rt: Be more precise with VALGRIND_MAKE_MEM_UNDEFINED

1 files changed, 5 insertions, 3 deletions

diff --git a/src/rt/rust_stack.cpp b/src/rt/rust_stack.cpp
index b5a83832f08..0522b3b9847 100644
--- a/src/rt/rust_stack.cpp
+++ b/src/rt/rust_stack.cpp
@@ -17,13 +17,15 @@ register_valgrind_stack(stk_seg *stk) {
 }
 
 void
-prepare_valgrind_stack(stk_seg *stk) {
+reuse_valgrind_stack(stk_seg *stk, uint8_t *sp) {
 #ifndef NVALGRIND
     // Establish that the stack is accessible.  This must be done when reusing
     // old stack segments, since the act of popping the stack previously
     // caused valgrind to consider the whole thing inaccessible.
-    size_t sz = stk->end - (uintptr_t)&stk->data[0];
-    VALGRIND_MAKE_MEM_UNDEFINED(stk->data, sz);
+    assert(sp >= stk->data && sp <= (uint8_t*) stk->end
+	   && "Stack pointer must be inside stack segment");
+    size_t sz = stk->end - (uintptr_t)sp;
+    VALGRIND_MAKE_MEM_UNDEFINED(sp, sz);
 #endif
 }