1 files changed, 72 insertions, 0 deletions
diff --git a/boot.cpp b/boot.cpp
new file mode 100644
index 0000000..0b003fd
--- /dev/null
+++ b/boot.cpp
@@ -0,0 +1,72 @@
+#include <array>
+#include <cstdint>
+
+extern void kernel_main();
+
+struct multiboot2
+{
+    static constexpr std::uint32_t MAGIC    = 0xE85250D6;
+    static constexpr std::uint32_t FLAGS    = 0;
+    static constexpr std::uint32_t LENGTH   = 16;
+    static constexpr std::uint32_t CHECKSUM = -(MAGIC + FLAGS + LENGTH);
+
+    alignas(8)
+    std::uint32_t magic = MAGIC;
+    std::uint32_t flags = FLAGS;
+    std::uint32_t length = LENGTH;
+    std::uint32_t checksum = CHECKSUM;
+} __attribute__((packed));
+
+struct multiboot2_tag
+{
+    alignas(8)
+    std::uint16_t id;
+    std::uint16_t flags;
+    std::uint32_t length;
+    std::uint32_t data[];
+} __attribute__((packed));
+
+__attribute__((section(".multiboot2")))
+multiboot2 multibootHeader;
+
+__attribute__((section(".multiboot2")))
+multiboot2_tag multibootTagInfoRequest = { 
+    1, 0, sizeof(multiboot2_tag) + sizeof(std::uint32_t),
+    {4}
+};
+
+__attribute__((section(".multiboot2")))
+multiboot2_tag multibootTagEnd = { 
+    0, 0, sizeof(multiboot2_tag), {}
+};
+
+alignas(16)
+std::array<std::uint8_t, 16384> stack;
+
+extern "C"
+__attribute__((naked))
+void _start()
+{
+    asm volatile(R"(
+        mov %%eax, multiboot_magic
+        mov %%ebx, multiboot_ptr
+        mov %0, %%esp
+    )" :: "i" (stack.data() + stack.size()));
+
+    extern std::uint32_t __init_array_start;
+    extern std::uint32_t __init_array_end;
+
+    auto it = &__init_array_start;
+    while (it < &__init_array_end) {
+        auto fn = reinterpret_cast<void (*)()>(*it);
+        fn();
+        ++it;
+    }
+
+    kernel_main();
+
+    asm volatile("cli");
+    for (;;)
+        asm volatile("hlt");
+}
+