From: Duje Mihanović <duje.mihanovic@skole.hr>
Date: Tue, 28 Jun 2022 10:39:28 +0000 (+0200)
Subject: Complete build system rehaul
X-Git-Url: http://git.dujemihanovic.xyz/%7B%7B%20%24.Site.BaseURL%20%7D%7Dposts/index.xml?a=commitdiff_plain;h=bdad753bd8125abc67a24b5d8030fa9cfb8706db;p=nameless-os.git

Complete build system rehaul

Inspired by Linux, the top Makefile is more recursive and practically every
directory has its own sub-Makefile which builds or includes only code inside its
directory. This new system works beautifully with -B and parallel jobs, while
the previous one would in either case build the bootloader multiple times (and,
in the case of parallel jobs, cause weird sporadic build errors).
---

diff --git a/Makefile b/Makefile
index 5d8c1eb..993a455 100644
--- a/Makefile
+++ b/Makefile
@@ -1,36 +1,22 @@
 export AS = yasm
-ASFLAGS = -g dwarf2 -f elf
 export CC = i686-elf-gcc
-QEMU = qemu-system-i386 -monitor stdio
-
+export QEMU = qemu-system-i386 -monitor stdio
 export GIT_REV = $(shell git describe --long HEAD)
-
-CFLAGS = -g -fgnu89-inline -Ikernel/include -Ikernel/include/arch/x86 -ffreestanding -DGIT_COMMIT=\"$(GIT_REV)\"
-
-KERNEL_OBJ = kernel/entry.o kernel/arch/x86/halt.o kernel/arch/x86/tty/tty.o kernel/drivers/irq/i8259a.o kernel/arch/x86/irq/idt.o kernel/arch/x86/irq/interrupt.o kernel/arch/x86/irq/stub.o kernel/kernel.o
-
-BOOTLOADER_OBJ = boot/x86/mbr boot/x86/vbr-fat32 boot/x86/stage3/LOADER.BIN boot/x86/stage3/loader.elf
+MAKEFLAGS += -rR
 
 default: kernel/kernel.elf bootloader
-
 all: default boot/x86/disk.img
-
-bootloader: $(BOOTLOADER_OBJ)
-
 run: all
 	$(QEMU) boot/x86/disk.img
-
 debug: all
 	$(QEMU) -s -S boot/x86/disk.img
 
-boot/x86/mbr: boot/x86/mbr.s
-boot/x86/vbr-fat32: boot/x86/vbr-fat32.s boot/x86/fat32/*.s 
-boot/x86/stage3/LOADER.BIN: boot/x86/stage3/*.s boot/x86/stage3/*.c boot/x86/fat32/*.s boot/x86/stage3/stage3.ld
-boot/x86/stage3/loader.elf: boot/x86/stage3/*.s boot/x86/stage3/*.c boot/x86/fat32/*.s boot/x86/stage3/stage3.ld
-$(BOOTLOADER_OBJ):
+kernel/kernel.elf:
+	$(MAKE) -C kernel
+bootloader:
 	$(MAKE) -C boot/x86
 
-boot/x86/disk.img: boot/x86/mbr boot/x86/vbr-fat32 boot/x86/stage3/LOADER.BIN boot/x86/disk.dump kernel/kernel.elf
+boot/x86/disk.img: bootloader boot/x86/disk.dump kernel/kernel.elf
 	truncate -s1G boot/x86/disk.img
 	sfdisk boot/x86/disk.img < boot/x86/disk.dump
 	mkfs.fat -F 32 --offset 2048 boot/x86/disk.img
@@ -39,14 +25,11 @@ boot/x86/disk.img: boot/x86/mbr boot/x86/vbr-fat32 boot/x86/stage3/LOADER.BIN bo
 	mcopy -i boot/x86/disk.img@@1M boot/x86/stage3/LOADER.BIN ::.
 	mcopy -i boot/x86/disk.img@@1M kernel/kernel.elf ::./KERNEL.ELF
 
-kernel/kernel.elf: $(KERNEL_OBJ)
-	$(CC) -ffreestanding -nostdlib -o $@ -T kernel/linker.ld ${KERNEL_OBJ} -lgcc
-	i686-elf-objcopy --only-keep-debug kernel/kernel.elf kernel/kernel.dbg
-	i686-elf-objcopy --add-gnu-debuglink=kernel/kernel.dbg kernel/kernel.elf
-	i686-elf-strip --strip-unneeded kernel/kernel.elf
-
 clean:
-	-rm kernel/kernel.{dbg,elf} ${KERNEL_OBJ}
-	cd boot/x86 && $(MAKE) clean
+	$(MAKE) -C boot/x86 clean
+	$(MAKE) -C kernel clean
 
-.PHONY: default all clean run debug bootloader
+# Even though kernel.elf is a real target, it's considered phony so that the
+# kernel Makefile is always run. We don't check is the kernel binary up-to-date
+# here because we want to be more recursive.
+.PHONY: default all clean run debug bootloader kernel/kernel.elf
diff --git a/boot/x86/Makefile b/boot/x86/Makefile
index e75e8dc..3d12d12 100644
--- a/boot/x86/Makefile
+++ b/boot/x86/Makefile
@@ -1,27 +1,19 @@
-default: mbr vbr-fat32 stage3/LOADER.BIN stage3/loader.elf
+BOOTLOADER_OBJ = mbr vbr-fat32
+ASFLAGS_BASE = -w-zeroing
 
-CFLAGS=-g -ffreestanding -Istage3
-LD=i686-elf-gcc
-LDFLAGS=-T stage3/stage3.ld -ffreestanding -nostdlib -g
+default: $(BOOTLOADER_OBJ) stage3
 
-STAGE3_OBJ=stage3/loader.o stage3/paging.o stage3/elf.o stage3/prekernel.o
-
-mbr: mbr.s
-	$(AS) $(ASFLAGS) -w-zeroing -o $@ $<
+stage3:
+	$(MAKE) -C stage3
 
 vbr-fat32: vbr-fat32.s fat32/*.s
-	$(AS) $(ASFLAGS) -o $@ $<
-
-stage3/loader.elf: $(STAGE3_OBJ)
-	$(CC) $(LDFLAGS) -o $@ $^ -lgcc -Wl,--oformat=elf32-i386
-
-stage3/LOADER.BIN: $(STAGE3_OBJ)
-	$(CC) $(LDFLAGS) -o $@ $^ -lgcc
-
-stage3/loader.o: stage3/loader.s stage3/*.s
-	$(AS) $(ASFLAGS) -f elf -g dwarf2 -DGIT_REVISION=\"$(GIT_REV)\" -o $@ $<
 
 clean:
-	-rm mbr vbr-fat32 stage3/LOADER.BIN stage3/loader.elf $(STAGE3_OBJ) disk.img
+	-rm mbr vbr-fat32 disk.img
+	$(MAKE) -C stage3 clean
+
+# Implicit rules
+%: %.s
+	$(AS) $(ASFLAGS_BASE) -f bin $< -o $@
 
-.PHONY : default clean
+.PHONY : default clean stage3
diff --git a/boot/x86/stage3/Makefile b/boot/x86/stage3/Makefile
new file mode 100644
index 0000000..c9622b2
--- /dev/null
+++ b/boot/x86/stage3/Makefile
@@ -0,0 +1,25 @@
+STAGE3_OBJ = loader.o elf.o paging.o prekernel.o
+
+ASFLAGS_BASE = -f elf -g dwarf2 -DGIT_REVISION=\"$(GIT_REV)\"
+CFLAGS_BASE = -ffreestanding -nostdlib -DGIT_REVISION=\"$(GIT_REV)\" -g
+LDFLAGS_BASE = -ffreestanding -nostdlib -g -lgcc -T stage3.ld
+
+default: LOADER.BIN loader.elf
+
+loader.elf: $(STAGE3_OBJ)
+	$(CC) $(LDFLAGS_BASE) $(LDFLAGS) -Wl,--oformat=elf32-i386 $^ -o $@
+
+LOADER.BIN: $(STAGE3_OBJ)
+	$(CC) $(LDFLAGS_BASE) $(LDFLAGS) $^ -o $@
+
+# Implicit rules
+%.o: %.c
+	$(CC) $(CFLAGS_BASE) $(CFLAGS) -c $< -o $@
+
+%.o: %.s
+	$(AS) $(ASFLAGS_BASE) $(ASFLAGS) $< -o $@
+
+clean:
+	-rm -f $(STAGE3_OBJ) LOADER.BIN loader.elf
+
+.PHONY: default clean
diff --git a/boot/x86/stage3/elf.c b/boot/x86/stage3/elf.c
index d3d215f..8621c39 100644
--- a/boot/x86/stage3/elf.c
+++ b/boot/x86/stage3/elf.c
@@ -1,7 +1,7 @@
 /* Code for parsing ELF binaries (the kernel) */
 
-#include <elf.h>
-#include <paging.h>
+#include "elf.h"
+#include "paging.h"
 #include <stdint.h>
 
 int check_elf_header(struct elf_header *header)
diff --git a/boot/x86/stage3/paging.c b/boot/x86/stage3/paging.c
index 5a0e5f7..14afe85 100644
--- a/boot/x86/stage3/paging.c
+++ b/boot/x86/stage3/paging.c
@@ -1,7 +1,7 @@
 /* Code for enabling paging */
 
 #include <stdint.h>
-#include <paging.h>
+#include "paging.h"
 
 /* Preallocated page tables. */
 static uint32_t page_directory[1024] __attribute__((aligned(4096))) __attribute__((section(".data")));
diff --git a/boot/x86/stage3/prekernel.c b/boot/x86/stage3/prekernel.c
index 280c350..07bd721 100644
--- a/boot/x86/stage3/prekernel.c
+++ b/boot/x86/stage3/prekernel.c
@@ -1,5 +1,5 @@
-#include <elf.h>
-#include <paging.h>
+#include "elf.h"
+#include "paging.h"
 
 /* This bit of code will be run right after the segment registers have been set
  * up for protected mode. */
diff --git a/boot/x86/stage3/stage3.ld b/boot/x86/stage3/stage3.ld
index 1accdc0..e8bb5e7 100644
--- a/boot/x86/stage3/stage3.ld
+++ b/boot/x86/stage3/stage3.ld
@@ -4,7 +4,7 @@ OUTPUT_FORMAT(binary)
 SECTIONS {
 	. = 0x1800;
 	.text : {
-		stage3/loader.o(.text)
+		loader.o(.text)
 		*(.text)
 	}
 	.rodata : { *(.rodata) }
diff --git a/kernel/Makefile b/kernel/Makefile
new file mode 100644
index 0000000..a872ca6
--- /dev/null
+++ b/kernel/Makefile
@@ -0,0 +1,26 @@
+KERNEL_OBJ = kernel.o entry.o
+
+include drivers/Makefile
+include arch/x86/Makefile
+
+ASFLAGS_BASE = -f elf -g dwarf2
+CFLAGS_BASE = -fgnu89-inline -ffreestanding -nostdlib -Iinclude -Iinclude/arch/x86 -g -DGIT_COMMIT=\"$(GIT_REV)\"
+LDFLAGS_BASE = -ffreestanding -nostdlib -lgcc -g
+
+kernel.elf kernel.dbg: $(KERNEL_OBJ)
+	$(CC) $(LDFLAGS_BASE) $(LDFLAGS) -T linker.ld $^ -o $@
+	i686-elf-objcopy --only-keep-debug kernel.elf kernel.dbg
+	i686-elf-objcopy --add-gnu-debuglink=kernel.dbg kernel.elf
+	i686-elf-strip --strip-unneeded kernel.elf
+
+clean:
+	-rm $(KERNEL_OBJ) kernel.elf kernel.dbg
+
+# Implicit rules
+%.o: %.c
+	$(CC) $(CFLAGS_BASE) $(CFLAGS) -c $< -o $@
+
+%.o: %.s
+	$(AS) $(ASFLAGS_BASE) $(ASFLAGS) $< -o $@
+
+.PHONY: clean
diff --git a/kernel/arch/x86/Makefile b/kernel/arch/x86/Makefile
new file mode 100644
index 0000000..52224a3
--- /dev/null
+++ b/kernel/arch/x86/Makefile
@@ -0,0 +1,4 @@
+include arch/x86/irq/Makefile
+include arch/x86/tty/Makefile
+
+KERNEL_OBJ += arch/x86/halt.o
diff --git a/kernel/arch/x86/irq/Makefile b/kernel/arch/x86/irq/Makefile
new file mode 100644
index 0000000..3dc6f82
--- /dev/null
+++ b/kernel/arch/x86/irq/Makefile
@@ -0,0 +1 @@
+KERNEL_OBJ += $(addprefix arch/x86/irq/, idt.o interrupt.o stub.o)
diff --git a/kernel/arch/x86/tty/Makefile b/kernel/arch/x86/tty/Makefile
new file mode 100644
index 0000000..0498223
--- /dev/null
+++ b/kernel/arch/x86/tty/Makefile
@@ -0,0 +1 @@
+KERNEL_OBJ += arch/x86/tty/tty.o
diff --git a/kernel/drivers/Makefile b/kernel/drivers/Makefile
new file mode 100644
index 0000000..76d86aa
--- /dev/null
+++ b/kernel/drivers/Makefile
@@ -0,0 +1 @@
+include drivers/irq/Makefile
diff --git a/kernel/drivers/irq/Makefile b/kernel/drivers/irq/Makefile
new file mode 100644
index 0000000..cd5b834
--- /dev/null
+++ b/kernel/drivers/irq/Makefile
@@ -0,0 +1 @@
+KERNEL_OBJ += drivers/irq/i8259a.o
diff --git a/kernel/linker.ld b/kernel/linker.ld
index a6fb8e4..40870da 100644
--- a/kernel/linker.ld
+++ b/kernel/linker.ld
@@ -7,7 +7,7 @@ SECTIONS
 
 	.text : AT(ADDR(.text) - 0xbff00000) ALIGN(4K) {
 		__TEXT_BASE__ = .;
-		kernel/entry.o (.text)
+		entry.o (.text)
 		*(.text)
 		__TEXT_END__ = .;
 	}