1 files changed, 53 insertions, 2 deletions
diff --git a/src/loader/impl/mb1.c b/src/loader/impl/mb1.c
index 5265082..cb75976 100644
--- a/src/loader/impl/mb1.c
+++ b/src/loader/impl/mb1.c
@@ -1,9 +1,60 @@
 // MIT License, Copyright (c) 2021 Marvin Borner
+// Everything according to spec
 
 #include <impl/mb1.h>
+#include <pnc.h>
 
-u8 mb1_probe(struct dev *dev)
+#define MB1_MAGIC 0x1badb002
+
+struct multiboot_entry {
+	u32 magic;
+	u32 flags;
+	u32 checksum; // Everything after that is optional
+	u32 header_addr;
+	u32 load_addr;
+	u32 load_end_addr;
+	u32 bss_end_addr;
+	u32 entry_addr;
+	u32 mode_type;
+	u32 width;
+	u32 height;
+	u32 depth;
+};
+
+// The (really simple) multiboot checksum algorithm
+static u32 mb1_checksum(struct multiboot_entry *entry)
+{
+	return -(entry->magic + entry->flags);
+}
+
+// Detect and verify mb1
+u8 mb1_detect(struct dev *dev, const char *path)
 {
-	(void)dev;
+	u8 header[8192] = { 0 };
+
+	s32 ret = dev->p.disk.fs.read(path, header, 0, sizeof(header), dev);
+	if (ret < 12)
+		return 0;
+
+	// Find start of multiboot entry by searching for magic
+	struct multiboot_entry *entry = 0;
+	for (u32 i = 0; i < sizeof(header); i++) {
+		u32 *p = (u32 *)&header[i];
+		if (*p == MB1_MAGIC) {
+			entry = (void *)p;
+			break;
+		}
+	}
+
+	if (!entry)
+		return 0;
+
+	u32 checksum = mb1_checksum(entry);
+	if (checksum != entry->checksum)
+		return 0;
+
+	dev->p.disk.impl.type = IMPL_MB1;
+	dev->p.disk.impl.start = entry;
+
 	return 1;
 }