On Wed, Jun 17, 2026 at 04:23:35AM -0700, Breno Leitao wrote:
> 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
> (listed under the EXTRA BOOT CONFIG
> MAINTAINERS entry)
> 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.
>
> tools/bootconfig also installs on target systems, so its own Makefile
> keeps $(CC) and stays cross-buildable as a standalone tool. The kernel
> build, which runs the tool on the build host during prepare, instead
> forces CC=$(HOSTCC) from a dedicated tools/bootconfig rule and clears
> CROSS_COMPILE= in the sub-make. Without that clear, an LLVM=1 cross
> build would inherit CROSS_COMPILE and tools/scripts/Makefile.include
> would inject --target=/--sysroot= flags into the host clang invocation,
> producing a target binary that fails to exec ("Exec format error").
>
> embedded-cmdline.S places the rendered string in its own .init.rodata
> subsection (.init.rodata.embed_cmdline) with the "a" (allocatable,
> read-only) flag and %progbits. lib/bootconfig-data.S already places
> the embedded bootconfig blob in .init.rodata with the "aw" flag
> (xbc_init() rewrites separators in place, so that data must be
> writable). Using a distinct subsection name avoids the ld.lld section-
> type mismatch that would otherwise arise from mixing "a" and "aw"
> under the same name; the linker's "*(.init.rodata .init.rodata.*)"
> glob still folds both into the init image and frees them after boot.
>
> A follow-up patch wires the build-time tools/bootconfig into the
> top-level clean target.
>
> Signed-off-by: Breno Leitao <[email protected]>
> ---
> MAINTAINERS | 1 +
> Makefile | 15 +++++++++++++++
> init/Kconfig | 35 +++++++++++++++++++++++++++++++++++
> lib/Makefile | 16 ++++++++++++++++
> lib/embedded-cmdline.S | 16 ++++++++++++++++
> tools/bootconfig/Makefile | 2 +-
> 6 files changed, 84 insertions(+), 1 deletion(-)
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 57656ec0e9d5d..953231df1911d 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -9844,6 +9844,7 @@ F: fs/proc/bootconfig.c
> F: include/linux/bootconfig.h
> F: lib/bootconfig-data.S
> F: lib/bootconfig.c
> +F: lib/embedded-cmdline.S
> F: tools/bootconfig/*
> F: tools/bootconfig/scripts/*
>
> diff --git a/Makefile b/Makefile
> index bf196c6df5b92..a7abb3f9a6264 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1545,6 +1545,21 @@ prepare: tools/bpf/resolve_btfids
> endif
> endif
>
> +# tools/bootconfig renders the embedded bootconfig into a cmdline at build
> time.
> +ifdef CONFIG_BOOT_CONFIG_EMBED_CMDLINE
> +prepare: tools/bootconfig
> +endif
> +
> +# tools/bootconfig is run on the build host during prepare, so force a host
> +# binary here; its own Makefile keeps $(CC) for standalone and cross builds.
> +# CROSS_COMPILE= is cleared so tools/scripts/Makefile.include does not inject
> +# the target's --target=/--sysroot= flags into the host clang invocation
> under
> +# LLVM=1 cross builds (which would produce a target binary that fails to
> exec).
> +tools/bootconfig: FORCE
> + $(Q)mkdir -p $(objtree)/tools
> + $(Q)$(MAKE) O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ \
> + bootconfig CC=$(HOSTCC) CROSS_COMPILE=
sashiko whines (priority: low) about the 'CC=$(HOSTCC)' as HOSTCC might
contains spaces (e.g. "ccache gcc") [1]. Instead of adding quotes (as
sashiko suggests), the CC could be redefined locally for the target, for
example:
tools/bootconfig: export CC := $(HOSTCC)
tools/bootconfig: FORCE
$(Q)mkdir -p $(objtree)/tools
$(Q)$(MAKE) O=$(abspath $(objtree)) subdir=tools -C $(srctree)/tools/ \
bootconfig CROSS_COMPILE=
That way, make handles the variable definition as it should and there is
no interference with shell escaping.
for Kbuild:
Reviewed-by: Nicolas Schier <[email protected]>
Kind regards,
Nicolas
[1]: http://sashiko.dev/#/message/20260617113701.0405E1F000E9%40smtp.kernel.org
> +
> # 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 5230d4879b1c8..d2b8613a6b927 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1566,6 +1566,41 @@ 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
> + Silent symbol; no C code reads it directly. Architectures
> + select it once their setup_arch() calls
> + xbc_prepend_embedded_cmdline() before parse_early_param().
> + Its only role is to gate the user-visible
> + BOOT_CONFIG_EMBED_CMDLINE option per-arch, the same
> + ARCH_SUPPORTS_* idiom used by ARCH_SUPPORTS_CFI, etc.
> +
> +config BOOT_CONFIG_EMBED_CMDLINE
> + bool "Render embedded bootconfig as kernel cmdline at build time"
> + 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 7f75cc6edf94a..4ace86a5cb6de 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-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o
>
> diff --git a/lib/embedded-cmdline.S b/lib/embedded-cmdline.S
> new file mode 100644
> index 0000000000000..bda81b4a42bea
> --- /dev/null
> +++ b/lib/embedded-cmdline.S
> @@ -0,0 +1,16 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Embed the build-time-rendered bootconfig "kernel" subtree as a flat
> + * cmdline string. setup_arch() prepends this to boot_command_line on
> + * architectures that select ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG.
> + *
> + * Copyright (c) 2026 Meta Platforms, Inc. and affiliates
> + * Copyright (c) 2026 Breno Leitao <[email protected]>
> + */
> + .section .init.rodata.embed_cmdline, "a", %progbits
> + .global embedded_kernel_cmdline
> +embedded_kernel_cmdline:
> + .incbin "lib/embedded_cmdline.bin"
> + .byte 0
> + .global embedded_kernel_cmdline_end
> +embedded_kernel_cmdline_end:
> diff --git a/tools/bootconfig/Makefile b/tools/bootconfig/Makefile
> index 90eb47c9d8de6..4e82fd9553cde 100644
> --- a/tools/bootconfig/Makefile
> +++ b/tools/bootconfig/Makefile
> @@ -15,7 +15,7 @@ override CFLAGS += -Wall -g -I$(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 $@
>
> --
> 2.53.0-Meta
>
