Use ‘const’ to clarify GC marking

Add ‘const’ to make the GC marking code a bit clearer.
This can also help the compiler in some cases, I think because
GCC can now determine more often that the value of a static C
variable can be cached when its address is now converted to
‘Lisp Object const *’ before escaping.
* src/alloc.c (staticvec, mark_maybe_objects, mark_memory)
(mark_stack, staticpro, mark_object_root_visitor)
(garbage_collect_1):
* src/pdumper.c (dump_ptr_referrer, dump_emacs_reloc_to_lv)
(dump_emacs_reloc_to_emacs_ptr_raw, dump_root_visitor):
* src/lisp.h (vcopy, struct gc_root_visitor):
* src/sysdep.c (stack_overflow):
* src/thread.c (mark_one_thread):
* src/thread.h (struct thread_state):
Use pointer-to-const instead of plain pointer in some
GC-related places where either will do.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/thread.h b/src/thread.h
index e46545baf27..cb7e60f21f8 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -65,7 +65,7 @@ struct thread_state
   /* m_stack_bottom must be the first non-Lisp field.  */
   /* An address near the bottom of the stack.
      Tells GC how to save a copy of the stack.  */
-  char *m_stack_bottom;
+  char const *m_stack_bottom;
 #define stack_bottom (current_thread->m_stack_bottom)
 
   /* The address of an object near the C stack top, used to determine
@@ -75,7 +75,7 @@ struct thread_state
      error in Emacs.  If the C function F calls G which calls H which
      calls ... F, then at least one of the functions in the chain
      should set this to the address of a local variable.  */
-  void *stack_top;
+  void const *stack_top;
 
   struct catchtag *m_catchlist;
 #define catchlist (current_thread->m_catchlist)