(mark_byte_stack): Add a comment.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/bytecode.c b/src/bytecode.c
index 22c41920cc7..a99860bd8cd 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -272,6 +272,13 @@ mark_byte_stack ()
 
   for (stack = byte_stack_list; stack; stack = stack->next)
     {
+      /* If STACK->top is null here, this means there's an opcode in
+         Fbyte_code that wasn't expected to GC, but did.  To find out
+         which opcode this is, record the value of `stack', and walk
+         up the stack in a debugger, stopping in frames of Fbyte_code.
+         The culprit is found in the frame of Fbyte_code where the
+         address of its local variable `stack' is equal to the
+         recorded value of `stack' here.  */
       if (!stack->top)
         abort ();