Modularize the build system

This patch utilizes GNU make facilities to modularize the whole build
system, and it is more convenient for maintenance. No standalone bash
scripts are required.

Author: jserv

Makefile

@@ -1,3 +1,5 @@
+include mk/common.mk
+
 CC ?= gcc
 CFLAGS = -O2
 CFLAGS += -Wall -std=gnu99
@@ -9,16 +11,15 @@ BIN = $(OUT)/kvm-host
 
 all: $(BIN)
 
-# Control the build verbosity
-ifeq ("$(VERBOSE)","1")
-    Q :=
-    VECHO = @true
-else
-    Q := @
-    VECHO = @printf
-endif
-
-OBJS := vm.o serial.o main.o pci.o virtio-pci.o virtq.o virtio-blk.o diskimg.o
+OBJS := \
+	vm.o \
+	serial.o \
+	pci.o \
+	virtio-pci.o \
+	virtq.o \
+	virtio-blk.o \
+	diskimg.o \
+	main.o
 OBJS := $(addprefix $(OUT)/,$(OBJS))
 deps := $(OBJS:%.o=%.o.d)
 
@@ -31,17 +32,12 @@ $(OUT)/%.o: src/%.c
 	$(VECHO) "  CC\t$@\n"
 	$(Q)$(CC) -o $@ $(CFLAGS) -c -MMD -MF $@.d $<
 
-$(OUT)/bzImage:
-	$(Q)scripts/build-linux.sh
-
-$(OUT)/rootfs.cpio:
-	$(Q)scripts/build-rootfs.sh
-
-rootfs: $(OUT)/rootfs.cpio
+# Rules for downloading and building the minimal Linux system
+include mk/external.mk
 
-check: $(BIN) $(OUT)/bzImage $(OUT)/rootfs.cpio
-	$(VECHO) "\nOnce the message 'Kernel panic' appears, press ctrl-c to exit\n"
-	$(Q)sudo $(BIN) -k $(OUT)/bzImage -i $(OUT)/rootfs.cpio
+check: $(BIN) $(LINUX_IMG) $(ROOTFS_IMG)
+	$(VECHO) "\nOnce the message 'Kernel panic' appears, press Ctrl-C to exit\n\n"
+	$(Q)sudo $(BIN) -k $(LINUX_IMG) -i $(ROOTFS_IMG)
 
 clean:
 	$(VECHO) "Cleaning...\n"

mk/common.mk

@@ -0,0 +1,25 @@
+UNAME_S := $(shell uname -s)
+ifeq ($(UNAME_S),Darwin)
+    PRINTF = printf
+else
+    PRINTF = env printf
+endif
+
+# Control the build verbosity
+ifeq ("$(VERBOSE)","1")
+    Q :=
+    VECHO = @true
+    REDIR =
+else
+    Q := @
+    VECHO = @$(PRINTF)
+    REDIR = >/dev/null
+endif
+
+# Test suite
+PASS_COLOR = \e[32;01m
+NO_COLOR = \e[0m
+
+notice = $(PRINTF) "$(PASS_COLOR)$(strip $1)$(NO_COLOR)\n"
+
+PARALLEL = -j $(shell nproc)

mk/external.mk

@@ -0,0 +1,66 @@
+# For each external target, the following must be defined in advance:
+#   _SRC_URL : the hyperlink which points to archive.
+#   _SRC : the file to be read by specific executable.
+#   _SRC_SHA1 : the checksum of the content in _SRC
+
+TOP=$(shell pwd)
+CONF=$(TOP)/configs
+FILE=$(TOP)/target
+
+# Linux kernel
+LINUX_VER = 5.18.8
+LINUX_SRC_URL = https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-${LINUX_VER}.tar.xz
+LINUX_SRC = $(OUT)/linux-${LINUX_VER}
+LINUX_SRC_SHA1 = 8db5e3c3bc63a66fba5cdac53c125252dfbf3b82
+
+# BusyBox
+BUSYBOX_VER=1.35.0
+BUSYBOX_SRC_URL = https://busybox.net/downloads/busybox-${BUSYBOX_VER}.tar.bz2
+BUSYBOX_SRC = $(OUT)/busybox-${BUSYBOX_VER}
+BUSYBOX_SRC_SHA1 = 36a1766206c8148bc06aca4e1f134016d40912d0
+
+define download-n-extract
+$(eval $(T)_SRC_ARCHIVE = $(OUT)/$(shell basename $($(T)_SRC_URL)))
+$($(T)_SRC_ARCHIVE):
+	$(VECHO) "  GET\t$$@\n"
+	$(Q)curl --progress-bar -o $$@ -L -C - "$(strip $($(T)_SRC_URL))"
+	$(Q)echo "$(strip $$($(T)_SRC_SHA1))  $$@" | shasum -c
+$($(T)_SRC): $($(T)_SRC_ARCHIVE)
+	$(VECHO) "Unpacking $$@ ... "
+	$(Q)tar -xf $$< -C ${OUT} && $(call notice, [OK])
+endef
+
+EXTERNAL_SRC = LINUX BUSYBOX
+$(foreach T,$(EXTERNAL_SRC),$(eval $(download-n-extract)))
+
+# Build Linux kernel image
+LINUX_IMG = $(OUT)/bzImage
+$(LINUX_IMG): $(LINUX_SRC)
+	$(VECHO) "Configuring Linux kernel... "
+	$(Q)cp -f ${CONF}/linux.config $</.config
+	$(Q)(cd $< ; make ARCH=x86 oldconfig $(REDIR)) && $(call notice, [OK])
+	$(VECHO) "Building Linux kernel image... "
+	$(Q)(cd $< ; make ARCH=x86 bzImage $(PARALLEL) $(REDIR))
+	$(Q)(cd $< ; cp -f arch/x86/boot/bzImage $(TOP)/$(OUT)) && $(call notice, [OK])
+
+# Build busybox single binary
+BUSYBOX_BIN = $(OUT)/rootfs/bin/busybox
+$(BUSYBOX_BIN): $(BUSYBOX_SRC)
+	$(VECHO) "Configuring BusyBox... "
+	$(Q)mkdir $(OUT)/rootfs || (rm -rf $(OUT)/rootfs ; mkdir -p $(OUT)/rootfs)
+	$(Q)cp -f $(CONF)/busybox.config $</.config
+	$(Q)(cd $< ; $(MAKE) oldconfig $(REDIR)) && $(call notice, [OK])
+	$(VECHO) "Building BusyBox single binary... "
+	$(Q)(cd $< ; $(MAKE) $(PARALLEL) 2>/dev/null $(REDIR))
+	$(Q)(cd $< ; $(MAKE) CONFIG_PREFIX='../rootfs' install $(REDIR)) && $(call notice, [OK])
+
+# Generate root file system
+ROOTFS_IMG = $(OUT)/rootfs.cpio
+$(ROOTFS_IMG): $(BUSYBOX_BIN)
+	$(VECHO) "Generating root file system... "
+	$(Q)(cd $(OUT)/rootfs ; \
+	  mv linuxrc init ; \
+	  mkdir -p etc/init.d ; \
+	  cp -f $(FILE)/rc-startup etc/init.d/rcS ; \
+	  chmod 755 etc/init.d/rcS ; \
+	  find . | cpio -o --format=newc > $(TOP)/$(OUT)/rootfs.cpio 2>/dev/null) && $(call notice, [OK])