build: introduce declarative non-recursive build graph

21 files changed, 634 insertions, 107 deletions

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 76466bd..7ccc03d 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -9,14 +9,7 @@
 #   - Q / KBUILD_VERBOSE        : `make V=1` shows full commands,
 #                                  default V=0 prints a one-line summary
 #   - $(call cmd,<name>)        : echo a quiet summary, then run cmd_<name>
-#   - $(call if_changed,<name>) : currently a thin alias for $(cmd) —
-#                                  no .cmd-file hashing yet (Linux's full
-#                                  if_changed uses fixdep to detect both
-#                                  recipe-text and header changes; LumeOS
-#                                  relies on `-MMD -MP` for headers and
-#                                  on `make clean` for flag changes).
-#   - $(call kbuild-objs,...)   : translate Kbuild-style `obj-y := foo.o`
-#                                  entries into SRCS_C / SRCS_CC.
+#   - $(call if_changed,<name>) : rebuild when inputs or the command change.
 #
 # Naming convention adopted from Linux: each command has both a
 # `quiet_cmd_<name>` (single-line summary) and a `cmd_<name>` (full
@@ -49,11 +42,11 @@ echo-cmd = $(if $($(quiet)cmd_$(1)),echo '  $($(quiet)cmd_$(1))';)
 
 cmd = @$(echo-cmd) $(cmd_$(1))
 
-# if_changed currently degenerates to `cmd` — full Linux semantics
-# require tracking the command-line via per-target .<file>.cmd files
-# and comparing on every rebuild, which needs fixdep.  Until LumeOS
-# grows that infrastructure, `make clean` after editing CFLAGS suffices.
-if_changed = $(cmd)
+# Record a checksum of the exact argv next to each output. FORCE makes Make
+# reconsider the action; run-if-changed executes it only for a changed input or
+# command signature.
+if_changed = @scripts/build/run-if-changed.sh \
+	$(dir $@).$(notdir $@).cmd $@ '$($(quiet)cmd_$(1))' $^ -- $(cmd_$(1))
 
 # --- Standard quiet_cmd_* / cmd_* templates ---------------------------
 #
@@ -61,21 +54,99 @@ if_changed = $(cmd)
 # name via $(call cmd,<name>).  Add new pairs here as new recipe shapes
 # show up (e.g., cmd_lz / cmd_gz / cmd_zstd for compressed Image targets).
 
-   quiet_cmd_cc_o_c   = CC      $<
-         cmd_cc_o_c   = $(CC) $(CFLAGS_LIBC) -c $< -o $@
+   quiet_cmd_cc_o_c   = CC      $(PRIVATE_SOURCE)
+         cmd_cc_o_c   = $(CC) $(CFLAGS_LIBC) $(PRIVATE_INCLUDES) $(PRIVATE_DEFINES) $(PRIVATE_CFLAGS) -c $(PRIVATE_SOURCE) -o $@
 
-   quiet_cmd_cxx_o_cc = CXX     $<
-         cmd_cxx_o_cc = $(CXX) $(CXXFLAGS) -c $< -o $@
+   quiet_cmd_cxx_o_cc = CXX     $(PRIVATE_SOURCE)
+         cmd_cxx_o_cc = $(CXX) $(CXXFLAGS) $(PRIVATE_INCLUDES) $(PRIVATE_DEFINES) $(PRIVATE_CXXFLAGS) -c $(PRIVATE_SOURCE) -o $@
 
-   quiet_cmd_as_o_S   = AS      $<
-         cmd_as_o_S   = $(CC) $(ASFLAGS) -c $< -o $@
+   quiet_cmd_as_o_S   = AS      $(PRIVATE_SOURCE)
+         cmd_as_o_S   = $(CC) $(ASFLAGS) $(PRIVATE_INCLUDES) $(PRIVATE_DEFINES) $(PRIVATE_ASFLAGS) -c $(PRIVATE_SOURCE) -o $@
 
    quiet_cmd_cc_s_c   = CC -S   $<
-         cmd_cc_s_c   = $(CC) $(CFLAGS_LIBC) -S $< -o $@
+         cmd_cc_s_c   = $(CC) $(CFLAGS_LIBC) -S $(PRIVATE_SOURCE) -o $@
+
+   quiet_cmd_gen_asm_offsets = GEN     $@
+         cmd_gen_asm_offsets = scripts/build/generate-asm-offsets.sh $@ \
+                               $(ASM_OFFSETS_S) $(ASM_OFFSETS_SED) $(ASM_OFFSETS_C)
+
+   quiet_cmd_autoconf = GEN     $@
+         cmd_autoconf = scripts/build/generate-autoconf.sh $@ \
+             CONFIG_NR_CPUS $(CONFIG_NR_CPUS) value \
+             CONFIG_HZ $(CONFIG_HZ) value \
+             CONFIG_NR_PRIORITIES $(CONFIG_NR_PRIORITIES) value \
+             CONFIG_DEFAULT_PRIORITY $(CONFIG_DEFAULT_PRIORITY) value \
+             CONFIG_IDLE_PRIORITY $(CONFIG_IDLE_PRIORITY) value \
+             CONFIG_DEFAULT_TIMESLICE $(CONFIG_DEFAULT_TIMESLICE) value \
+             CONFIG_PAGE_SIZE $(CONFIG_PAGE_SIZE) value \
+             CONFIG_MAX_ORDER $(CONFIG_MAX_ORDER) value \
+             CONFIG_KERNEL_STACK_SIZE $(CONFIG_KERNEL_STACK_SIZE) value \
+             CONFIG_KASLR $(CONFIG_KASLR) bool \
+             CONFIG_KASLR_POLICY_ID $(CONFIG_KASLR_POLICY_ID) value \
+             CONFIG_KASLR_LOG_LEVEL $(CONFIG_KASLR_LOG_LEVEL) value \
+             CONFIG_STACK_CANARY $(CONFIG_STACK_CANARY) bool \
+             CONFIG_DEBUG $(CONFIG_DEBUG) bool \
+             CONFIG_DEBUG_LOCKS $(CONFIG_DEBUG_LOCKS) bool \
+             CONFIG_SELFTEST $(CONFIG_SELFTEST) bool \
+             CONFIG_KLOG $(CONFIG_KLOG) bool \
+             CONFIG_KERNEL_COMPRESSED $(CONFIG_KERNEL_COMPRESSED) bool
+
+   quiet_cmd_linker_script = LDS     $@
+         cmd_linker_script = $(CC) -E -P -x c $(INCLUDES) $(PRIVATE_SOURCE) -o $@
+
+   quiet_cmd_initramfs = INITRAMFS $(INITRAMFS_SOURCE)
+         cmd_initramfs = scripts/build/generate-initramfs.sh $(GEN_INIT_CPIO) \
+                         ./scripts/gen_initramfs.sh $@ \
+                         $(CONFIG_INITRAMFS_ROOT_UID) $(CONFIG_INITRAMFS_ROOT_GID) \
+                         $(INITRAMFS_SOURCE)
+
+   quiet_cmd_initramfs_obj = AS      $@ (initramfs)
+         cmd_initramfs_obj = $(CC) $(ASFLAGS) \
+                             -DINITRAMFS_IMAGE='"$(INITRAMFS_CPIO)"' \
+                             -c $(PRIVATE_SOURCE) -o $@
 
    quiet_cmd_objcopy_bin = OBJCOPY $@
          cmd_objcopy_bin = $(OBJCOPY) -O binary $< $@
 
+   quiet_cmd_archive = AR      $@
+         cmd_archive = scripts/build/archive.sh $@ $(AR) $(PRIVATE_ARCHIVE_OBJECTS)
+
+   quiet_cmd_host_tool = HOSTCC  $@
+         cmd_host_tool = $(HOSTCC) $(HOSTCFLAGS) $(PRIVATE_HOST_CFLAGS) \
+                         -o $@ $(PRIVATE_HOST_SOURCE)
+
+   quiet_cmd_host_cc_o_c = HOSTCC  $(PRIVATE_SOURCE)
+         cmd_host_cc_o_c = $(HOSTCC) $(HOSTCFLAGS) -MMD -MP -c $(PRIVATE_SOURCE) -o $@
+
+   quiet_cmd_host_cxx_o_cc = HOSTCXX $(PRIVATE_SOURCE)
+         cmd_host_cxx_o_cc = $(HOSTCXX) $(HOSTCXXFLAGS) -MMD -MP -c $(PRIVATE_SOURCE) -o $@
+
+   quiet_cmd_host_archive = HOSTAR  $@
+         cmd_host_archive = scripts/build/archive.sh $@ $(HOSTAR) $(PRIVATE_ARCHIVE_OBJECTS)
+
+   quiet_cmd_host_link = HOSTLD  $@
+         cmd_host_link = $(HOSTCXX) $(HOSTCXXFLAGS) -o $@ \
+                         $(PRIVATE_HOST_OBJECTS) $(PRIVATE_HOST_LIBS)
+
+   quiet_cmd_toolchain_probe = PROBE   toolchain
+         cmd_toolchain_probe = scripts/build/probe-toolchain.sh $@ \
+             $(CC) $(CXX) $(LD) $(COMPILER_FAMILY) $(TARGET_TRIPLE) \
+             '$(GCC_TOOLCHAIN)' '$(GCC_SYSROOT)'
+
+   quiet_cmd_phys_cc_o_c = PHYSCC  $(PRIVATE_SOURCE)
+         cmd_phys_cc_o_c = $(CC) $(PHYS_CFLAGS) -MMD -MP -c $(PRIVATE_SOURCE) -o $@
+
+   quiet_cmd_phys_cxx_o_cc = PHYSCXX $(PRIVATE_SOURCE)
+         cmd_phys_cxx_o_cc = $(CXX) $(PHYS_CXXFLAGS) -MMD -MP -c $(PRIVATE_SOURCE) -o $@
+
+   quiet_cmd_phys_as_o_S = PHYSAS  $(PRIVATE_SOURCE)
+         cmd_phys_as_o_S = $(CC) $(PHYS_ASFLAGS) -MMD -MP -c $(PRIVATE_SOURCE) -o $@
+
+   quiet_cmd_link_vmlume = LD      $@
+         cmd_link_vmlume = scripts/build/link-kernel.sh $@ $(SIZE) \
+                            $(LD) $(LDFLAGS) -T $(LINKER_SCRIPT) -o $@ \
+                            $(KERNEL_LINK_INPUTS) $(INITRAMFS_OBJ)
+
 # Objcopy with custom flags via per-target OBJCOPYFLAGS variable —
 # used by the .pi.o post-processing rule (--prefix-symbols=__pi_ etc.).
    quiet_cmd_objcopy  = OBJCOPY $@
@@ -83,28 +154,3 @@ if_changed = $(cmd)
 
    quiet_cmd_ld_kernel = LD      $@
          cmd_ld_kernel = $(LD) $(LDFLAGS) -T $(LINKER_SCRIPT) -o $@ $^
-
-# --- kbuild-objs: obj-y -> SRCS_C / SRCS_CC ---------------------------
-#
-# Usage from a subdir Makefile (e.g. arch/riscv/kernel/pi/Makefile):
-#
-#     obj-dir := arch/riscv/kernel/pi
-#     obj-y   := fdt_early.pi.o cmdline_early.pi.o archrandom_early.pi.o
-#     $(eval $(call kbuild-objs,$(obj-dir),$(obj-y:.pi.o=.o)))
-#
-# For each <name>.o entry, looks up <dir>/<name>.cc first, then
-# <dir>/<name>.c, and appends to SRCS_CC / SRCS_C respectively.
-# Pure .pi.o entries should be passed through `:.pi.o=.o` first by the
-# caller so the .pi suffix doesn't confuse the source-file lookup.
-
-define _kbuild-find-src
-$(if $(wildcard $(1)/$(basename $(2)).cc),\
-  $(eval SRCS_CC += $(1)/$(basename $(2)).cc),\
-  $(if $(wildcard $(1)/$(basename $(2)).c),\
-    $(eval SRCS_C += $(1)/$(basename $(2)).c),\
-    $(error kbuild-objs: no $(1)/$(basename $(2)).{c,cc} for obj $(2))))
-endef
-
-define kbuild-objs
-$(foreach _obj,$(2),$(call _kbuild-find-src,$(1),$(_obj)))
-endef
diff --git a/scripts/Kconfig.mk b/scripts/Kconfig.mk
index 2bdc934..3db7a2f 100644
--- a/scripts/Kconfig.mk
+++ b/scripts/Kconfig.mk
@@ -6,15 +6,15 @@
 # This file is the heart of the LumeOS build-time configuration system.
 # It mirrors the role of Linux's Kconfig + auto.conf pipeline:
 #
-#   1.  Developer edits  `.config`  (or copies from arch/$(ARCH)/defconfig)
-#   2.  This file reads `.config`, applies defaults for anything missing,
+#   1.  Developer edits `$(O)/.config` (or runs `make O=... defconfig`)
+#   2.  This file reads that configuration and applies missing defaults,
 #       validates constraints, and exports two things:
 #       a) KCPPFLAGS — a set of -DCONFIG_xxx=value flags for the compiler
 #       b) $(BUILD)/generated/autoconf.h — the same values as C #defines
 #
 # Design Principles (matching Linux conventions):
-#   - Every CONFIG_ symbol has a default defined HERE, so a bare `make`
-#     with no .config still builds a sane kernel.
+#   - Every CONFIG_ symbol has a default defined HERE, so an empty output
+#     directory still builds a sane kernel.
 #   - Boolean options use 'y' / 'n'.  Numeric options are plain integers.
 #   - The generated autoconf.h uses the exact same names so that
 #     `#ifdef CONFIG_DEBUG` works identically in Makefile and C.
@@ -23,7 +23,8 @@
 # ------------------------------------------------------------------
 # §1  Read user configuration (if it exists)
 # ------------------------------------------------------------------
--include .config
+KCONFIG_CONFIG ?= $(BUILD)/.config
+-include $(KCONFIG_CONFIG)
 
 # ------------------------------------------------------------------
 # §2  Provide defaults for every CONFIG_ symbol
@@ -143,42 +144,6 @@ endif
 # ------------------------------------------------------------------
 AUTOCONF_H := $(BUILD)/generated/autoconf.h
 
-define generate-autoconf
-	@mkdir -p $(dir $(AUTOCONF_H))
-	@echo "  GEN     $(AUTOCONF_H)"
-	@echo "/* AUTO-GENERATED — DO NOT EDIT */"            >  $(AUTOCONF_H)
-	@echo "/* Generated by scripts/Kconfig.mk */"          >> $(AUTOCONF_H)
-	@echo "#pragma once"                                    >> $(AUTOCONF_H)
-	@echo ""                                                >> $(AUTOCONF_H)
-	@echo "/* Platform */"                                  >> $(AUTOCONF_H)
-	@echo "#define CONFIG_NR_CPUS          $(CONFIG_NR_CPUS)"           >> $(AUTOCONF_H)
-	@echo ""                                                >> $(AUTOCONF_H)
-	@echo "/* Scheduler */"                                 >> $(AUTOCONF_H)
-	@echo "#define CONFIG_HZ               $(CONFIG_HZ)"               >> $(AUTOCONF_H)
-	@echo "#define CONFIG_NR_PRIORITIES    $(CONFIG_NR_PRIORITIES)"     >> $(AUTOCONF_H)
-	@echo "#define CONFIG_DEFAULT_PRIORITY $(CONFIG_DEFAULT_PRIORITY)"  >> $(AUTOCONF_H)
-	@echo "#define CONFIG_IDLE_PRIORITY    $(CONFIG_IDLE_PRIORITY)"     >> $(AUTOCONF_H)
-	@echo "#define CONFIG_DEFAULT_TIMESLICE $(CONFIG_DEFAULT_TIMESLICE)" >> $(AUTOCONF_H)
-	@echo ""                                                >> $(AUTOCONF_H)
-	@echo "/* Memory Management */"                         >> $(AUTOCONF_H)
-	@echo "#define CONFIG_PAGE_SIZE        $(CONFIG_PAGE_SIZE)"         >> $(AUTOCONF_H)
-	@echo "#define CONFIG_MAX_ORDER        $(CONFIG_MAX_ORDER)"         >> $(AUTOCONF_H)
-	@echo "#define CONFIG_KERNEL_STACK_SIZE $(CONFIG_KERNEL_STACK_SIZE)" >> $(AUTOCONF_H)
-	@echo ""                                                >> $(AUTOCONF_H)
-	@echo "/* Security */"                                  >> $(AUTOCONF_H)
-	$(if $(filter y,$(CONFIG_KASLR)),       @echo "#define CONFIG_KASLR           1"  >> $(AUTOCONF_H))
-	@echo "#define CONFIG_KASLR_POLICY_ID  $(CONFIG_KASLR_POLICY_ID)"  >> $(AUTOCONF_H)
-	@echo "#define CONFIG_KASLR_LOG_LEVEL  $(CONFIG_KASLR_LOG_LEVEL)"  >> $(AUTOCONF_H)
-	$(if $(filter y,$(CONFIG_STACK_CANARY)), @echo "#define CONFIG_STACK_CANARY    1"  >> $(AUTOCONF_H))
-	@echo ""                                                >> $(AUTOCONF_H)
-	@echo "/* Debug */"                                     >> $(AUTOCONF_H)
-	$(if $(filter y,$(CONFIG_DEBUG)),        @echo "#define CONFIG_DEBUG           1"  >> $(AUTOCONF_H))
-	$(if $(filter y,$(CONFIG_DEBUG_LOCKS)),  @echo "#define CONFIG_DEBUG_LOCKS     1"  >> $(AUTOCONF_H))
-	$(if $(filter y,$(CONFIG_SELFTEST)),     @echo "#define CONFIG_SELFTEST        1"  >> $(AUTOCONF_H))
-	$(if $(filter y,$(CONFIG_KLOG)),         @echo "#define CONFIG_KLOG            1"  >> $(AUTOCONF_H))
-	$(if $(filter y,$(CONFIG_KERNEL_COMPRESSED)), @echo "#define CONFIG_KERNEL_COMPRESSED 1"  >> $(AUTOCONF_H))
-endef
-
 # ------------------------------------------------------------------
 # §6  Utility targets
 # ------------------------------------------------------------------
@@ -187,29 +152,31 @@ endef
 .PHONY: defconfig savedefconfig showconfig
 
 defconfig:
-	@echo "  DEFCFG  arch/$(CONFIG_ARCH)/defconfig → .config"
-	@cp arch/$(CONFIG_ARCH)/defconfig .config
+	@echo "  DEFCFG  arch/$(CONFIG_ARCH)/defconfig → $(KCONFIG_CONFIG)"
+	@mkdir -p $(dir $(KCONFIG_CONFIG))
+	@cp arch/$(CONFIG_ARCH)/defconfig $(KCONFIG_CONFIG)
 
 # 'make savedefconfig' — save current effective config
 savedefconfig:
-	@echo "  SAVE    .config"
-	@echo "# LumeOS Kernel Configuration (saved $$(date +%Y-%m-%d))" > .config
-	@echo "CONFIG_ARCH             = $(CONFIG_ARCH)"             >> .config
-	@echo "CONFIG_NR_CPUS          = $(CONFIG_NR_CPUS)"          >> .config
-	@echo "CONFIG_HZ               = $(CONFIG_HZ)"               >> .config
-	@echo "CONFIG_NR_PRIORITIES    = $(CONFIG_NR_PRIORITIES)"     >> .config
-	@echo "CONFIG_PAGE_SIZE        = $(CONFIG_PAGE_SIZE)"         >> .config
-	@echo "CONFIG_MAX_ORDER        = $(CONFIG_MAX_ORDER)"         >> .config
-	@echo "CONFIG_KERNEL_STACK_SIZE = $(CONFIG_KERNEL_STACK_SIZE)" >> .config
-	@echo "CONFIG_KASLR            = $(CONFIG_KASLR)"             >> .config
-	@echo "CONFIG_KASLR_POLICY_ID  = $(CONFIG_KASLR_POLICY_ID)"   >> .config
-	@echo "CONFIG_KASLR_LOG_LEVEL  = $(CONFIG_KASLR_LOG_LEVEL)"   >> .config
-	@echo "CONFIG_STACK_CANARY     = $(CONFIG_STACK_CANARY)"      >> .config
-	@echo "CONFIG_DEBUG            = $(CONFIG_DEBUG)"              >> .config
-	@echo "CONFIG_DEBUG_LOCKS      = $(CONFIG_DEBUG_LOCKS)"        >> .config
-	@echo "CONFIG_SELFTEST         = $(CONFIG_SELFTEST)"           >> .config
-	@echo "CONFIG_KLOG             = $(CONFIG_KLOG)"               >> .config
-	@echo "CONFIG_KERNEL_COMPRESSED = $(CONFIG_KERNEL_COMPRESSED)" >> .config
+	@echo "  SAVE    $(KCONFIG_CONFIG)"
+	@mkdir -p $(dir $(KCONFIG_CONFIG))
+	@echo "# LumeOS Kernel Configuration (saved $$(date +%Y-%m-%d))" > $(KCONFIG_CONFIG)
+	@echo "CONFIG_ARCH             = $(CONFIG_ARCH)"             >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_NR_CPUS          = $(CONFIG_NR_CPUS)"          >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_HZ               = $(CONFIG_HZ)"               >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_NR_PRIORITIES    = $(CONFIG_NR_PRIORITIES)"     >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_PAGE_SIZE        = $(CONFIG_PAGE_SIZE)"         >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_MAX_ORDER        = $(CONFIG_MAX_ORDER)"         >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_KERNEL_STACK_SIZE = $(CONFIG_KERNEL_STACK_SIZE)" >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_KASLR            = $(CONFIG_KASLR)"             >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_KASLR_POLICY_ID  = $(CONFIG_KASLR_POLICY_ID)"   >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_KASLR_LOG_LEVEL  = $(CONFIG_KASLR_LOG_LEVEL)"   >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_STACK_CANARY     = $(CONFIG_STACK_CANARY)"      >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_DEBUG            = $(CONFIG_DEBUG)"              >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_DEBUG_LOCKS      = $(CONFIG_DEBUG_LOCKS)"        >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_SELFTEST         = $(CONFIG_SELFTEST)"           >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_KLOG             = $(CONFIG_KLOG)"               >> $(KCONFIG_CONFIG)
+	@echo "CONFIG_KERNEL_COMPRESSED = $(CONFIG_KERNEL_COMPRESSED)" >> $(KCONFIG_CONFIG)
 
 # 'make showconfig' — print effective configuration
 showconfig:
diff --git a/scripts/build/Build.mk b/scripts/build/Build.mk
new file mode 100644
index 0000000..0a15b38
--- /dev/null
+++ b/scripts/build/Build.mk
@@ -0,0 +1,10 @@
+targets += build/host-library-smoke build/host-test-smoke build/phys-library-smoke
+target.build/host-library-smoke.kind := host-library
+target.build/host-library-smoke.sources := scripts/build/tests/host_library.cc
+
+target.build/host-test-smoke.kind := host-test
+target.build/host-test-smoke.sources := scripts/build/tests/host_test.cc
+target.build/host-test-smoke.private-deps := build/host-library-smoke
+
+target.build/phys-library-smoke.kind := phys-library
+target.build/phys-library-smoke.sources := scripts/build/tests/phys_library.cc
diff --git a/scripts/build/archive.sh b/scripts/build/archive.sh
new file mode 100755
index 0000000..79f0bb9
--- /dev/null
+++ b/scripts/build/archive.sh
@@ -0,0 +1,10 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -eu
+archive=$1
+ar=$2
+shift 2
+rm -f "$archive"
+"$ar" rcs "$archive" "$@"
+
diff --git a/scripts/build/check-kernel-elf.sh b/scripts/build/check-kernel-elf.sh
new file mode 100755
index 0000000..eb92b33
--- /dev/null
+++ b/scripts/build/check-kernel-elf.sh
@@ -0,0 +1,47 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -eu
+elf=$1
+readelf=$2
+nm=$3
+arch=$4
+
+case "$arch" in
+    riscv) expected_machine='RISC-V' ;;
+    aarch64) expected_machine='AArch64' ;;
+    x86_64) expected_machine='Advanced Micro Devices X86-64' ;;
+    *) echo "ELF check: unsupported architecture: $arch" >&2; exit 2 ;;
+esac
+
+machine=$($readelf -h "$elf" | sed -n 's/^[[:space:]]*Machine:[[:space:]]*//p')
+[ "$machine" = "$expected_machine" ] || {
+    echo "ELF check: expected machine '$expected_machine', got '$machine'" >&2
+    exit 1
+}
+
+entry=$($readelf -h "$elf" | sed -n 's/^[[:space:]]*Entry point address:[[:space:]]*//p')
+[ -n "$entry" ] && [ "$entry" != 0x0 ] || {
+    echo "ELF check: kernel has no entry point" >&2
+    exit 1
+}
+
+undefined=$($nm -u "$elf" || true)
+[ -z "$undefined" ] || {
+    echo "ELF check: undefined symbols:" >&2
+    printf '%s\n' "$undefined" >&2
+    exit 1
+}
+
+if $readelf -W -l "$elf" | awk '$1 == "LOAD" && $0 ~ /W/ && $0 ~ /E/ { found=1 } END { exit !found }'; then
+    echo "ELF check: writable and executable LOAD segment" >&2
+    exit 1
+fi
+
+$readelf -S "$elf" | grep -q '[.]rela[.]dyn' || {
+    echo "ELF check: missing relocation section .rela.dyn" >&2
+    exit 1
+}
+
+echo "Kernel ELF OK: $machine, entry $entry"
+
diff --git a/scripts/build/environments/host.mk b/scripts/build/environments/host.mk
new file mode 100644
index 0000000..0911ad3
--- /dev/null
+++ b/scripts/build/environments/host.mk
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+HOSTCC ?= cc
+HOSTCXX ?= c++
+HOSTAR ?= ar
+HOSTCFLAGS ?= -O2 -g -Wall -Wextra
+HOSTCXXFLAGS ?= $(HOSTCFLAGS) -std=c++23
+
diff --git a/scripts/build/environments/kernel.mk b/scripts/build/environments/kernel.mk
new file mode 100644
index 0000000..088cdf0
--- /dev/null
+++ b/scripts/build/environments/kernel.mk
@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+WARNINGS ?= -Wall -Wextra -Wno-unused-parameter
+
+ifeq ($(BUILD_VARIANT),release)
+KERNEL_OPT_FLAGS := -O2 -g0 -DNDEBUG
+else
+KERNEL_OPT_FLAGS := -O2 -g
+endif
+
+CFLAGS := $(WARNINGS) $(KERNEL_OPT_FLAGS) \
+          -ffreestanding -nostdlib \
+          -mcmodel=medany -fPIE -MMD -MP \
+          $(TOOLCHAIN_CFLAGS) $(KCPPFLAGS) $(INCLUDES) \
+          -I$(BUILD)/generated
+
+CFLAGS_LIBC := $(CFLAGS) -std=gnu23 -Iinclude/libc-shim \
+               -Wno-parentheses -Wno-sign-compare
+
+CXXFLAGS := $(CFLAGS) $(TOOLCHAIN_CXXFLAGS) -std=c++23 \
+            -fno-exceptions -fno-rtti -fno-use-cxa-atexit \
+            -fno-threadsafe-statics
+
+# Pre-MMU assembly must never use GOT-indirect addressing.
+ASFLAGS := $(filter-out -fPIE,$(CFLAGS)) -fno-pie
+
+LDFLAGS := -nostdlib -shared -Bsymbolic -z notext -z norelro \
+           --no-dynamic-linker
diff --git a/scripts/build/environments/phys.mk b/scripts/build/environments/phys.mk
new file mode 100644
index 0000000..6a11c12
--- /dev/null
+++ b/scripts/build/environments/phys.mk
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# Early physical-address execution environment. It deliberately has no heap,
+# exceptions, RTTI, thread-safe statics, or PIE/GOT assumptions.
+PHYS_CFLAGS := $(WARNINGS) -Os -g -ffreestanding -nostdlib \
+               -fno-pie -fno-stack-protector $(TOOLCHAIN_CFLAGS) \
+               $(KCPPFLAGS) $(INCLUDES) -I$(BUILD)/generated
+PHYS_CXXFLAGS := $(PHYS_CFLAGS) $(TOOLCHAIN_CXXFLAGS) -std=c++23 \
+                 -fno-exceptions -fno-rtti -fno-use-cxa-atexit \
+                 -fno-threadsafe-statics
+PHYS_ASFLAGS := $(PHYS_CFLAGS)
+
diff --git a/scripts/build/generate-asm-offsets.sh b/scripts/build/generate-asm-offsets.sh
new file mode 100755
index 0000000..4e90f94
--- /dev/null
+++ b/scripts/build/generate-asm-offsets.sh
@@ -0,0 +1,25 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -eu
+output=$1
+assembly=$2
+sed_script=$3
+source=$4
+tmp="$output.tmp.$$"
+{
+    echo '/* AUTO-GENERATED — DO NOT EDIT */'
+    echo "/* Generated from $source */"
+    echo '#ifndef _LUME_GENERATED_ASM_OFFSETS_H'
+    echo '#define _LUME_GENERATED_ASM_OFFSETS_H'
+    echo
+    sed -n -f "$sed_script" "$assembly"
+    echo
+    echo '#endif /* _LUME_GENERATED_ASM_OFFSETS_H */'
+} > "$tmp"
+if [ -e "$output" ] && cmp -s "$tmp" "$output"; then
+    rm -f "$tmp"
+else
+    mv -f "$tmp" "$output"
+fi
+
diff --git a/scripts/build/generate-autoconf.sh b/scripts/build/generate-autoconf.sh
new file mode 100755
index 0000000..493d630
--- /dev/null
+++ b/scripts/build/generate-autoconf.sh
@@ -0,0 +1,29 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -eu
+output=$1
+shift
+tmp="$output.tmp.$$"
+mkdir -p "$(dirname "$output")"
+{
+    echo '/* AUTO-GENERATED — DO NOT EDIT */'
+    echo '#pragma once'
+    while [ "$#" -gt 0 ]; do
+        name=$1
+        value=$2
+        kind=$3
+        shift 3
+        if [ "$kind" = bool ]; then
+            [ "$value" = y ] && echo "#define $name 1"
+        else
+            echo "#define $name $value"
+        fi
+    done
+} > "$tmp"
+if [ -e "$output" ] && cmp -s "$tmp" "$output"; then
+    rm -f "$tmp"
+else
+    mv -f "$tmp" "$output"
+fi
+
diff --git a/scripts/build/generate-initramfs.sh b/scripts/build/generate-initramfs.sh
new file mode 100755
index 0000000..194e206
--- /dev/null
+++ b/scripts/build/generate-initramfs.sh
@@ -0,0 +1,12 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -eu
+generator=$1
+wrapper=$2
+output=$3
+uid=$4
+gid=$5
+source=$6
+GEN_INIT_CPIO=$generator "$wrapper" -o "$output" -u "$uid" -g "$gid" "$source"
+
diff --git a/scripts/build/link-kernel.sh b/scripts/build/link-kernel.sh
new file mode 100755
index 0000000..31164e7
--- /dev/null
+++ b/scripts/build/link-kernel.sh
@@ -0,0 +1,10 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -eu
+output=$1
+size_tool=$2
+shift 2
+"$@"
+"$size_tool" "$output"
+
diff --git a/scripts/build/probe-toolchain.sh b/scripts/build/probe-toolchain.sh
new file mode 100755
index 0000000..2f1f600
--- /dev/null
+++ b/scripts/build/probe-toolchain.sh
@@ -0,0 +1,48 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -eu
+output=$1
+cc=$2
+cxx=$3
+ld=$4
+family=$5
+target=$6
+gcc_toolchain=$7
+sysroot=$8
+
+set --
+if [ "$family" = clang ]; then
+    set -- "$@" "--target=$target"
+    [ -z "$gcc_toolchain" ] || set -- "$@" "--gcc-toolchain=$gcc_toolchain"
+    [ -z "$sysroot" ] || set -- "$@" "--sysroot=$sysroot"
+fi
+
+probe() {
+    language=$1
+    standard=$2
+    shift 2
+    compiler=$cc
+    [ "$language" = c++ ] && compiler=$cxx
+    printf '' | "$compiler" "$@" "-std=$standard" -x "$language" \
+        -fsyntax-only - >/dev/null 2>&1
+}
+
+tmp="$output.tmp.$$"
+mkdir -p "$(dirname "$output")"
+{
+    echo "cc=$($cc --version | head -n 1)"
+    echo "cxx=$($cxx --version | head -n 1)"
+    echo "ld=$($ld --version | head -n 1)"
+    echo "target=$target"
+    printf 'c23='; if probe c gnu23 "$@"; then echo yes; else echo no; fi
+    printf 'cxx23='; if probe c++ c++23 "$@"; then echo yes; else echo no; fi
+    printf 'fno-pie='; if probe c++ c++23 "$@" -fno-pie; then echo yes; else echo no; fi
+    printf 'mcmodel-medany='; if probe c++ c++23 "$@" -mcmodel=medany; then echo yes; else echo no; fi
+} > "$tmp"
+mv -f "$tmp" "$output"
+
+grep -q '^c23=yes$' "$output"
+grep -q '^cxx23=yes$' "$output"
+grep -q '^fno-pie=yes$' "$output"
+grep -q '^mcmodel-medany=yes$' "$output"
diff --git a/scripts/build/run-if-changed.sh b/scripts/build/run-if-changed.sh
new file mode 100755
index 0000000..6cdc7c4
--- /dev/null
+++ b/scripts/build/run-if-changed.sh
@@ -0,0 +1,45 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -eu
+
+cmdfile=$1
+output=$2
+description=$3
+shift 3
+
+rebuild=false
+if [ ! -e "$output" ] || [ ! -e "$cmdfile" ]; then
+    rebuild=true
+fi
+
+while [ "$#" -gt 0 ] && [ "$1" != "--" ]; do
+    prerequisite=$1
+    shift
+    if [ "$prerequisite" != FORCE ] && [ -e "$prerequisite" ] && \
+       [ "$prerequisite" -nt "$output" ]; then
+        rebuild=true
+    fi
+done
+
+[ "$#" -gt 0 ] || { echo "run-if-changed: missing --" >&2; exit 2; }
+shift
+
+signature=$(printf '%s\0' "$@" | cksum)
+old_signature=
+if [ -e "$cmdfile" ]; then
+    old_signature=$(cat "$cmdfile")
+fi
+if [ "$signature" != "$old_signature" ]; then
+    rebuild=true
+fi
+
+if [ "$rebuild" = true ]; then
+    printf '  %s\n' "$description"
+    mkdir -p "$(dirname "$output")" "$(dirname "$cmdfile")"
+    "$@"
+    tmp="$cmdfile.tmp.$$"
+    printf '%s\n' "$signature" > "$tmp"
+    mv -f "$tmp" "$cmdfile"
+fi
+
diff --git a/scripts/build/targets.mk b/scripts/build/targets.mk
new file mode 100644
index 0000000..1a66379
--- /dev/null
+++ b/scripts/build/targets.mk
@@ -0,0 +1,81 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (C) 2026 Richard Qin
+
+# Declarative target registry for the LumeOS build.
+#
+# Build.mk files populate target.<name>.* and append the name to targets.  A
+# target name is metadata, not a Make rule, so names may contain '/' and ':'.
+
+target-kinds := \
+    interface-library header-library object-library source-set \
+    static-library whole-archive host-library phys-library host-tool generated \
+    binary-blob kernel-test host-test product
+targets :=
+generated-actions := autoconf asm-offsets linker-script initramfs
+
+empty :=
+space := $(empty) $(empty)
+comma := ,
+
+# Convert a logical target/source name into a path-safe component.
+target-key = $(subst :,_,$(subst /,_,$(1)))
+
+# Recursively collect a target and all of its dependencies. Dependency cycles
+# are rejected separately before this is evaluated for build roots.
+target-deps = $(sort $(target.$(1).deps) $(target.$(1).public-deps) \
+    $(target.$(1).private-deps) $(target.$(1).interface-deps) \
+    $(target.$(1).link-deps) $(target.$(1).tool-deps) \
+    $(target.$(1).generated-deps) $(target.$(1).runtime-deps) \
+    $(target.$(1).order-only-deps))
+target-closure = $(strip \
+    $(if $(filter $(1),$(2)),$(error target dependency cycle: $(2) -> $(1))) \
+    $(1) $(foreach dep,$(call target-deps,$(1)),$(call target-closure,$(dep),$(2) $(1))))
+target-link-deps = $(sort $(target.$(1).deps) $(target.$(1).public-deps) \
+    $(target.$(1).private-deps) $(target.$(1).interface-deps) \
+    $(target.$(1).link-deps))
+target-link-order = $(strip $(1) $(foreach dep,$(call target-link-deps,$(1)),\
+    $(call target-link-order,$(dep))))
+unique-words = $(if $(strip $(1)),$(firstword $(1)) \
+    $(call unique-words,$(filter-out $(firstword $(1)),$(1))))
+
+duplicate-words = $(sort $(foreach word,$(1),\
+    $(if $(word 2,$(filter $(word),$(1))),$(word))))
+all-target-sources = $(foreach target,$(targets),$(target.$(target).sources))
+duplicate-target-sources = $(call duplicate-words,$(all-target-sources))
+
+define validate-target
+$(if $(filter $(target.$(1).kind),$(target-kinds)),,$(error target '$(1)' has invalid kind '$(target.$(1).kind)'))
+$(if $(filter header-library interface-library product generated binary-blob,$(target.$(1).kind)),$(if $(strip $(target.$(1).sources)),$(error target '$(1)' of kind $(target.$(1).kind) declares sources),),)
+$(if $(filter host-tool,$(target.$(1).kind)),$(if $(word 2,$(target.$(1).sources)),$(error host-tool '$(1)' currently requires exactly one source),),)
+$(foreach src,$(target.$(1).sources),$(if $(wildcard $(src)),,$(error target '$(1)' references missing source '$(src)')))
+$(foreach dep,$(call target-deps,$(1)),$(if $(filter $(dep),$(targets)),,$(error target '$(1)' references unknown dependency '$(dep)')))
+$(foreach dep,$(call target-deps,$(1)),$(if $(strip $(target.$(dep).visibility)),\
+    $(if $(filter all $(1),$(target.$(dep).visibility)),,\
+    $(error target '$(1)' cannot depend on '$(dep)': visibility is '$(target.$(dep).visibility)')),))
+$(if $(filter generated,$(target.$(1).kind)),$(if $(strip $(target.$(1).outputs)),,$(error generated target '$(1)' has no outputs)),)
+$(if $(filter generated,$(target.$(1).kind)),$(if $(filter $(target.$(1).action),$(generated-actions)),,$(error generated target '$(1)' has invalid action '$(target.$(1).action)')),)
+endef
+
+define validate-targets
+$(if $(strip $(targets)),,$(error no build targets were registered))
+$(if $(filter-out $(words $(sort $(targets))),$(words $(targets))),$(error duplicate build target name),)
+$(foreach target,$(targets),$(call validate-target,$(target)))
+endef
+
+# Usage requirements are deliberately separate from link inputs. Public
+# include paths and defines propagate through deps; private values apply only
+# while compiling the target itself.
+target-public-closure = $(sort $(1) $(foreach dep,$(target.$(1).public-deps) \
+    $(target.$(1).deps),$(call target-public-closure,$(dep))))
+target-public-includes = $(sort $(foreach target,$(call target-public-closure,$(1)),$(target.$(target).public-includes)))
+target-public-after-includes = $(sort $(foreach target,$(call target-public-closure,$(1)),$(target.$(target).public-after-includes)))
+target-public-defines = $(sort $(foreach target,$(call target-public-closure,$(1)),$(target.$(target).public-defines)))
+
+target-usage-roots = $(sort $(1) $(target.$(1).deps) $(target.$(1).public-deps) \
+    $(target.$(1).private-deps) $(target.$(1).interface-deps))
+target-compile-includes = $(sort $(target.$(1).private-includes) \
+    $(foreach root,$(call target-usage-roots,$(1)),$(call target-public-includes,$(root))))
+target-compile-after-includes = $(sort $(target.$(1).private-after-includes) \
+    $(foreach root,$(call target-usage-roots,$(1)),$(call target-public-after-includes,$(root))))
+target-compile-defines = $(sort $(target.$(1).private-defines) \
+    $(foreach root,$(call target-usage-roots,$(1)),$(call target-public-defines,$(root))))
diff --git a/scripts/build/tests/host_library.cc b/scripts/build/tests/host_library.cc
new file mode 100644
index 0000000..c545815
--- /dev/null
+++ b/scripts/build/tests/host_library.cc
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+namespace lume::build::test {
+
+int HostLibrarySmokeTestSymbol() { return 0; }
+
+}  // namespace lume::build::test
+
diff --git a/scripts/build/tests/host_test.cc b/scripts/build/tests/host_test.cc
new file mode 100644
index 0000000..6b13417
--- /dev/null
+++ b/scripts/build/tests/host_test.cc
@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+namespace lume::build::test {
+int HostLibrarySmokeTestSymbol();
+}
+
+int main() { return lume::build::test::HostLibrarySmokeTestSymbol(); }
diff --git a/scripts/build/tests/phys_library.cc b/scripts/build/tests/phys_library.cc
new file mode 100644
index 0000000..2cf1596
--- /dev/null
+++ b/scripts/build/tests/phys_library.cc
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+extern "C" unsigned long LumePhysBuildSmoke(unsigned long value) {
+  return value ^ 0x4c554d45UL;
+}
diff --git a/scripts/build/toolchain.mk b/scripts/build/toolchain.mk
new file mode 100644
index 0000000..49d4f0a
--- /dev/null
+++ b/scripts/build/toolchain.mk
@@ -0,0 +1,103 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (C) 2026 Richard Qin
+
+# Toolchain selection:
+#   make                         GCC + GNU ld
+#   make LLVM=1                  Clang + GNU ld
+#   make LLVM=1 LD_TYPE=lld      Clang + LLD
+
+LLVM          ?= 0
+LLVM_VERSION  ?= 20
+LD_TYPE       ?= bfd
+LLVM_BINUTILS ?= 0
+CXX_STDLIB    ?= libstdc++
+CXX_ABI       ?= lume
+COMPILER_RUNTIME ?= compiler-default
+
+GCC_TOOLCHAIN ?=
+CROSS_COMPILE ?=
+
+ifeq ($(ARCH),riscv)
+TARGET_TRIPLE := riscv64-unknown-linux-gnu
+ifeq ($(strip $(GCC_TOOLCHAIN)),)
+ifneq ($(wildcard /opt/riscv64-glibc/bin/riscv64-unknown-linux-gnu-g++),)
+GCC_TOOLCHAIN := /opt/riscv64-glibc
+endif
+endif
+ifeq ($(strip $(CROSS_COMPILE)),)
+ifneq ($(strip $(GCC_TOOLCHAIN)),)
+CROSS_COMPILE := $(GCC_TOOLCHAIN)/bin/$(TARGET_TRIPLE)-
+else
+CROSS_COMPILE := $(TARGET_TRIPLE)-
+endif
+endif
+else ifeq ($(ARCH),aarch64)
+TARGET_TRIPLE := aarch64-linux-gnu
+else ifeq ($(ARCH),x86_64)
+TARGET_TRIPLE := x86_64-linux-gnu
+endif
+
+ifeq ($(strip $(CROSS_COMPILE)),)
+CROSS_COMPILE := $(TARGET_TRIPLE)-
+endif
+ifeq ($(strip $(GCC_TOOLCHAIN)),)
+GCC_TOOLCHAIN := $(patsubst %/bin/,%, $(dir $(CROSS_COMPILE)))
+endif
+
+GCC_SYSROOT := $(strip $(shell $(CROSS_COMPILE)g++ -print-sysroot 2>/dev/null))
+
+CLANG_SUFFIX := $(if $(LLVM_VERSION),-$(LLVM_VERSION),)
+CLANG         ?= clang$(CLANG_SUFFIX)
+CLANGXX       ?= clang++$(CLANG_SUFFIX)
+LLD           ?= ld.lld$(CLANG_SUFFIX)
+
+CLANG_TARGET_FLAGS := --target=$(TARGET_TRIPLE)
+ifneq ($(strip $(GCC_TOOLCHAIN)),)
+CLANG_TARGET_FLAGS += --gcc-toolchain=$(GCC_TOOLCHAIN)
+endif
+ifneq ($(strip $(GCC_SYSROOT)),)
+CLANG_TARGET_FLAGS += --sysroot=$(GCC_SYSROOT)
+endif
+
+ifeq ($(LLVM),1)
+CC  := $(CLANG)
+CXX := $(CLANGXX)
+COMPILER_FAMILY := clang
+TOOLCHAIN_CFLAGS := $(CLANG_TARGET_FLAGS)
+ifeq ($(CXX_STDLIB),libstdc++)
+TOOLCHAIN_CXXFLAGS := -stdlib=libstdc++
+else
+$(error unsupported CXX_STDLIB '$(CXX_STDLIB)' for the current imported runtime)
+endif
+ifeq ($(LD_TYPE),lld)
+LD := $(LLD)
+LINKER_FAMILY := lld
+else
+ifneq ($(CXX_STDLIB),libstdc++)
+$(error GCC configuration currently requires CXX_STDLIB=libstdc++)
+endif
+LD := $(CROSS_COMPILE)ld
+LINKER_FAMILY := bfd
+endif
+else
+CC  := $(CROSS_COMPILE)gcc
+CXX := $(CROSS_COMPILE)g++
+LD  := $(CROSS_COMPILE)ld
+COMPILER_FAMILY := gcc
+LINKER_FAMILY := bfd
+endif
+
+ifeq ($(LLVM_BINUTILS),1)
+AR      := llvm-ar$(CLANG_SUFFIX)
+NM      := llvm-nm$(CLANG_SUFFIX)
+OBJCOPY := llvm-objcopy$(CLANG_SUFFIX)
+OBJDUMP := llvm-objdump$(CLANG_SUFFIX)
+READELF := llvm-readelf$(CLANG_SUFFIX)
+else
+AR      := $(CROSS_COMPILE)ar
+NM      := $(CROSS_COMPILE)nm
+OBJCOPY := $(CROSS_COMPILE)objcopy
+OBJDUMP := $(CROSS_COMPILE)objdump
+READELF := $(CROSS_COMPILE)readelf
+endif
+SIZE := $(CROSS_COMPILE)size
diff --git a/scripts/build/write-compdb.py b/scripts/build/write-compdb.py
new file mode 100755
index 0000000..9ec5a49
--- /dev/null
+++ b/scripts/build/write-compdb.py
@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+import json
+import pathlib
+import sys
+
+source = pathlib.Path(sys.argv[1])
+output = pathlib.Path(sys.argv[2])
+directory = pathlib.Path.cwd()
+entries = []
+for line in source.read_text().splitlines():
+    file_name, object_name, command = line.split("\t", 2)
+    entries.append(
+        {
+            "directory": str(directory),
+            "file": file_name,
+            "output": object_name,
+            "command": command,
+        }
+    )
+output.parent.mkdir(parents=True, exist_ok=True)
+temporary = output.with_suffix(output.suffix + ".tmp")
+temporary.write_text(json.dumps(entries, indent=2) + "\n")
+temporary.replace(output)
+
diff --git a/scripts/gen_initramfs.sh b/scripts/gen_initramfs.sh
index 7eba2fd..8ad0cd7 100755
--- a/scripts/gen_initramfs.sh
+++ b/scripts/gen_initramfs.sh
@@ -247,4 +247,4 @@ done
 
 # If output_file is set we will generate cpio archive
 # we are careful to delete tmp files
-usr/gen_init_cpio $output $timestamp $cpio_list
+"${GEN_INIT_CPIO:-usr/gen_init_cpio}" $output $timestamp $cpio_list