* ada-exp.y (write_object_renaming, write_var_or_type)

	(write_ambiguous_var, write_var_from_sym): Make blocks const.
	* ada-lang.c (replace_operator_with_call)
	(find_old_style_renaming_symbol): Make blocks const.
	* ada-lang.h (ada_find_renaming_symbol): Update.
	(struct ada_symbol_info) <block>: Now const.
	* breakpoint.c (watch_command_1): Update.
	* breakpoint.h (struct watchpoint) <exp_valid_block,
	cond_exp_valid_block>: Now const.
	* c-exp.y (classify_inner_name, classify_name): Make block
	argument const.
	* expprint.c (print_subexp_standard) <OP_VAR_VALUE>: Make 'b'
	const.
	* expression.h (innermost_block, parse_exp_1): Update.
	(union exp_element) <block>: Now const.
	* gdbtypes.c (lookup_template_type, lookup_enum, lookup_union)
	(lookup_struct): Make block argument const.
	* gdbtypes.h (lookup_template_type): Update.
	* go-exp.y (classify_name, classify_packaged_name)
	(package_name_p): Make block argument const.
	* objc-lang.c (lookup_struct_typedef): Make block argument const.
	* objc-lang.h (lookup_struct_typedef): Update.
	* parse.c (parse_exp_in_context, parse_exp_1)
	(write_exp_elt_block): Make block arguments const.
	(expression_context_block, innermost_block): Now const.
	* parser-defs.h (write_exp_elt_block): Update.
	(expression_context_block, innermost_block, block_found): Now
	const.
	* printcmd.c (struct display) <block>: Now const.
	* symtab.h (lookup_struct, lookup_union, lookup_enum): Update.
	* valops.c (address_of_variable): Make block argument const.
	* value.h (value_of_variable): Update.
	* varobj.c (struct varobj_root) <valid_block>: Now const.

22 files changed, 93 insertions, 54 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 72423fbc3a1..5e2a263a86e 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,39 @@
+2012-12-03  Tom Tromey  <tromey@redhat.com>
+
+	* ada-exp.y (write_object_renaming, write_var_or_type)
+	(write_ambiguous_var, write_var_from_sym): Make blocks const.
+	* ada-lang.c (replace_operator_with_call)
+	(find_old_style_renaming_symbol): Make blocks const.
+	* ada-lang.h (ada_find_renaming_symbol): Update.
+	(struct ada_symbol_info) <block>: Now const.
+	* breakpoint.c (watch_command_1): Update.
+	* breakpoint.h (struct watchpoint) <exp_valid_block,
+	cond_exp_valid_block>: Now const.
+	* c-exp.y (classify_inner_name, classify_name): Make block
+	argument const.
+	* expprint.c (print_subexp_standard) <OP_VAR_VALUE>: Make 'b'
+	const.
+	* expression.h (innermost_block, parse_exp_1): Update.
+	(union exp_element) <block>: Now const.
+	* gdbtypes.c (lookup_template_type, lookup_enum, lookup_union)
+	(lookup_struct): Make block argument const.
+	* gdbtypes.h (lookup_template_type): Update.
+	* go-exp.y (classify_name, classify_packaged_name)
+	(package_name_p): Make block argument const.
+	* objc-lang.c (lookup_struct_typedef): Make block argument const.
+	* objc-lang.h (lookup_struct_typedef): Update.
+	* parse.c (parse_exp_in_context, parse_exp_1)
+	(write_exp_elt_block): Make block arguments const.
+	(expression_context_block, innermost_block): Now const.
+	* parser-defs.h (write_exp_elt_block): Update.
+	(expression_context_block, innermost_block, block_found): Now
+	const.
+	* printcmd.c (struct display) <block>: Now const.
+	* symtab.h (lookup_struct, lookup_union, lookup_enum): Update.
+	* valops.c (address_of_variable): Make block argument const.
+	* value.h (value_of_variable): Update.
+	* varobj.c (struct varobj_root) <valid_block>: Now const.
+
 2012-11-30  Yao Qi  <yao@codesourcery.com>
 
 	* breakpoint.c (print_one_breakpoint_location): Indent code.
diff --git a/gdb/ada-exp.y b/gdb/ada-exp.y
index 1a80b0b1fe4..57c7d86e62b 100644
--- a/gdb/ada-exp.y
+++ b/gdb/ada-exp.y
@@ -130,10 +130,10 @@ static struct stoken string_to_operator (struct stoken);
 
 static void write_int (LONGEST, struct type *);
 
-static void write_object_renaming (struct block *, const char *, int,
+static void write_object_renaming (const struct block *, const char *, int,
 				   const char *, int);
 
-static struct type* write_var_or_type (struct block *, struct stoken);
+static struct type* write_var_or_type (const struct block *, struct stoken);
 
 static void write_name_assoc (struct stoken);
 
@@ -143,7 +143,7 @@ static struct block *block_lookup (struct block *, char *);
 
 static LONGEST convert_char_literal (struct type *, LONGEST);
 
-static void write_ambiguous_var (struct block *, char *, int);
+static void write_ambiguous_var (const struct block *, char *, int);
 
 static struct type *type_int (void);
 
@@ -818,8 +818,8 @@ string_to_operator (struct stoken string)
 /* Emit expression to access an instance of SYM, in block BLOCK (if
  * non-NULL), and with :: qualification ORIG_LEFT_CONTEXT.  */
 static void
-write_var_from_sym (struct block *orig_left_context,
-		    struct block *block,
+write_var_from_sym (const struct block *orig_left_context,
+		    const struct block *block,
 		    struct symbol *sym)
 {
   if (orig_left_context == NULL && symbol_read_needs_frame (sym))
@@ -867,7 +867,7 @@ write_exp_op_with_string (enum exp_opcode opcode, struct stoken token)
  * new encoding entirely (FIXME pnh 7/20/2007).  */
 
 static void
-write_object_renaming (struct block *orig_left_context,
+write_object_renaming (const struct block *orig_left_context,
 		       const char *renamed_entity, int renamed_entity_len,
 		       const char *renaming_expr, int max_depth)
 {
@@ -1161,7 +1161,7 @@ write_selectors (char *sels)
    a temporary symbol that is valid until the next call to ada_parse.
    */
 static void
-write_ambiguous_var (struct block *block, char *name, int len)
+write_ambiguous_var (const struct block *block, char *name, int len)
 {
   struct symbol *sym =
     obstack_alloc (&temp_parse_space, sizeof (struct symbol));
@@ -1253,7 +1253,7 @@ get_symbol_field_type (struct symbol *sym, char *encoded_field_name)
    identifier).  */
 
 static struct type*
-write_var_or_type (struct block *block, struct stoken name0)
+write_var_or_type (const struct block *block, struct stoken name0)
 {
   int depth;
   char *encoded_name;
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index deefcfb291e..b03b2a2c7be 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -128,7 +128,7 @@ static struct value *resolve_subexp (struct expression **, int *, int,
                                      struct type *);
 
 static void replace_operator_with_call (struct expression **, int, int, int,
-                                        struct symbol *, struct block *);
+                                        struct symbol *, const struct block *);
 
 static int possible_user_operator_p (enum exp_opcode, struct value **);
 
@@ -150,7 +150,7 @@ static enum ada_renaming_category parse_old_style_renaming (struct type *,
 							    const char **);
 
 static struct symbol *find_old_style_renaming_symbol (const char *,
-						      struct block *);
+						      const struct block *);
 
 static struct type *ada_lookup_struct_elt_type (struct type *, char *,
                                                 int, int, int *);
@@ -3719,7 +3719,7 @@ get_selections (int *choices, int n_choices, int max_results,
 static void
 replace_operator_with_call (struct expression **expp, int pc, int nargs,
                             int oplen, struct symbol *sym,
-                            struct block *block)
+                            const struct block *block)
 {
   /* A new expression, with 6 more elements (3 for funcall, 4 for function
      symbol, -oplen for operator being replaced).  */
@@ -4232,7 +4232,7 @@ lookup_cached_symbol (const char *name, domain_enum namespace,
 
 static void
 cache_symbol (const char *name, domain_enum namespace, struct symbol *sym,
-              struct block *block)
+              const struct block *block)
 {
 }
 
@@ -4805,7 +4805,7 @@ remove_irrelevant_renamings (struct ada_symbol_info *syms,
   for (i = 0; i < nsyms; i += 1)
     {
       struct symbol *sym = syms[i].sym;
-      struct block *block = syms[i].block;
+      const struct block *block = syms[i].block;
       const char *name;
       const char *suffix;
 
@@ -7195,7 +7195,7 @@ ada_find_any_type (const char *name)
    Return symbol if found, and NULL otherwise.  */
 
 struct symbol *
-ada_find_renaming_symbol (struct symbol *name_sym, struct block *block)
+ada_find_renaming_symbol (struct symbol *name_sym, const struct block *block)
 {
   const char *name = SYMBOL_LINKAGE_NAME (name_sym);
   struct symbol *sym;
@@ -7217,7 +7217,7 @@ ada_find_renaming_symbol (struct symbol *name_sym, struct block *block)
 }
 
 static struct symbol *
-find_old_style_renaming_symbol (const char *name, struct block *block)
+find_old_style_renaming_symbol (const char *name, const struct block *block)
 {
   const struct symbol *function_sym = block_linkage_function (block);
   char *rename;
diff --git a/gdb/ada-lang.h b/gdb/ada-lang.h
index f6154fde09a..ab6997dd74f 100644
--- a/gdb/ada-lang.h
+++ b/gdb/ada-lang.h
@@ -90,7 +90,7 @@ struct ada_symbol_info
   struct symbol *sym;
 
   /* The block where the symbol was found.  */
-  struct block *block;
+  const struct block *block;
 };
 
 /* Denotes a type of renaming symbol (see ada_parse_renaming).  */
@@ -342,7 +342,7 @@ extern struct type *ada_find_parallel_type (struct type *,
 extern LONGEST get_int_var_value (char *, int *);
 
 extern struct symbol *ada_find_renaming_symbol (struct symbol *name_sym,
-                                                struct block *block);
+                                                const struct block *block);
 
 extern int ada_prefer_type (struct type *, struct type *);
 
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index 59b7bf32766..01a472c6317 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -10750,7 +10750,7 @@ watch_command_1 (char *arg, int accessflag, int from_tty,
   volatile struct gdb_exception e;
   struct breakpoint *b, *scope_breakpoint = NULL;
   struct expression *exp;
-  struct block *exp_valid_block = NULL, *cond_exp_valid_block = NULL;
+  const struct block *exp_valid_block = NULL, *cond_exp_valid_block = NULL;
   struct value *val, *mark, *result;
   struct frame_info *frame;
   char *exp_start = NULL;
diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
index 8b1bcb73772..546e85514ed 100644
--- a/gdb/breakpoint.h
+++ b/gdb/breakpoint.h
@@ -756,12 +756,12 @@ struct watchpoint
   struct expression *exp;
   /* The largest block within which it is valid, or NULL if it is
      valid anywhere (e.g. consists just of global symbols).  */
-  struct block *exp_valid_block;
+  const struct block *exp_valid_block;
   /* The conditional expression if any.  */
   struct expression *cond_exp;
   /* The largest block within which it is valid, or NULL if it is
      valid anywhere (e.g. consists just of global symbols).  */
-  struct block *cond_exp_valid_block;
+  const struct block *cond_exp_valid_block;
   /* Value of the watchpoint the last time we checked it, or NULL when
      we do not know the value yet or the value was not readable.  VAL
      is never lazy.  */
diff --git a/gdb/c-exp.y b/gdb/c-exp.y
index 11eaadbdf88..05d12be7948 100644
--- a/gdb/c-exp.y
+++ b/gdb/c-exp.y
@@ -2699,7 +2699,7 @@ static struct obstack name_obstack;
    in which lookups start; this can be NULL to mean the global
    scope.  */
 static int
-classify_name (struct block *block)
+classify_name (const struct block *block)
 {
   struct symbol *sym;
   char *copy;
@@ -2791,7 +2791,7 @@ classify_name (struct block *block)
    in `yylval' is the first component of a name, false otherwise.  */
 
 static int
-classify_inner_name (struct block *block, int first_name)
+classify_inner_name (const struct block *block, int first_name)
 {
   struct type *type, *new_type;
   char *copy;
diff --git a/gdb/expprint.c b/gdb/expprint.c
index ddd3a77c77c..b68fbeef436 100644
--- a/gdb/expprint.c
+++ b/gdb/expprint.c
@@ -122,7 +122,7 @@ print_subexp_standard (struct expression *exp, int *pos,
 
     case OP_VAR_VALUE:
       {
-	struct block *b;
+	const struct block *b;
 
 	(*pos) += 3;
 	b = exp->elts[pc + 1].block;
diff --git a/gdb/expression.h b/gdb/expression.h
index 004a60e85c2..3b70ef3f410 100644
--- a/gdb/expression.h
+++ b/gdb/expression.h
@@ -73,7 +73,7 @@ union exp_element
     char string;
     struct type *type;
     struct internalvar *internalvar;
-    struct block *block;
+    const struct block *block;
     struct objfile *objfile;
   };
 
@@ -100,8 +100,8 @@ extern struct expression *parse_expression (char *);
 
 extern struct type *parse_field_expression (char *, char **);
 
-extern struct expression *parse_exp_1 (char **, CORE_ADDR pc, struct block *,
-				       int);
+extern struct expression *parse_exp_1 (char **, CORE_ADDR pc,
+				       const struct block *, int);
 
 /* For use by parsers; set if we want to parse an expression and
    attempt to complete a field name.  */
@@ -110,7 +110,7 @@ extern int in_parse_field;
 /* The innermost context required by the stack and register variables
    we've encountered so far.  To use this, set it to NULL, then call
    parse_<whatever>, then look at it.  */
-extern struct block *innermost_block;
+extern const struct block *innermost_block;
 
 /* From eval.c */
 
diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index d3220041759..ceb52a55d38 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -1234,7 +1234,7 @@ lookup_signed_typename (const struct language_defn *language,
    visible in lexical block BLOCK.  */
 
 struct type *
-lookup_struct (const char *name, struct block *block)
+lookup_struct (const char *name, const struct block *block)
 {
   struct symbol *sym;
 
@@ -1256,7 +1256,7 @@ lookup_struct (const char *name, struct block *block)
    visible in lexical block BLOCK.  */
 
 struct type *
-lookup_union (const char *name, struct block *block)
+lookup_union (const char *name, const struct block *block)
 {
   struct symbol *sym;
   struct type *t;
@@ -1280,7 +1280,7 @@ lookup_union (const char *name, struct block *block)
    visible in lexical block BLOCK.  */
 
 struct type *
-lookup_enum (const char *name, struct block *block)
+lookup_enum (const char *name, const struct block *block)
 {
   struct symbol *sym;
 
@@ -1302,7 +1302,7 @@ lookup_enum (const char *name, struct block *block)
 
 struct type *
 lookup_template_type (char *name, struct type *type, 
-		      struct block *block)
+		      const struct block *block)
 {
   struct symbol *sym;
   char *nam = (char *) 
diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h
index b23df9ae42f..fb113d21b91 100644
--- a/gdb/gdbtypes.h
+++ b/gdb/gdbtypes.h
@@ -1543,7 +1543,7 @@ extern struct type *lookup_typename (const struct language_defn *,
 				     const struct block *, int);
 
 extern struct type *lookup_template_type (char *, struct type *,
-					  struct block *);
+					  const struct block *);
 
 extern int get_vptr_fieldno (struct type *, struct type **);
 
diff --git a/gdb/go-exp.y b/gdb/go-exp.y
index c3171c381b7..18669fc6853 100644
--- a/gdb/go-exp.y
+++ b/gdb/go-exp.y
@@ -1362,7 +1362,7 @@ build_packaged_name (const char *package, int package_len,
    to mean the global scope.  */
 
 static int
-package_name_p (const char *name, struct block *block)
+package_name_p (const char *name, const struct block *block)
 {
   struct symbol *sym;
   int is_a_field_of_this;
@@ -1402,7 +1402,7 @@ classify_unsafe_function (struct stoken function_name)
    The result is one of NAME, NAME_OR_INT, or TYPENAME.  */
 
 static int
-classify_packaged_name (struct block *block)
+classify_packaged_name (const struct block *block)
 {
   char *copy;
   struct symbol *sym;
@@ -1430,7 +1430,7 @@ classify_packaged_name (struct block *block)
    The result is one of NAME, NAME_OR_INT, or TYPENAME.  */
 
 static int
-classify_name (struct block *block)
+classify_name (const struct block *block)
 {
   struct type *type;
   struct symbol *sym;
diff --git a/gdb/objc-lang.c b/gdb/objc-lang.c
index e42a03c6aa1..2dbaffdb021 100644
--- a/gdb/objc-lang.c
+++ b/gdb/objc-lang.c
@@ -82,7 +82,7 @@ static const struct objfile_data *objc_objfile_data;
    suitably defined.  */
 
 struct symbol *
-lookup_struct_typedef (char *name, struct block *block, int noerr)
+lookup_struct_typedef (char *name, const struct block *block, int noerr)
 {
   struct symbol *sym;
 
diff --git a/gdb/objc-lang.h b/gdb/objc-lang.h
index 1feeca4fa6a..47fbae9ff7a 100644
--- a/gdb/objc-lang.h
+++ b/gdb/objc-lang.h
@@ -46,7 +46,7 @@ extern void start_msglist (void);
 extern void add_msglist (struct stoken *str, int addcolon);
 extern int end_msglist (void);
 
-struct symbol *lookup_struct_typedef (char *name, struct block *block,
+struct symbol *lookup_struct_typedef (char *name, const struct block *block,
 				      int noerr);
 
 #endif
diff --git a/gdb/parse.c b/gdb/parse.c
index afe1c18492c..0392c6a3652 100644
--- a/gdb/parse.c
+++ b/gdb/parse.c
@@ -71,9 +71,9 @@ const struct exp_descriptor exp_descriptor_standard =
 struct expression *expout;
 int expout_size;
 int expout_ptr;
-struct block *expression_context_block;
+const struct block *expression_context_block;
 CORE_ADDR expression_context_pc;
-struct block *innermost_block;
+const struct block *innermost_block;
 int arglist_len;
 static struct type_stack type_stack;
 char *lexptr;
@@ -116,7 +116,7 @@ static int prefixify_subexp (struct expression *, struct expression *, int,
 			     int);
 
 static struct expression *parse_exp_in_context (char **, CORE_ADDR,
-						struct block *, int, 
+						const struct block *, int, 
 						int, int *);
 
 void _initialize_parse (void);
@@ -248,7 +248,7 @@ write_exp_elt_sym (struct symbol *expelt)
 }
 
 void
-write_exp_elt_block (struct block *b)
+write_exp_elt_block (const struct block *b)
 {
   union exp_element tmp;
 
@@ -1097,7 +1097,8 @@ prefixify_subexp (struct expression *inexpr,
    If COMMA is nonzero, stop if a comma is reached.  */
 
 struct expression *
-parse_exp_1 (char **stringptr, CORE_ADDR pc, struct block *block, int comma)
+parse_exp_1 (char **stringptr, CORE_ADDR pc, const struct block *block,
+	     int comma)
 {
   return parse_exp_in_context (stringptr, pc, block, comma, 0, NULL);
 }
@@ -1110,7 +1111,7 @@ parse_exp_1 (char **stringptr, CORE_ADDR pc, struct block *block, int comma)
    is left untouched.  */
 
 static struct expression *
-parse_exp_in_context (char **stringptr, CORE_ADDR pc, struct block *block,
+parse_exp_in_context (char **stringptr, CORE_ADDR pc, const struct block *block,
 		      int comma, int void_context_p, int *out_subexp)
 {
   volatile struct gdb_exception except;
diff --git a/gdb/parser-defs.h b/gdb/parser-defs.h
index c889d56e0b0..6dd5329b6a4 100644
--- a/gdb/parser-defs.h
+++ b/gdb/parser-defs.h
@@ -41,7 +41,7 @@ extern int expout_ptr;
 /* If this is nonzero, this block is used as the lexical context
    for symbol names.  */
 
-extern struct block *expression_context_block;
+extern const struct block *expression_context_block;
 
 /* If expression_context_block is non-zero, then this is the PC within
    the block that we want to evaluate expressions at.  When debugging
@@ -51,12 +51,12 @@ extern CORE_ADDR expression_context_pc;
 
 /* The innermost context required by the stack and register variables
    we've encountered so far.  */
-extern struct block *innermost_block;
+extern const struct block *innermost_block;
 
 /* The block in which the most recently discovered symbol was found.
    FIXME: Should be declared along with lookup_symbol in symtab.h; is not
    related specifically to parsing.  */
-extern struct block *block_found;
+extern const struct block *block_found;
 
 /* Number of arguments seen so far in innermost function call.  */
 extern int arglist_len;
@@ -191,7 +191,7 @@ void write_exp_string_vector (int type, struct stoken_vector *vec);
 
 extern void write_exp_bitstring (struct stoken);
 
-extern void write_exp_elt_block (struct block *);
+extern void write_exp_elt_block (const struct block *);
 
 extern void write_exp_elt_objfile (struct objfile *objfile);
 
diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index 7a669f125e0..143bd0eaec8 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -145,7 +145,7 @@ struct display
     struct program_space *pspace;
 
     /* Innermost block required by this expression when evaluated.  */
-    struct block *block;
+    const struct block *block;
 
     /* Status of this display (enabled or disabled).  */
     int enabled_p;
diff --git a/gdb/symtab.c b/gdb/symtab.c
index c4bd13da8d2..dee47a97b1b 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -62,6 +62,7 @@
 #include "macroscope.h"
 
 #include "psymtab.h"
+#include "parser-defs.h"
 
 /* Prototypes for local functions */
 
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 0d24cb5d0d3..d1cbef509b6 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -980,11 +980,11 @@ extern struct symbol *lookup_block_symbol (const struct block *, const char *,
 
 /* lookup a [struct, union, enum] by name, within a specified block.  */
 
-extern struct type *lookup_struct (const char *, struct block *);
+extern struct type *lookup_struct (const char *, const struct block *);
 
-extern struct type *lookup_union (const char *, struct block *);
+extern struct type *lookup_union (const char *, const struct block *);
 
-extern struct type *lookup_enum (const char *, struct block *);
+extern struct type *lookup_enum (const char *, const struct block *);
 
 /* from blockframe.c: */
 
diff --git a/gdb/valops.c b/gdb/valops.c
index 502fb0d1f07..1dd25799bfc 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -1516,7 +1516,7 @@ value_of_variable (struct symbol *var, const struct block *b)
 }
 
 struct value *
-address_of_variable (struct symbol *var, struct block *b)
+address_of_variable (struct symbol *var, const struct block *b)
 {
   struct type *type = SYMBOL_TYPE (var);
   struct value *val;
diff --git a/gdb/value.h b/gdb/value.h
index 36859357493..7a237153517 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -557,7 +557,8 @@ extern CORE_ADDR address_from_register (struct type *type, int regnum,
 extern struct value *value_of_variable (struct symbol *var,
 					const struct block *b);
 
-extern struct value *address_of_variable (struct symbol *var, struct block *b);
+extern struct value *address_of_variable (struct symbol *var,
+					  const struct block *b);
 
 extern struct value *value_of_register (int regnum, struct frame_info *frame);
 
diff --git a/gdb/varobj.c b/gdb/varobj.c
index 669969961eb..130f438f2d7 100644
--- a/gdb/varobj.c
+++ b/gdb/varobj.c
@@ -84,7 +84,7 @@ struct varobj_root
   struct expression *exp;
 
   /* Block for which this expression is valid.  */
-  struct block *valid_block;
+  const struct block *valid_block;
 
   /* The frame for this expression.  This field is set iff valid_block is
      not NULL.  */