From fc9d90470463f165a95becbfbad21795fd9752bd Mon Sep 17 00:00:00 2001 From: Breno Leitao Date: Thu, 2 Jul 2026 21:15:45 +0900 Subject: bootconfig: render embedded bootconfig as a kernel cmdline at build time 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_CMDLINE_FROM_BOOTCONFIG 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. Link: https://lore.kernel.org/all/20260626-bootconfig_using_tools-v7-3-24ab72139c29@debian.org/ Reviewed-by: Nicolas Schier Signed-off-by: Breno Leitao Signed-off-by: Masami Hiramatsu (Google) --- init/Kconfig | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) (limited to 'init') diff --git a/init/Kconfig b/init/Kconfig index 5230d4879b1c..598690ec313a 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1566,6 +1566,42 @@ 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 + CMDLINE_FROM_BOOTCONFIG option per-arch, the same + ARCH_SUPPORTS_* idiom used by ARCH_SUPPORTS_CFI, etc. + +config CMDLINE_FROM_BOOTCONFIG + bool "Render embedded bootconfig as kernel cmdline at build time" + depends on BOOT_CONFIG_EMBED_FILE != "" + depends on ARCH_SUPPORTS_CMDLINE_FROM_BOOTCONFIG + depends on CMDLINE = "" + 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 -- cgit