[PATCH 0/4] bootconfig: embed kernel.* cmdline at build time

[PATCH 0/4] bootconfig: embed kernel.* cmdline at build time

[Breno Leitao]

The userspace pieces (xbc_snprint_cmdline() in lib/, tools/bootconfig -C)
already landed; this series wires the rendered cmdline into the kernel.

Motivation: today the embedded bootconfig is parsed at runtime, after
parse_early_param() has already run, so early_param() handlers can't
see embedded values. Folding the kernel.* subtree into the cmdline at
build time gives a CONFIG_CMDLINE-equivalent for embedded-bootconfig
users without forcing them to maintain two cmdline sources.

Behaviorally, the "kernel" subtree is rendered to a flat string at
build time and stashed in .init.rodata. setup_arch() prepends it to
boot_command_line before parse_early_param() runs. Overflow is a soft
error: the helper logs and leaves boot_command_line untouched rather
than panicking, so an oversized embedded bconf cannot brick a boot.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
Breno Leitao (4):
      bootconfig: return 0 from xbc_snprint_cmdline() for a leaf root
      bootconfig: render embedded bootconfig as a kernel cmdline at build time
      bootconfig: add xbc_prepend_embedded_cmdline() helper
      x86/setup: prepend embedded bootconfig cmdline before parse_early_param

 Makefile                   |  5 ++++
 arch/x86/Kconfig           |  1 +
 arch/x86/kernel/setup.c    |  3 +++
 include/linux/bootconfig.h |  7 ++++++
 init/Kconfig               | 33 ++++++++++++++++++++++++++
 init/main.c                | 19 ++++++++++++---
 lib/Makefile               | 16 +++++++++++++
 lib/bootconfig.c           | 58 ++++++++++++++++++++++++++++++++++++++++++++++
 lib/embedded-cmdline.S     | 16 +++++++++++++
 tools/bootconfig/Makefile  |  2 +-
 10 files changed, 156 insertions(+), 4 deletions(-)
---
base-commit: e7e28506af98ce4e1059e5ec59334b335c00a246
change-id: 20260508-bootconfig_using_tools-cfa7aa9d6a5a

Best regards,
--  
Breno Leitao <leitao@debian.org>

[PATCH 1/4] bootconfig: return 0 from xbc_snprint_cmdline() for a leaf root

[Breno Leitao]

Returning -EINVAL when @root has no descendant key nodes is a quirky
result for a renderer: "nothing to render" is not an error. The only
existing caller, xbc_make_cmdline(), papers over it with a `len <= 0`
check, so the misbehavior is harmless today. The new -C user in
tools/bootconfig added by the follow-up patches propagates the error
and turns an empty "kernel {}" subtree into a build failure.

Short-circuit the leaf-root case and return 0 so the rendered length
matches the rendered content.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 lib/bootconfig.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index f445b7703fdd..3a102c9122f7 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -431,6 +431,16 @@ int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root)
 	const char *val, *q;
 	int ret;
 
+	/*
+	 * A leaf @root (e.g. an empty "kernel {}" subtree, or a key whose
+	 * only child is a value node) has no descendant key/value pairs to
+	 * render. The leaf-finding iterator below would otherwise return
+	 * @root itself, which xbc_node_compose_key_after() rejects with
+	 * -EINVAL.
+	 */
+	if (root && xbc_node_is_leaf(root))
+		return 0;
+
 	xbc_node_for_each_key_value(root, knode, val) {
 		ret = xbc_node_compose_key_after(root, knode,
 					xbc_namebuf, XBC_KEYLEN_MAX);

-- 
2.54.0

[PATCH 2/4] bootconfig: render embedded bootconfig as a kernel cmdline at build time

[Breno Leitao]

Add the build-time pipeline that renders the "kernel" subtree of
CONFIG_BOOT_CONFIG_EMBED_FILE into a flat cmdline string and stashes
it in .init.rodata as embedded_kernel_cmdline[]. A follow-up patch
adds the runtime helper that prepends this string to boot_command_line
during early architecture setup so parse_early_param() sees the values.

The build wires up:
  tools/bootconfig -C kernel - userspace tool already shared with
                               lib/bootconfig.c, used here in -C mode
                               to render a bootconfig file to a cmdline
  lib/embedded-cmdline.S     - .incbin's the rendered text plus a NUL
  lib/Makefile rule          - runs tools/bootconfig at build time
  Makefile prepare dep       - ensures tools/bootconfig is built first,
                               same pattern as tools/objtool and
                               tools/bpf/resolve_btfids

Drop the test target from tools/bootconfig/Makefile's default 'all'
recipe so that hooking the binary into the kernel build does not run
test-bootconfig.sh on every prepare. The tests stay available as
'make -C tools/bootconfig test', matching the convention of
tools/objtool and tools/bpf/resolve_btfids whose 'all' targets only
build the binary.

Require BOOT_CONFIG_EMBED_FILE to be non-empty before the new option
can be enabled, otherwise tools/bootconfig -C runs against an empty
file and prints a parse error on every kernel build.

The feature gates on CONFIG_ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG, a
silent symbol arches select once they've wired the prepend call into
setup_arch(). No arch selects it in this patch, so the user-visible
CONFIG_BOOT_CONFIG_EMBED_CMDLINE is not yet enableable; when an arch
later opts in, the runtime behavior is added by the follow-up patches.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 Makefile                  |  5 +++++
 init/Kconfig              | 33 +++++++++++++++++++++++++++++++++
 lib/Makefile              | 16 ++++++++++++++++
 lib/embedded-cmdline.S    | 16 ++++++++++++++++
 tools/bootconfig/Makefile |  2 +-
 5 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index d59f703f9797..3ee259d00a9a 100644
--- a/Makefile
+++ b/Makefile
@@ -1543,6 +1543,11 @@ prepare: tools/bpf/resolve_btfids
 endif
 endif
 
+# lib/Makefile invokes tools/bootconfig to render the embedded bconf to cmdline.
+ifdef CONFIG_BOOT_CONFIG_EMBED_CMDLINE
+prepare: tools/bootconfig
+endif
+
 # The tools build system is not a part of Kbuild and tends to introduce
 # its own unique issues. If you need to integrate a new tool into Kbuild,
 # please consider locating that tool outside the tools/ tree and using the
diff --git a/init/Kconfig b/init/Kconfig
index ca35184532dc..5f491a5ac4b8 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1569,6 +1569,39 @@ config BOOT_CONFIG_EMBED_FILE
 	  This bootconfig will be used if there is no initrd or no other
 	  bootconfig in the initrd.
 
+config ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG
+	bool
+	help
+	  Selected by architectures whose setup_arch() prepends the
+	  build-time-rendered embedded bootconfig cmdline to
+	  boot_command_line before parse_early_param() runs.
+
+config BOOT_CONFIG_EMBED_CMDLINE
+	bool "Render embedded bootconfig as kernel cmdline at build time"
+	depends on BOOT_CONFIG_EMBED
+	depends on BOOT_CONFIG_EMBED_FILE != ""
+	depends on ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG
+	default n
+	help
+	  Render the "kernel" subtree of the embedded bootconfig file into a
+	  flat cmdline string at kernel build time and prepend it to
+	  boot_command_line during early architecture setup. This makes
+	  early_param() handlers (e.g. mem=, earlycon=, loglevel=) see the
+	  values supplied via the embedded bootconfig.
+
+	  The runtime bootconfig parser is unaffected, so tree-structured
+	  consumers such as ftrace boot-time tracing keep working.
+
+	  Note: when an initrd also carries a bootconfig, its "kernel"
+	  subtree is still parsed at runtime, but the embedded "kernel"
+	  keys remain in boot_command_line for parse_early_param() and
+	  end up later than the initrd keys in saved_command_line, so
+	  parse_args() last-wins favors the embedded values. If you need
+	  initrd to override embedded kernel.* keys, leave this option
+	  off.
+
+	  If unsure, say N.
+
 config CMDLINE_LOG_WRAP_IDEAL_LEN
 	int "Length to try to wrap the cmdline when logged at boot"
 	default 1021
diff --git a/lib/Makefile b/lib/Makefile
index 6e72d2c1cce7..9de0ac7732a2 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -273,6 +273,22 @@ filechk_defbconf = cat $(or $(real-prereqs), /dev/null)
 $(obj)/default.bconf: $(CONFIG_BOOT_CONFIG_EMBED_FILE) FORCE
 	$(call filechk,defbconf)
 
+obj-$(CONFIG_BOOT_CONFIG_EMBED_CMDLINE) += embedded-cmdline.o
+$(obj)/embedded-cmdline.o: $(obj)/embedded_cmdline.bin
+
+# Render the bootconfig "kernel" subtree to a flat cmdline string using
+# the userspace tools/bootconfig parser (-C mode). The runtime prepend
+# helper enforces COMMAND_LINE_SIZE at boot, so no build-time size
+# check is performed here (COMMAND_LINE_SIZE is an arch header
+# constant, not a Kconfig value).
+quiet_cmd_render_cmdline = BCONF2C $@
+      cmd_render_cmdline = \
+	$(objtree)/tools/bootconfig/bootconfig -C $< > $@
+
+targets += embedded_cmdline.bin
+$(obj)/embedded_cmdline.bin: $(obj)/default.bconf $(objtree)/tools/bootconfig/bootconfig FORCE
+	$(call if_changed,render_cmdline)
+
 obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
 obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
 
diff --git a/lib/embedded-cmdline.S b/lib/embedded-cmdline.S
new file mode 100644
index 000000000000..7e2e1d81af96
--- /dev/null
+++ b/lib/embedded-cmdline.S
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Embed the build-time-rendered bootconfig "kernel" subtree as a flat
+ * cmdline string. setup_arch() prepends this to boot_command_line on
+ * architectures that select ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG.
+ *
+ * Copyright (c) 2026 Meta Platforms, Inc. and affiliates
+ * Copyright (c) 2026 Breno Leitao <leitao@debian.org>
+ */
+	.section .init.rodata, "aw"
+	.global embedded_kernel_cmdline
+embedded_kernel_cmdline:
+	.incbin "lib/embedded_cmdline.bin"
+	.byte 0
+	.global embedded_kernel_cmdline_end
+embedded_kernel_cmdline_end:
diff --git a/tools/bootconfig/Makefile b/tools/bootconfig/Makefile
index 90eb47c9d8de..4e82fd9553cd 100644
--- a/tools/bootconfig/Makefile
+++ b/tools/bootconfig/Makefile
@@ -15,7 +15,7 @@ override CFLAGS += -Wall -g -I$(CURDIR)/include
 ALL_TARGETS := bootconfig
 ALL_PROGRAMS := $(patsubst %,$(OUTPUT)%,$(ALL_TARGETS))
 
-all: $(ALL_PROGRAMS) test
+all: $(ALL_PROGRAMS)
 
 $(OUTPUT)bootconfig: main.c include/linux/bootconfig.h $(LIBSRC)
 	$(CC) $(filter %.c,$^) $(CFLAGS) $(LDFLAGS) -o $@

-- 
2.54.0

[PATCH 3/4] bootconfig: add xbc_prepend_embedded_cmdline() helper

[Breno Leitao]

Add a helper that prepends the build-time-rendered embedded bootconfig
"kernel" subtree (embedded_kernel_cmdline[] from embedded-cmdline.S) to
a cmdline buffer with a separating space. Architectures call this from
setup_arch() before parse_early_param() so early_param() handlers
(mem=, earlycon=, loglevel=, ...) see values supplied via the embedded
bootconfig.

On overflow the helper logs an error and leaves the cmdline untouched
rather than panicking. Booting without the embedded values is better
than refusing to boot, and the error tells the user why their embedded
keys are missing.

When CONFIG_BOOT_CONFIG_EMBED_CMDLINE=n, the public declaration in
<linux/bootconfig.h> resolves to a no-op stub so callers compile
unchanged.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 include/linux/bootconfig.h |  7 +++++++
 lib/bootconfig.c           | 48 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
index 1c7f3b74ffcf..dcb0c86cbc54 100644
--- a/include/linux/bootconfig.h
+++ b/include/linux/bootconfig.h
@@ -308,4 +308,11 @@ static inline const char *xbc_get_embedded_bootconfig(size_t *size)
 }
 #endif
 
+/* Build-time-rendered bootconfig cmdline prepended in setup_arch() */
+#ifdef CONFIG_BOOT_CONFIG_EMBED_CMDLINE
+void __init xbc_prepend_embedded_cmdline(char *dst, size_t size);
+#else
+static inline void xbc_prepend_embedded_cmdline(char *dst, size_t size) { }
+#endif
+
 #endif
diff --git a/lib/bootconfig.c b/lib/bootconfig.c
index 3a102c9122f7..10c62c8600c8 100644
--- a/lib/bootconfig.c
+++ b/lib/bootconfig.c
@@ -19,6 +19,7 @@
 #include <linux/errno.h>
 #include <linux/cache.h>
 #include <linux/compiler.h>
+#include <linux/printk.h>
 #include <linux/sprintf.h>
 #include <linux/memblock.h>
 #include <linux/string.h>
@@ -34,6 +35,53 @@ const char * __init xbc_get_embedded_bootconfig(size_t *size)
 	return (*size) ? embedded_bootconfig_data : NULL;
 }
 #endif
+
+#ifdef CONFIG_BOOT_CONFIG_EMBED_CMDLINE
+/* embedded_kernel_cmdline is defined in embedded-cmdline.S */
+extern __visible const char embedded_kernel_cmdline[];
+extern __visible const char embedded_kernel_cmdline_end[];
+
+/**
+ * xbc_prepend_embedded_cmdline() - Prepend embedded bootconfig cmdline
+ * @dst: cmdline buffer to prepend into (must already contain a NUL byte)
+ * @size: total capacity of @dst in bytes
+ *
+ * Prepend the build-time-rendered "kernel" subtree of the embedded
+ * bootconfig to @dst. The rendered string already ends with a single
+ * space (the xbc_snprint_cmdline() invariant), which serves as the
+ * separator between the embedded keys and any existing content of @dst.
+ * On overflow, log an error and leave @dst untouched rather than
+ * silently truncating: booting without the embedded values is better
+ * than refusing to boot, and the error message tells the user why
+ * their embedded keys are missing.
+ *
+ * Intended to be called from setup_arch() before parse_early_param() so
+ * that early_param() handlers see the embedded values.
+ */
+void __init xbc_prepend_embedded_cmdline(char *dst, size_t size)
+{
+	size_t embed_len = embedded_kernel_cmdline_end - embedded_kernel_cmdline;
+	size_t dst_len;
+
+	if (!size || embed_len <= 1)	/* trailing NUL only */
+		return;
+	embed_len--;			/* exclude trailing NUL byte */
+
+	dst_len = strnlen(dst, size);
+	if (embed_len + dst_len + 1 > size) {
+		pr_err("embedded bootconfig cmdline (%zu bytes) does not fit in COMMAND_LINE_SIZE with %zu bytes already used; ignoring embedded values\n",
+		       embed_len, dst_len);
+		return;
+	}
+
+	if (dst_len)
+		memmove(dst + embed_len, dst, dst_len + 1);
+	else
+		dst[embed_len] = '\0';
+	memcpy(dst, embedded_kernel_cmdline, embed_len);
+}
+#endif
+
 #endif
 
 /*

-- 
2.54.0

[PATCH 4/4] x86/setup: prepend embedded bootconfig cmdline before parse_early_param

[Breno Leitao]

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.

Select ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG so the user-visible
CONFIG_BOOT_CONFIG_EMBED_CMDLINE option becomes selectable on x86.

With this select in place, setup_boot_config() in init/main.c would
otherwise render the embedded "kernel" subtree a second time via
xbc_make_cmdline("kernel") and prepend it to saved_command_line /
static_command_line through extra_command_line, duplicating every
embedded kernel.* key in /proc/cmdline and causing accumulating
handlers (console=, earlycon=, ...) to register the same value twice.
Track whether the bootconfig data came from the embedded source and
skip the duplicate render in that case.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 arch/x86/Kconfig        |  1 +
 arch/x86/kernel/setup.c |  3 +++
 init/main.c             | 19 ++++++++++++++++---
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f24810015234..f839795692b4 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -126,6 +126,7 @@ 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 46882ce79c3a..592c4c79c974 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>
@@ -924,6 +925,8 @@ void __init setup_arch(char **cmdline_p)
 	builtin_cmdline_added = true;
 #endif
 
+	xbc_prepend_embedded_cmdline(boot_command_line, COMMAND_LINE_SIZE);
+
 	strscpy(command_line, boot_command_line, COMMAND_LINE_SIZE);
 	*cmdline_p = command_line;
 
diff --git a/init/main.c b/init/main.c
index e363232b428b..8264bfa97aa2 100644
--- 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;
+	}
 
 	strscpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
 	err = parse_args("bootconfig", tmp_cmdline, NULL, 0, 0, 0, NULL,
@@ -421,8 +424,18 @@ 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
+		 * BOOT_CONFIG_EMBED_CMDLINE is enabled and this bootconfig
+		 * came from the embedded source, setup_arch() already
+		 * prepended the rendered "kernel" subtree to
+		 * boot_command_line; rendering again here would duplicate
+		 * the keys in saved_command_line / static_command_line and
+		 * cause accumulating handlers (console=, earlycon=, ...) to
+		 * re-register the same value.
+		 */
+		if (!IS_ENABLED(CONFIG_BOOT_CONFIG_EMBED_CMDLINE) || !from_embedded)
+			extra_command_line = xbc_make_cmdline("kernel");
 		/* Also, "init." keys are init arguments */
 		extra_init_args = xbc_make_cmdline("init");
 	}

-- 
2.54.0

Re: [PATCH 0/4] bootconfig: embed kernel.* cmdline at build time

[Masami Hiramatsu]

On Wed, 27 May 2026 09:41:33 -0700
Breno Leitao <leitao@debian.org> wrote:

> The userspace pieces (xbc_snprint_cmdline() in lib/, tools/bootconfig -C)
> already landed; this series wires the rendered cmdline into the kernel.
> 
> Motivation: today the embedded bootconfig is parsed at runtime, after
> parse_early_param() has already run, so early_param() handlers can't
> see embedded values. Folding the kernel.* subtree into the cmdline at
> build time gives a CONFIG_CMDLINE-equivalent for embedded-bootconfig
> users without forcing them to maintain two cmdline sources.
> 
> Behaviorally, the "kernel" subtree is rendered to a flat string at
> build time and stashed in .init.rodata. setup_arch() prepends it to
> boot_command_line before parse_early_param() runs. Overflow is a soft
> error: the helper logs and leaves boot_command_line untouched rather
> than panicking, so an oversized embedded bconf cannot brick a boot.
> 

Thanks Breno, yes, that is what I think about.
Let me check it. And could you also check Sashiko's comments?

https://sashiko.dev/#/patchset/20260527-bootconfig_using_tools-v1-0-b6906a86e7d5%40debian.org

Thanks,

> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
> Breno Leitao (4):
>       bootconfig: return 0 from xbc_snprint_cmdline() for a leaf root
>       bootconfig: render embedded bootconfig as a kernel cmdline at build time
>       bootconfig: add xbc_prepend_embedded_cmdline() helper
>       x86/setup: prepend embedded bootconfig cmdline before parse_early_param
> 
>  Makefile                   |  5 ++++
>  arch/x86/Kconfig           |  1 +
>  arch/x86/kernel/setup.c    |  3 +++
>  include/linux/bootconfig.h |  7 ++++++
>  init/Kconfig               | 33 ++++++++++++++++++++++++++
>  init/main.c                | 19 ++++++++++++---
>  lib/Makefile               | 16 +++++++++++++
>  lib/bootconfig.c           | 58 ++++++++++++++++++++++++++++++++++++++++++++++
>  lib/embedded-cmdline.S     | 16 +++++++++++++
>  tools/bootconfig/Makefile  |  2 +-
>  10 files changed, 156 insertions(+), 4 deletions(-)
> ---
> base-commit: e7e28506af98ce4e1059e5ec59334b335c00a246
> change-id: 20260508-bootconfig_using_tools-cfa7aa9d6a5a
> 
> Best regards,
> --  
> Breno Leitao <leitao@debian.org>
> 


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

Re: [PATCH 0/4] bootconfig: embed kernel.* cmdline at build time

[Breno Leitao]

On Fri, May 29, 2026 at 12:15:19AM +0000, Masami Hiramatsu wrote:
> On Wed, 27 May 2026 09:41:33 -0700
> Breno Leitao <leitao@debian.org> wrote:
> 
> > The userspace pieces (xbc_snprint_cmdline() in lib/, tools/bootconfig -C)
> > already landed; this series wires the rendered cmdline into the kernel.
> > 
> > Motivation: today the embedded bootconfig is parsed at runtime, after
> > parse_early_param() has already run, so early_param() handlers can't
> > see embedded values. Folding the kernel.* subtree into the cmdline at
> > build time gives a CONFIG_CMDLINE-equivalent for embedded-bootconfig
> > users without forcing them to maintain two cmdline sources.
> > 
> > Behaviorally, the "kernel" subtree is rendered to a flat string at
> > build time and stashed in .init.rodata. setup_arch() prepends it to
> > boot_command_line before parse_early_param() runs. Overflow is a soft
> > error: the helper logs and leaves boot_command_line untouched rather
> > than panicking, so an oversized embedded bconf cannot brick a boot.
> > 
> 
> Thanks Breno, yes, that is what I think about.
> Let me check it. And could you also check Sashiko's comments?
> 
> https://sashiko.dev/#/patchset/20260527-bootconfig_using_tools-v1-0-b6906a86e7d5%40debian.org

Ack, I will have a look at them, thanks for confirming the direction is
correct.

--breno