Merging upstream version 115.12.0esr.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/xpcom/reflect/xptcall/md/unix/xptcinvoke_arm.cpp b/xpcom/reflect/xptcall/md/unix/xptcinvoke_arm.cpp
index 39a6b406f4..d66f300649 100644
--- a/xpcom/reflect/xptcall/md/unix/xptcinvoke_arm.cpp
+++ b/xpcom/reflect/xptcall/md/unix/xptcinvoke_arm.cpp
@@ -164,6 +164,18 @@ NS_InvokeByIndex(nsISupports* that, uint32_t methodIndex,
   vtable = *reinterpret_cast<vtable_func **>(that);
   func = vtable[methodIndex];
 
+/* !!! IMPORTANT !!!
+ * In the case of paramCount = 0 (and also some other cases in practice but
+ * the compiler doesn't know about them), the stack_space is not initialized.
+ * Reading the stack_space is technically undefined behavior, but practically,
+ * the values we read from there only matter to the called function when they
+ * are initialized.
+ * The asm volatile block makes the compiler ignore that the stack_space
+ * may not be initialized, avoiding it optimizing away e.g. the first loop
+ * test in invoke_copy_to_stack.
+ */
+  asm volatile(";");
+
   return func(that, stack_space[base_size * 2 - 3],
                     stack_space[base_size * 2 - 2],
                     stack_space[base_size * 2 - 1]);