Compile and link a bootloader using SDCC

crtstart.asm

	.globl __start__stack
;--------------------------------------------------------
; Stack segment in internal ram
;--------------------------------------------------------
	.area	SSEG	(DATA)
__start__stack:
	.ds	1

 	.area VECTOR    (CODE)
	.globl __interrupt_vect
__interrupt_vect:
 	ljmp	__sdcc_gsinit_startup

	.globl __start__stack

	.area GSINIT0 (CODE)

__sdcc_gsinit_startup::
        mov     sp,#__start__stack - 1

	.area GSFINAL (CODE)
        ljmp	_bootloader

Makefile

ASM= asx8051
CC= sdcc

BOOTLOADER_ADDRESS=0x3000
OUTPUT_DIR= build

.PHONY: $(OUTPUT_DIR)
.SUFFIXES:
.SUFFIXES: .asm .c .ihx .hex .rel

AFLAGS= -plosgff
INCLUDE_DIRS= -I$(TOP)

VPATH=$(TOP)

# !!! main.c must be the first file, otherwise SDCC produces bad output
SRCS= main.c
OBJS= ${SRCS:.c=.rel}

all: $(OUTPUT_DIR)
	@TOP='..' $(MAKE) -e --no-print-directory -C $< --file=../Makefile main.hex

clean:
	rm -rf ${OUTPUT_DIR} *.d52 *.lst *.map *.mem *.rel *.rst *.sym

$(OUTPUT_DIR):
	@mkdir -p ${OUTPUT_DIR}

.asm.rel:
	${ASM} ${AFLAGS} $^
	mv -f $(addprefix $(basename $^), .lst .rel .sym) .

.ihx.hex:
	packihx $< > $@

.c.rel:
	${CC} -c ${CFLAGS} ${INCLUDE_DIRS} $^

main.ihx: $(OBJS) crtstart.rel
	${CC} ${CFLAGS} -Wl-bHOME=${BOOTLOADER_ADDRESS} -o $@ $^