Add support for user callbacks

src/windows-emulator/user_callback_dispatch.hpp

@@ -0,0 +1,46 @@
+#pragma once
+
+#include "syscall_utils.hpp"
+
+// TODO: Here we are calling guest functions directly, but this is not how it works in the real Windows kernel.
+//       In the real implementation, the kernel invokes ntdll!KiUserCallbackDispatcher and passes a callback
+//       index that refers to an entry in PEB->KernelCallbackTable. The dispatcher then looks up the function
+//       pointer in that table and invokes the corresponding user-mode callback.
+
+template <typename... Args>
+void dispatch_user_callback(const syscall_context& c, callback_id completion_id, uint64_t func_address, Args... args)
+{
+    const uint64_t original_rsp = c.emu.read_stack_pointer();
+
+    // Save syscall argument registers BEFORE modifying anything
+    const callback_frame frame{
+        .handler_id = completion_id,
+        .rip = c.emu.read_instruction_pointer(),
+        .rsp = original_rsp,
+        .r10 = c.emu.reg(x86_register::r10),
+        .rcx = c.emu.reg(x86_register::rcx),
+        .rdx = c.emu.reg(x86_register::rdx),
+        .r8 = c.emu.reg(x86_register::r8),
+        .r9 = c.emu.reg(x86_register::r9),
+    };
+
+    uint64_t stack_ptr = align_down(original_rsp, 16);
+
+    constexpr size_t arg_count = sizeof...(Args);
+    const size_t allocation_size = aligned_stack_space(arg_count);
+    stack_ptr -= allocation_size;
+
+    // Push the return address onto the stack (Simulating CALL)
+    stack_ptr -= sizeof(emulator_pointer);
+    c.emu.write_memory(stack_ptr, &c.proc.callback_sentinel_addr, sizeof(c.proc.callback_sentinel_addr));
+
+    c.proc.active_thread->callback_stack.push_back(frame);
+
+    c.emu.reg(x86_register::rsp, stack_ptr);
+
+    size_t index = 0;
+    (set_function_argument(c.emu, index++, static_cast<uint64_t>(args)), ...);
+
+    c.emu.reg(x86_register::rip, func_address);
+    c.run_callback = true;
+}