feat: add ret_from_fork trampoline for newly forked processes

1 files changed, 18 insertions, 1 deletions

diff --git a/na/arch/riscv/trap/swtch.S b/na/arch/riscv/trap/swtch.S
index 8be7904..dbae43d 100644
--- a/na/arch/riscv/trap/swtch.S
+++ b/na/arch/riscv/trap/swtch.S
@@ -76,4 +76,21 @@ kthread_entry_trampoline:
 
     /* kthread_entry should never return, but if it does: */
     wfi
-    j kthread_entry_trampoline + 12  /* loop on wfi */
\ No newline at end of file
+    j kthread_entry_trampoline + 12  /* loop on wfi */
+
+/* ========================================================================
+ * ret_from_fork
+ *
+ * Trampoline for newly forked processes.
+ * Context is set up by fork() so that s0 contains the TrapFrame pointer.
+ *
+ * Calls the MI-layer C++ function:
+ *   void fork_child_entry(TrapFrame* tf);
+ * ======================================================================== */
+    .globl ret_from_fork
+    .align 2
+ret_from_fork:
+    mv a0, s0           /* a0 = TrapFrame pointer */
+    call fork_child_entry /* does not return, eventually calls userret */
+    wfi
+    j ret_from_fork + 8
\ No newline at end of file