simple macos process with no dependency on libsystem.dylib

macos-syscall.c

/*
 * cc -Wall -O3 -c macos-syscall.c -o macos-syscall.o
 * ld -static -macosx_version_min 10.12 -pagezero_size 0x1000 macos-syscall.o -o macos-syscall
 */

__attribute__ ((visibility("default"))) extern void start(void) asm("start");

#define NR_exit 0x2000001
#define NR_write 0x2000004

static __inline long __syscall0(long n)
{
        unsigned long ret;
        __asm__ __volatile__ ("syscall"
		: "=a"(ret)
		: "a"(n)
		: "rcx", "r11", "memory");
        return ret;
}

static __inline long __syscall3(long n, long a1, long a2, long a3)
{
        unsigned long ret;
        __asm__ __volatile__ ("syscall"
		: "=a"(ret)
		: "a"(n), "D"(a1), "S"(a2), "d"(a3)
		: "rcx", "r11", "memory");
        return ret;
}

void exit(int status)
{
	__syscall0(NR_exit);
	__builtin_unreachable();
}

long write(int fildes, const void *buf, unsigned long nbyte)
{
	return __syscall3(NR_write, fildes, (long)buf, nbyte);
}

void start()
{
	write(1, "hello world\n", 12);
	exit(0);
}