push

print.c

@@ -0,0 +1,121 @@
+static long sys_write(int fd, const char *buf, long len)
+{
+    long ret;
+    __asm__ volatile (
+        "syscall"
+        : "=a"(ret)
+        : "0"(1L),
+          "D"((long)fd),
+          "S"(buf),
+          "d"(len)
+        : "rcx", "r11", "memory"
+    );
+    return ret;
+}
+
+static void sys_exit(int code)
+{
+    __asm__ volatile (
+        "syscall"
+        :
+        : "a"(60L),
+          "D"((long)code)
+        :
+    );
+    __builtin_unreachable();
+}
+
+static long strlen(const char *s)
+{
+    long n = 0;
+    while (s[n]) n++;
+    return n;
+}
+
+static void print_char(char c)
+{
+    sys_write(1, &c, 1);
+}
+
+static void str(const char *s)
+{
+    long n = strlen(s);
+    if (n > 0) sys_write(1, s, n);
+}
+
+static void uint(unsigned long v)
+{
+    char buf[20];
+    int  i = 19;
+    buf[i] = '\0';
+    if (v == 0) { print_char('0'); return; }
+    while (v && i > 0) {
+        buf[--i] = '0' + (v % 10);
+        v /= 10;
+    }
+    str(buf + i);
+}
+
+static void print_int(long v)
+{
+    if (v < 0) { print_char('-'); uint((unsigned long)-v); }
+    else         uint((unsigned long)v);
+}
+
+static void hex(unsigned long v)
+{
+    static const char *digits = "0123456789abcdef";
+    char buf[17];
+    int  i = 16;
+    buf[i] = '\0';
+    if (v == 0) { str("0x0"); return; }
+    while (v && i > 0) {
+        buf[--i] = digits[v & 0xf];
+        v >>= 4;
+    }
+    buf[--i] = 'x';
+    buf[--i] = '0';
+    str(buf + i);
+}
+
+typedef __builtin_va_list va_list;
+#define va_start(ap, last) __builtin_va_start(ap, last)
+#define va_arg(ap, T)      __builtin_va_arg(ap, T)
+#define va_end(ap)         __builtin_va_end(ap)
+
+static void impl(const char *fmt, ...)
+{
+    va_list ap;
+    va_start(ap, fmt);
+    for (const char *p = fmt; *p; p++) {
+        if (*p != '%') { print_char(*p); continue; }
+        p++;
+        switch (*p) {
+            case 'd': print_int(va_arg(ap, int));                 break;
+            case 'l': p++;  /* assume %ld */
+                      print_int(va_arg(ap, long));                break;
+            case 'u': uint(va_arg(ap, unsigned int));             break;
+            case 'x': hex(va_arg(ap, unsigned long));             break;
+            case 's': str(va_arg(ap, const char *));              break;
+            case 'c': print_char((char)va_arg(ap, int));          break;
+            case '%': print_char('%');                             break;
+            default:  print_char('%'); print_char(*p);            break;
+        }
+    }
+    va_end(ap);
+}
+
+#define print(fmt, ...) impl((fmt), ##__VA_ARGS__)
+
+void _start(void)
+{
+    print("Hello, world!\n");
+    print("Integer:  %d\n",  -42);
+    print("Unsigned: %u\n",  1337u);
+    print("Hex:      %x\n",  (unsigned long)0xDEADBEEF);
+    print("String:   %s\n",  "no libc needed");
+    print("Char:     %c\n",  'Z');
+    print("Long:     %ld\n", (long)-9876543210L);
+    print("Two args: %d + %d = %d\n", 10, 20, 30);
+    sys_exit(0);
+}