write a string to standard output using syscall(2)

test.c

/* save as test.c, compile with gcc test.c -o test -m64 */
#define _GNU_SOURCE        /* See feature_test_macros(7) */
#include <unistd.h>
#include <sys/syscall.h>   /* For SYS_xxx definitions */

void main() {
  const char *buf="test\n";
  syscall(1,   /* sys_write */
          1,   /* stdout    */
          buf, /* buf, or string to write to stdout */
          5    /* num of chars in buf */
         );
}