#include <stdint.h>
#if defined(__x86_64__)

#define SYS_EXIT 60
void exit(int8_t status) {
  asm volatile(
    "syscall"
    :
    : "a"(SYS_EXIT), "D"(status)
    :
  );
  for(;;);
}

#define SYS_WRITE 1
intptr_t write(int32_t fd, const void* buf, intptr_t size) {
  intptr_t n_written = 0;
  asm volatile (
      "syscall\n"
      "movq %0, %%rax\n"
      : "=r"(n_written)
      : "a"(SYS_WRITE), "D"(fd), "S"(buf), "d"(size)  // RDI, RSI, RDX are used in x86-64 for write args
      : "rcx", "r11", "memory"
  );
  return n_written;
}

#define SYS_READ 0
intptr_t read(int32_t fd, const void* buf, intptr_t size) {
  intptr_t n_read = 0;
  asm volatile (
      "syscall\n"
      "movq %0, %%rax\n"
      : "=r"(n_read)
      : "a"(SYS_READ), "D"(fd), "S"(buf), "d"(size)  // RDI, RSI, RDX are used in x86-64 for write args
      : "rcx", "r11", "memory"
  );
  return n_read;
}

#define SYS_FORK 57
uint32_t fork() {
  uint64_t rtn;
  asm volatile(
    "syscall\n"         // syscall
    "movq %0, %%rax\n"    // save return value
    : "=r"(rtn)
    : "a"(SYS_FORK)
    :
  );
  return (uint32_t)rtn;
}
#endif /* ifdef __x86_64__ */