main.c

#include "syscalls.h"
#define internal static
#define stdout 1
typedef unsigned long int uintptr;  /* size_t */
typedef long int intptr;  /* ssize_t */
#ifdef __x86_64__
asm (
  "_start:\n"
  "    xorl %ebp,%ebp\n"
  "    movq 0(%rsp),%rdi\n"  /* argc loaded */
  "    lea 8(%rsp),%rsi\n"  /* argv[0] loaded */
  "    call main\n"
  "    movq %rax,%rdi\n"
  "    movl $(SYS_exit),%eax\n"
  "    syscall\n"
  "    ret\n");

asm(
  "syscall3:\n"
  "    mov %rdi,%rax\n"
  "    mov %rsi,%rdi\n"
  "    mov %rdx,%rsi\n"
  "    mov %rcx,%rdx\n"
  "    syscall\n"
  "    ret\n"
   );
#endif

uintptr syscall3 (uintptr number, void *arg1, void *arg2, void *arg3);

internal uintptr
write (uintptr fd, const void *data, uintptr n_bytes)
{
  return (uintptr) syscall3 (SYS_write, (void *) fd, (void *) data,
           (void *) n_bytes);
}

internal uintptr
strlen (const char *str)
{
  const char *p;
  for (p = str; *p; ++p);
  return (uintptr) (p - str);
}

internal uintptr
puts (const char *str)
{
  return write (stdout, str, strlen (str));
}

int
main (void)
{
  puts ("hello world\n");
  return 0;
}