bootconfig: render embedded bootconfig as a kernel cmdline at build time

2026-07-02T12:15:45+00:00

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)

kernel/git/next/linux-next.git/lib/embedded-cmdline.S, branch master

bootconfig: render embedded bootconfig as a kernel cmdline at build time