feat: add RISC-V configuration and memory management enhancements

Co-authored-by: Copilot <copilot@github.com>

1 files changed, 42 insertions, 3 deletions

diff --git a/na/arch/riscv/trap/swtch.S b/na/arch/riscv/trap/swtch.S
index 4393505..8be7904 100644
--- a/na/arch/riscv/trap/swtch.S
+++ b/na/arch/riscv/trap/swtch.S
@@ -1,11 +1,28 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 /* Copyright (C) 2026 Richard Qin */
 
+/*
+ * Context Switch & Kernel Thread Trampoline (RISC-V 64)
+ *
+ * context_switch: saves/restores callee-saved registers.
+ * kthread_entry_trampoline: entry point for newly created kernel threads.
+ *   After context_switch loads the new Context, execution lands here via
+ *   Context.ra = kthread_entry_trampoline. The entry function and argument
+ *   are in s0 and s1 respectively, set by sched_init/create_tcb.
+ *
+ * The trampoline calls the MI-layer kthread_entry(entry, arg).
+ *
+ * Reference: docs/specs/scheduler.md §6
+ */
+
     .section .text
+
+/* ========================================================================
+ * void context_switch(Context* old_ctx, Context* next_ctx);
+ *   a0 = old_ctx_ptr, a1 = next_ctx_ptr
+ * ======================================================================== */
     .globl context_switch
     .align 2
-# void context_switch(Context* old_ctx, Context* next_ctx);
-# a0 = old_ctx_ptr, a1 = next_ctx_ptr
 context_switch:
     sd ra, 0(a0)
     sd sp, 8(a0)
@@ -37,4 +54,26 @@ context_switch:
     ld s10, 96(a1)
     ld s11, 104(a1)
 
-    ret
\ No newline at end of file
+    ret
+
+/* ========================================================================
+ * kthread_entry_trampoline
+ *
+ * Reached via context_switch when a new kthread is first scheduled.
+ * Context was set up by create_tcb():
+ *   s0 = entry function pointer
+ *   s1 = argument pointer
+ *
+ * Calls the MI-layer C++ function:
+ *   void kthread_entry(void (*entry)(void*), void* arg);
+ * ======================================================================== */
+    .globl kthread_entry_trampoline
+    .align 2
+kthread_entry_trampoline:
+    mv a0, s0           /* a0 = entry function */
+    mv a1, s1           /* a1 = argument */
+    call kthread_entry  /* MI-layer C++ function */
+
+    /* kthread_entry should never return, but if it does: */
+    wfi
+    j kthread_entry_trampoline + 12  /* loop on wfi */
\ No newline at end of file