uch - messaging program written in assembly

makefile

CC=gcc
LD=ld

CFLAGS=-Wall -Wextra -pedantic -std=c11 -g
LDFLAGS=-entry run

uch: uch.o
	$(LD) $(LDFLAGS) $< -o $@

uch.o: uch.c
	$(CC) $(CFLAGS) -c $< -o $@

clean:
	rm -f uch uch.o

uch.c

#include <x86_64-linux-gnu/asm/unistd.h>

#include <stdint.h>

static _Noreturn void __exit(const uint64_t exitCode);

void run() {

  __exit(0);
}

static _Noreturn void __exit(const uint64_t exitCode) {
  __asm__ ("mov %[n], %%rax;"
	   "mov %[c], %%rdi;"
	   "syscall;"
	   : /* no output */
	   : [n] "i" (__NR_exit), [c] "r" (exitCode)
	   : "rcx", "r11" );
}