Re: [PATCH v6 8/8] x86/setup: prepend embedded bootconfig cmdline before parse_early_param

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Tue, 23 Jun 2026 09:15:35 -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 same opt-in the runtime parser uses: prepend
> when "bootconfig" is present on the command line, or when
> CONFIG_BOOT_CONFIG_FORCE is set. Detect it with parse_args(), exactly
> as setup_boot_config() does, so both agree on what counts as opt-in:
> any "bootconfig" key regardless of value (bare, =0, =1, ...), and only
> before the "--" that separates init arguments. Sharing the parser keeps
> the early and late paths from diverging -- e.g. "bootconfig=0" or a
> "-- bootconfig" meant for init must not apply the embedded keys early
> while the runtime parser skips them.
> 
> The prepend necessarily runs before setup_boot_config() detects an
> initrd bootconfig, so an initrd cannot override the embedded "kernel"
> keys for early_param(). This is intentional: the embedded cmdline acts
> like a build-time CONFIG_CMDLINE. An initrd bootconfig's "kernel" keys
> never reached early_param() anyway (they apply late via
> extra_command_line), so nothing is lost -- the initrd keys still apply
> late, with last-wins keeping the embedded values in effect.
> 
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  arch/x86/Kconfig        |  1 +
>  arch/x86/kernel/setup.c | 43 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 44 insertions(+)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 0de23e6471973..8ab11199c16d5 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -127,6 +127,7 @@ config X86
>  	select ARCH_SUPPORTS_NUMA_BALANCING	if X86_64
>  	select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP	if NR_CPUS <= 4096
>  	select ARCH_SUPPORTS_CFI		if X86_64
> +	select ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG
>  	select ARCH_USES_CFI_TRAPS		if X86_64 && CFI
>  	select ARCH_SUPPORTS_LTO_CLANG
>  	select ARCH_SUPPORTS_LTO_CLANG_THIN
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 46882ce79c3a4..c973a2cebcd04 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -6,6 +6,7 @@
>   * parts of early kernel initialization.
>   */
>  #include <linux/acpi.h>
> +#include <linux/bootconfig.h>
>  #include <linux/console.h>
>  #include <linux/cpu.h>
>  #include <linux/crash_dump.h>
> @@ -881,6 +882,37 @@ static void __init x86_report_nx(void)
>   * Note: On x86_64, fixmaps are ready for use even before this is called.
>   */
>  
> +#ifdef CONFIG_CMDLINE_FROM_BOOTCONFIG
> +static int __init bootconfig_optin(char *param, char *val,
> +				   const char *unused, void *arg)
> +{
> +	if (!strcmp(param, "bootconfig"))
> +		*(bool *)arg = true;
> +	return 0;
> +}
> +
> +/*
> + * Did the user opt in to bootconfig on the kernel command line? Use
> + * parse_args() so this matches setup_boot_config() exactly, including
> + * stopping at the "--" that separates init arguments.
> + */
> +static bool __init bootconfig_cmdline_requested(void)
> +{
> +	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
> +	bool found = false;
> +
> +	if (IS_ENABLED(CONFIG_BOOT_CONFIG_FORCE))
> +		return true;
> +
> +	strscpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
> +	if (IS_ERR(parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0,
> +			      &found, bootconfig_optin)))
> +		return false;
> +
> +	return found;
> +}

It seems that this should be placed in a common place because it will
be used from other architectures (and init/main.c too). Maybe we can
introduce something like this?

bool __init bootconfig_cmdline_requested(const char *boot_cmdline, int *end_offset);

Thanks,

> +#endif
> +
>  void __init setup_arch(char **cmdline_p)
>  {
>  #ifdef CONFIG_X86_32
> @@ -924,6 +956,17 @@ void __init setup_arch(char **cmdline_p)
>  	builtin_cmdline_added = true;
>  #endif
>  
> +#ifdef CONFIG_CMDLINE_FROM_BOOTCONFIG
> +	/*
> +	 * Prepend the build-time-rendered embedded "kernel" keys here so
> +	 * parse_early_param() below sees them, gating on the same opt-in
> +	 * as the runtime parser (see bootconfig_cmdline_requested()).
> +	 */
> +	if (bootconfig_cmdline_requested())
> +		xbc_prepend_embedded_cmdline(boot_command_line,
> +					     COMMAND_LINE_SIZE);
> +#endif
> +
>  	strscpy(command_line, boot_command_line, COMMAND_LINE_SIZE);
>  	*cmdline_p = command_line;
>  
> 
> -- 
> 2.53.0-Meta
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>