Re: [PATCH v2 6/6] x86/setup: prepend embedded bootconfig cmdline before parse_early_param

[Breno Leitao <leitao@debian.org>]

On Mon, Jun 08, 2026 at 07:19:28PM +0900, Masami Hiramatsu wrote:
> On Fri, 05 Jun 2026 05:03:37 -0700
> Breno Leitao <leitao@debian.org> wrote:
> 
> > Call xbc_prepend_embedded_cmdline() in setup_arch() right after the
> > CONFIG_CMDLINE merge and before strscpy(command_line, ...) so the
> > build-time-rendered embedded bootconfig "kernel" subtree is part of
> > boot_command_line by the time parse_early_param() runs. early_param()
> > handlers (mem=, earlycon=, loglevel=, ...) now see values supplied via
> > CONFIG_BOOT_CONFIG_EMBED_FILE without parsing bootconfig at runtime.
> > 
> > Gate the prepend on the bootconfig opt-in: only fold in the embedded
> > kernel.* keys when "bootconfig" is present on the command line, or
> > CONFIG_BOOT_CONFIG_FORCE is set. Applying the embedded cmdline
> > unconditionally would (a) diverge from how embedded init.* keys are
> > treated and (b) break fail-safe recovery: a malformed embedded
> > console=/mem= could panic the boot with no way for the admin to disable
> > it by dropping "bootconfig" from the bootloader cmdline.
> > cmdline_find_option_bool() runs before parse_early_param(), so the gate
> > is cheap and correctly ordered.
> > 
> > Select ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG so the user-visible
> > CONFIG_BOOT_CONFIG_EMBED_CMDLINE option becomes selectable on x86.
> 
> This seems like a dummy config. what code does depend on this flag?

No C code reads ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG directly — it's
a silent gating symbol, the same ARCH_SUPPORTS_* idiom as
ARCH_SUPPORTS_CFI, ARCH_SUPPORTS_LTO_CLANG, etc.

Its only role is the depends on line of BOOT_CONFIG_EMBED_CMDLINE: an
arch selects it once its setup_arch() calls
xbc_prepend_embedded_cmdline(), and that makes the user-visible
BOOT_CONFIG_EMBED_CMDLINE selectable.

Right now, only x86 supports embedded bootconfig, thus, only x86 does
the following (last patch):

	config X86
	+       select ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG

So, no other platform can see CONFIG_BOOT_CONFIG_EMBED_CMDLINE.

> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -378,12 +378,15 @@ static void __init setup_boot_config(void)
> >  	int pos, ret;
> >  	size_t size;
> >  	char *err;
> > +	bool from_embedded = false;
> >  
> >  	/* Cut out the bootconfig data even if we have no bootconfig option */
> >  	data = get_boot_config_from_initrd(&size);
> >  	/* If there is no bootconfig in initrd, try embedded one. */
> > -	if (!data)
> > +	if (!data) {
> >  		data = xbc_get_embedded_bootconfig(&size);
> > +		from_embedded = true;
> 
> Even from embedded bootconfig, if the arch set 
> ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG=n, this must be applied to
> the cmdline as we are doing.

Right — that path is preserved. When the arch doesn't select
ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG, BOOT_CONFIG_EMBED_CMDLINE is
unselectable, so xbc_embedded_cmdline_applied() is the no-op stub
returning false.

> >  	strscpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
> >  	err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
> > @@ -421,8 +424,17 @@ static void __init setup_boot_config(void)
> >  	} else {
> >  		xbc_get_info(&ret, NULL);
> >  		pr_info("Load bootconfig: %ld bytes %d nodes\n", (long)size, ret);
> > -		/* keys starting with "kernel." are passed via cmdline */
> > -		extra_command_line = xbc_make_cmdline("kernel");
> > +		/*
> > +		 * keys starting with "kernel." are passed via cmdline. When
> > +		 * this bootconfig came from the embedded source and
> > +		 * setup_arch() already prepended the rendered "kernel" subtree
> > +		 * to boot_command_line, rendering again here would duplicate
> > +		 * the keys in saved_command_line and make accumulating handlers
> > +		 * (console=, earlycon=, ...) re-register the same value. Skip
> > +		 * only when the prepend really happened.
> 
> Also, this should mention ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG=n case.

Ack, I will update

Thanks for the review,
--breno