1 files changed, 147 insertions, 0 deletions
diff --git a/src/loader/protocols/mb1.c b/src/loader/protocols/mb1.c
new file mode 100644
index 0000000..cd57fad
--- /dev/null
+++ b/src/loader/protocols/mb1.c
@@ -0,0 +1,147 @@
+// MIT License, Copyright (c) 2021 Marvin Borner
+// Everything according to spec
+
+#include <elf.h>
+#include <library.h>
+#include <memory.h>
+#include <panic.h>
+#include <protocols/mb1.h>
+
+// The address where data gets stored
+#define MB1_LOAD_ADDRESS 0x20000
+
+#define MB1_FLAG_PAGE_ALIGN (1 << 0) // Align modules with page boundaries (4K)
+#define MB1_FLAG_MEMORY_INFO (1 << 1) // Load/store all memory_* fields and mmap_* structs
+#define MB1_FLAG_VIDEO_MODE (1 << 2) // Load/store video mode table
+#define MB1_FLAG_MANUAL_ADDRESSES (1 << 16) // Use specified load addresses
+
+struct mb1_entry {
+	u32 magic;
+	u32 flags;
+	u32 checksum; // Everything after that is optional
+	u32 header_addr; // Unsupported
+	u32 load_addr; // Unsupported
+	u32 load_end_addr; // Unsupported
+	u32 bss_end_addr; // Unsupported
+	u32 entry_addr; // Unsupported
+	u32 mode_type;
+	u32 width;
+	u32 height;
+	u32 depth;
+};
+
+// The (really simple) multiboot checksum algorithm
+static u32 mb1_checksum(struct mb1_entry *entry)
+{
+	return -(entry->magic + entry->flags);
+}
+
+// Load data into memory and return address (not overlapping)
+static u32 mb1_store(void *data, u32 size)
+{
+	static u32 offset = 0;
+	memcpy((void *)(MB1_LOAD_ADDRESS + offset), data, size);
+	offset += size;
+	return MB1_LOAD_ADDRESS + (offset - size);
+}
+
+static void mb1_store_memory_info(struct mb1_info *info)
+{
+	// TODO: Store memory_lower and memory_upper
+	struct memory_map *memory_map = memory_map_get();
+	info->flags |= MB1_INFO_MEMORY_MAP;
+	info->mmap_length = memory_map->count * sizeof(struct mb1_mmap_entry);
+	info->mmap_addr = mb1_store(NULL, 0);
+	for (u32 i = 0; i < memory_map->count; i++) {
+		struct mb1_mmap_entry mmap_entry = { 0 };
+		mmap_entry.struct_size = sizeof(mmap_entry) - 4;
+		mmap_entry.addr_low = memory_map->entry[i].base;
+		mmap_entry.len_low = memory_map->entry[i].length;
+		mmap_entry.type = memory_map->entry[i].type;
+		mb1_store(&mmap_entry, sizeof(mmap_entry));
+	}
+}
+
+// Load the mb1 structs into memory
+static void mb1_load(struct mb1_entry *entry)
+{
+	struct mb1_info info_struct = { 0 };
+	struct mb1_info *info = (void *)mb1_store(&info_struct, sizeof(info_struct));
+
+	// Set boot device
+	info->flags |= MB1_INFO_BOOTDEV;
+	info->boot_device = boot_disk;
+
+	// Set bootloader name
+	info->flags |= MB1_INFO_BOOT_LOADER_NAME;
+	char loader_name[] = "SegelBoot";
+	info->boot_loader_name = mb1_store(loader_name, sizeof(loader_name));
+
+	// Store memory info
+	if (entry->flags & MB1_FLAG_MEMORY_INFO)
+		mb1_store_memory_info(info);
+}
+
+// Jump to kernel with correct info pointer in eax
+static void mb1_jump(u32 entry, u32 info)
+{
+	log("Jumping. So long and thanks for all the fish!\n");
+
+	// Move and jump!
+	__asm__ volatile("movl $" STRINGIFY(MB1_LOAD_MAGIC) ", %%eax\n\t"
+							    "jmpl *%%edi\n\t"
+			 :
+			 : "D"(entry), "b"(info)
+			 : "memory");
+
+	panic("Jumper returned\n");
+}
+
+// Detect and verify mb1
+u8 mb1_detect(struct config_entry *cfg)
+{
+	u8 header[8192] = { 0 };
+
+	s32 ret = cfg->dev->p.disk.fs.read(cfg->path, header, 0, sizeof(header), cfg->dev);
+	if (ret < 12)
+		return 0;
+
+	// Find start of multiboot entry by searching for magic
+	struct mb1_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;
+
+	cfg->impl.type = IMPL_MB1;
+	cfg->impl.offset = (u32)entry - (u32)header;
+
+	return 1;
+}
+
+// Execute mb1 type kernel
+void mb1_exec(struct config_entry *cfg)
+{
+	struct mb1_entry mb1_entry = { 0 };
+	s32 ret = cfg->dev->p.disk.fs.read(cfg->path, &mb1_entry, cfg->impl.offset,
+					   sizeof(mb1_entry), cfg->dev);
+	assert(ret == sizeof(mb1_entry));
+	mb1_load(&mb1_entry);
+
+	u32 entry = elf_load(cfg->dev, cfg->path);
+
+	// This is a kind of hacky parameter stack pushing thing, just disable warning :)
+#pragma GCC diagnostic ignored "-Wpedantic"
+	jmp_kernel((void *)mb1_jump, 2, entry, MB1_LOAD_ADDRESS);
+#pragma GCC diagnostic pop
+}