I don’t think an initramfs will normally interfere with the kernel commandline. In any case you can make sure you got what you wanted with cat /proc/cmdline.