riscv32: env call on context switch

src/arch/riscv32.rs

@@ -159,6 +159,12 @@ pub unsafe fn swap(arg: usize, new_sp: StackPointer,
     // Just pass a dummy pointer if we aren't linking the stack
     &mut dummy
   };
+  let stack_limit = if let Some(new_stack) = new_stack {
+    new_stack.limit() as *mut usize
+  } else {
+    // Stack should not reach all the way to address 0
+    0 as *mut usize
+  };
 
   #[naked]
   unsafe extern "C" fn trampoline() {
@@ -174,6 +180,9 @@ pub unsafe fn swap(arg: usize, new_sp: StackPointer,
         .cfi_offset fp, 4
         .cfi_offset ra, 0
 
+        # Perform environment call to modify the PMP regions
+        ecall
+
         # Link the call stacks together by writing the current stack bottom
         # address to the CFA slot in the new stack.
         sw      sp, 0(a3)
@@ -209,6 +218,7 @@ pub unsafe fn swap(arg: usize, new_sp: StackPointer,
       "{a0}" (arg)
       "{a2}" (new_sp.0)
       "{a3}" (new_cfa)
+      "{a7}" (stack_limit)
     :/*"zero",*/"ra",/*"sp","gp","tp",*/"t0","t1","t2",
     /*"fp",*/"s1",/*"a0", "a1"*/"a2", "a3", "a4", "a5",
       "a6", "a7", "s2",  "s3",  "s4", "s5", "s6", "s7",