Conditional kernel inclusion

Makefile

@@ -4,18 +4,27 @@ TARGET=$(ARCH)-unknown-none
 export LD=ld
 export OBJCOPY=objcopy
 export RUST_TARGET_PATH=$(CURDIR)/targets
-export XARGO_HOME=$(CURDIR)/build/xargo
+export XARGO_HOME=$(CURDIR)/target/xargo
 
 all: build/bootloader
 
-build/libstartup.o: src/nasm/startup.asm src/nasm/* build/kernel
+clean:
+	rm -rf build
+
+build/libstartup.o: src/nasm/startup.asm src/nasm/*
+	mkdir -p build
+ifeq ($(KERNEL),)
 	nasm -f elf32 $< -I src/nasm/ -o $@
+else
+	nasm -f elf32 $< -I src/nasm/ -D KERNEL=$(KERNEL) -o $@
+endif
 
 build/libbootloader.a: Cargo.lock Cargo.toml src/* src/*/* src/*/*/* src/*/*/*/*
 	mkdir -p build
 	xargo rustc --lib --target $(TARGET) --release -- -C soft-float -C debuginfo=2 --emit link=$@
 
 build/bootloader: linkers/$(ARCH).ld build/libstartup.o build/libbootloader.a
+	mkdir -p build
 	$(LD) -m elf_i386 --gc-sections -z max-page-size=0x1000 -T $< -o $@ build/libstartup.o build/libbootloader.a && \
 	$(OBJCOPY) --only-keep-debug $@ $@.sym && \
 	$(OBJCOPY) --strip-debug $@

src/nasm/startup.asm

@@ -43,6 +43,7 @@ long_mode:
     mov gs, rax
     mov ss, rax
 
+%ifdef KERNEL
     ; set kernel size
     mov rax, __kernel_end
     sub rax, __kernel
@@ -61,6 +62,8 @@ long_mode:
     ; entry point
     mov rax, [args.kernel_base]
     call [rax + 0x18]
+%endif
+
 .halt:
     cli
     hlt
@@ -111,6 +114,9 @@ iend
 .end equ $ - gdt
 
 SECTION .kernel
+%ifdef KERNEL
 __kernel:
-INCBIN "build/kernel"
+      %defstr KERNEL_STR %[KERNEL]
+      INCBIN KERNEL_STR
 __kernel_end:
+%endif