feat: add initial RISC-V architecture support and core kernel functionality

- Implement MMU hardware primitives for RISC-V SV39 in mmu.h
- Create trap vector control primitives in trap.h
- Define trap frame structure for RISC-V in trapframe.h
- Add assembly routines for context switching in swtch.S
- Implement trap vector entry/exit in trap_vector.S
- Introduce basic error number definitions in errno.h
- Provide placement new/delete operators in new.h
- Define kernel panic handler in panic.h and implement in panic.cc
- Establish basic type definitions in types.h
- Create the kernel main entry point in main.cc with global initialization
- Add synchronization primitives using spinlocks in spinlock.h and spinlock.cc
- Define per-CPU state tracking for interrupts in cpu_state.h
- Create a linker script for the kernel in linker.ld
- Update module makefiles for kernel and library components

1 files changed, 46 insertions, 0 deletions

diff --git a/na/lib/panic.cc b/na/lib/panic.cc
new file mode 100644
index 0000000..4745272
--- /dev/null
+++ b/na/lib/panic.cc
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/*
+ * Kernel Panic — minimal fatal error handler.
+ *
+ * Before console_init(): silent death (no UART).
+ * After console_init():  prints message then halts.
+ *
+ * Reference: docs/specs/global_init.md §6
+ */
+
+#include <lume/types.h>
+#include <arch/cpu.h>
+
+// Minimal direct UART output (same as main.cc early boot)
+// This can be used by other early-boot code before console_init()
+
+constexpr uint64 kUart0VA = 0x10000000UL + 0xFFFFFFC000000000ULL;
+
+extern "C" void early_putc(char c) {
+    volatile auto* uart = reinterpret_cast<volatile uint8*>(kUart0VA);
+    *uart = static_cast<uint8>(c);
+}
+
+extern "C" void early_puts(const char* s) {
+    while (*s) early_putc(*s++);
+}
+
+extern "C" [[noreturn]] void kernel_panic(const char* msg, const char* detail) {
+    arch::cpu::intr_off();
+
+    early_puts("\n*** KERNEL PANIC: ");
+    if (msg) {
+        early_puts(msg);
+    }
+    if (detail) {
+        early_puts(": ");
+        early_puts(detail);
+    }
+    early_puts(" ***\n");
+
+    while (true) {
+        arch::cpu::halt_until_interrupt();
+    }
+}