GCC ARM problem example

activate.s

.global activate
activate:
	b test

bootstrap.s

.global _start
_start:
	ldr sp, =0x07FFFFFF
	bl main

kernel.c

void activate(void);

void test(void) {
	char *s = "Yay!\n";

	while(*s) {
		*(volatile char*)0x101f1000 = *s;
		s++;
	}
}

int main(void) {
	char *string = "Hello, World!\n";
	char *string2 = "Done!\n";

	while(*string) {
		*(volatile char*)0x101f1000 = *string;
		string++;
	}

	activate();

	while(*string2) {
		*(volatile char*)0x101f1000 = *string2;
		string2++;
	}

	while(1); /* We can't exit, there's nowhere to go */
	return 0;
}

Makefile

CC=arm-linux-gnueabi-gcc
LD=arm-linux-gnueabi-ld

CFLAGS=-ansi -pedantic -Wall -Wextra -march=armv6 -msoft-float -fPIC -mapcs-frame
LDFLAGS=-N -Ttext=0x10000

kernel.elf: bootstrap.o kernel.o activate.o

.PHONY: clean

clean:
	$(RM) *.elf *.o

.SUFFIXES: .s .o .elf

.s.o:
	$(CC) $(CFLAGS) -o $@ -c $^

.o.elf:
	$(LD) $(LDFLAGS) -o $@ $^