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

@@ -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

@@ -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

@@ -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
 

@@ -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:

@@ -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 $@