Add a fat12-enabled boot sector

fat12boot.c

@@ -0,0 +1,59 @@
+#include <stdint.h>
+#include <stdlib.h>
+
+#include "fat12.h"
+
+#define kPolmonAddress ((void*)0x0600)
+#define kFatAddress ((void*)0x1000)
+#define kRootDirAddress ((void*)0x1200)
+
+
+static int putchar(int c) {
+    register uint8_t khar asm ("al") = c;
+    register uint8_t func asm ("ah") = 0x0e;
+    register uint8_t page asm ("bh") = 0;
+
+    asm volatile ("int $0x10"
+            :: "r" (khar), "r" (func), "r" (page)
+            : "bp");
+
+    return c;
+}
+
+static int puts(const char* msg) {
+    while (*msg) {
+        putchar(*msg++);
+    }
+    return 0;
+}
+
+__attribute__((noreturn))
+static void die(const char* msg) {
+    puts(msg);
+    while (1) {
+    }
+    __builtin_unreachable();
+}
+
+__attribute__((noreturn))
+static void jump(void* addr) {
+    asm volatile ("ljmp $0,%0" :: "i"(addr));
+    __builtin_unreachable();
+}
+
+__attribute__((noreturn))
+static void loadpolmon() {
+    if (fat12_init(kFatAddress, kRootDirAddress)) {
+        die("fi");
+    }
+
+    if (fat12_readfile("POLMON  COM", kPolmonAddress)) {
+        die("pnf");
+    }
+
+    jump(kPolmonAddress);
+}
+
+int main() {
+    loadpolmon();
+}