feat: make kernel architecture-agnostic; primitive work on arm port

kernel/src/Arch/aarch64/Platform.cpp

@@ -0,0 +1,64 @@
+/*
+    * Platform.cpp
+    * aarch64 bring-up hooks (implements Arch/Platform.hpp)
+    * Copyright (c) 2026 Daniel Hammer
+*/
+
+#include <Arch/Platform.hpp>
+#include <Arch/Cpu.hpp>
+#include <Arch/Smp.hpp>
+#include <Terminal/Terminal.hpp>
+#include <CppLib/Stream.hpp>
+
+using namespace Kt;
+
+namespace Arch {
+
+    void EarlyInitialize() {
+        // No per-CPU data yet: Smp::TryGetCurrentCpuData must see null.
+        asm volatile("msr tpidr_el1, xzr");
+
+        // CPACR_EL1.FPEN = 0b11: FP/SIMD usable at EL0 and EL1 (the kernel
+        // itself is built -mgeneral-regs-only; Context.S saves user state).
+        uint64_t cpacr;
+        asm volatile("mrs %0, cpacr_el1" : "=r"(cpacr));
+        cpacr |= 3ULL << 20;
+        asm volatile("msr cpacr_el1, %0\n\tisb" :: "r"(cpacr));
+    }
+
+    // TODO(aarch64): install the VBAR_EL1 vector table (EL1/EL0 synchronous
+    // exceptions -> panic / SyscallDispatch, IRQ -> GIC -> ArchIrqDispatch).
+    void InitializeTraps() {
+        KernelLogStream(WARNING, "Arch") << "aarch64: exception vectors not implemented";
+    }
+
+    // MAIR_EL1 attribute indices are chosen together with the page-table
+    // format (Paging.cpp), so there is nothing to program separately.
+    void InitializeMemoryAttributes() {
+    }
+
+    // TODO(aarch64): GIC distributor/redistributor from the ACPI MADT.
+    void InitializeInterrupts(Hal::ACPI::CommonSDTHeader*) {
+        Smp::InitBsp();
+        KernelLogStream(WARNING, "Arch") << "aarch64: no interrupt controller driver";
+    }
+
+    void InitializePlatformDevices() {
+    }
+
+    // EL0 entry needs no global state beyond Arch::ActivateThread.
+    void PrepareUserMode() {
+    }
+
+    void LateInitialize() {
+    }
+
+    void ListPlatformDevices(PlatformDeviceSink, void*) {
+    }
+
+    // TODO(aarch64): PSCI SYSTEM_RESET through the conduit the FADT names.
+    void Reboot() {
+        HaltForever();
+    }
+
+}