rt: Make the stack canary just a word on the stk_seg struct

2 files changed, 12 insertions, 13 deletions

diff --git a/src/rt/rust_stack.cpp b/src/rt/rust_stack.cpp
index 84e4215ac67..37acc438672 100644
--- a/src/rt/rust_stack.cpp
+++ b/src/rt/rust_stack.cpp
@@ -3,6 +3,12 @@
 #include "vg/valgrind.h"
 #include "vg/memcheck.h"
 
+#ifdef _LP64
+const uintptr_t canary_value = 0xABCDABCDABCDABCD;
+#else
+const uintptr_t canary_value = 0xABCDABCD;
+#endif
+
 void
 register_valgrind_stack(stk_seg *stk) {
     stk->valgrind_id =
@@ -17,8 +23,7 @@ prepare_valgrind_stack(stk_seg *stk) {
     // 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 + sizeof(stack_canary),
-                                sz - sizeof(stack_canary));
+    VALGRIND_MAKE_MEM_UNDEFINED(stk->data, sz);
 #endif
 }
 
@@ -29,12 +34,10 @@ deregister_valgrind_stack(stk_seg *stk) {
 
 void
 add_stack_canary(stk_seg *stk) {
-    memcpy(stk->data, stack_canary, sizeof(stack_canary));
-    assert(sizeof(stack_canary) == 16 && "Stack canary was not the expected size");
+    stk->canary = canary_value;
 }
 
 void
 check_stack_canary(stk_seg *stk) {
-    assert(!memcmp(stk->data, stack_canary, sizeof(stack_canary))
-      && "Somebody killed the canary");
+    assert(stk->canary == canary_value && "Somebody killed the canary");
 }
diff --git a/src/rt/rust_stack.h b/src/rt/rust_stack.h
index f6704a9f0eb..e8be2f2c083 100644
--- a/src/rt/rust_stack.h
+++ b/src/rt/rust_stack.h
@@ -10,15 +10,11 @@ struct stk_seg {
     uint32_t pad;
 #endif
 
+    uintptr_t canary;
+
     uint8_t data[];
 };
 
-// A value that goes at the end of the stack and must not be touched
-const uint8_t stack_canary[] = {0xAB, 0xCD, 0xAB, 0xCD,
-                                0xAB, 0xCD, 0xAB, 0xCD,
-                                0xAB, 0xCD, 0xAB, 0xCD,
-                                0xAB, 0xCD, 0xAB, 0xCD};
-
 // Used by create_stack
 void
 register_valgrind_stack(stk_seg *stk);
@@ -34,7 +30,7 @@ add_stack_canary(stk_seg *stk);
 template <class T>
 stk_seg *
 create_stack(T allocer, size_t sz) {
-  size_t total_sz = sizeof(stk_seg) + sz + sizeof(stack_canary);
+  size_t total_sz = sizeof(stk_seg) + sz;
   stk_seg *stk = (stk_seg *)allocer->malloc(total_sz, "stack");
   memset(stk, 0, sizeof(stk_seg));
   stk->end = (uintptr_t) &stk->data[sz];