language-specific read_var_value for Ada renamings

The purpose of this patch is to better support renamings in the
"info locals" command. Consider ...

    procedure Foo is
       GV : Integer renames Pck.Global_Variable;
    begin
       Increment (GV); -- STOP
    end Foo;

... Pck.Global_Variable is just an integer. After having stopped at
the "STOP" line, "info locals" yields:

    (gdb) info locals
    gv = <error reading variable gv (Cannot access memory at address 0xffffffffffffffff)>

In reality, two things are happening:

   (1) Variable "GV" does not exist, which is normal, since there is
       "GV" the renaming of another variable;

   (2) But to allow the user access to that renaming the same way
       the code has, the compiler produces an artificial variable
       whose name encodes the renaming:

        gv___XR_pck__global_variable___XE

       For practical reasons, the artificial variable itself is given
       irrelevant types and addresses.

But the "info locals" command does not act as if it was a short-cut
of "foreach VAR in locals, print VAR". Instead it gets the value of
each VAR directly, which does not work in this case, since the variable
is artificial and needs to be decoded first.

This patch makes the "read_var_value" routine language-specific.
The old implementation of "read_var_value" gets renamed to
"default_read_var_value" and all languages now use it (unchanged
behavior), except for Ada. In Ada, the new function ada_read_var_value
checks if we have a renaming, and if so, evaluates its value, or else
defers to default_read_var_value.

gdb/ChangeLog:

        * language.h (struct language_defn): New "method" la_read_var_value.
        * findvar.c: #include "language.h".
        (default_read_var_value): Renames read_var_value.  Rewrite
        function description.
        (read_var_value): New function.
        * value.h (default_read_var_value): Add prototype.
        * ada-lang.c (ada_read_renaming_var_value, ada_read_var_value):
        New functions.
        (ada_language_defn): Add entry for la_read_var_value.
        * c-lang.c, d-lang.c, f-lang.c, jv-lang.c, language.c,
        * m2-lang.c, objc-lang.c, opencl-lang.c, p-lang.c: Update
        language_defn structures to add entry for new la_read_var_value
        field.

14 files changed, 105 insertions, 6 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 41d0277..a26e694 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,19 @@
+2012-03-02  Joel Brobecker  <brobecker@adacore.com>
+
+	* language.h (struct language_defn): New "method" la_read_var_value.
+	* findvar.c: #include "language.h".
+	(default_read_var_value): Renames read_var_value.  Rewrite
+	function description.
+	(read_var_value): New function.
+	* value.h (default_read_var_value): Add prototype.
+	* ada-lang.c (ada_read_renaming_var_value, ada_read_var_value):
+	New functions.
+	(ada_language_defn): Add entry for la_read_var_value.
+	* c-lang.c, d-lang.c, f-lang.c, jv-lang.c, language.c,
+	* m2-lang.c, objc-lang.c, opencl-lang.c, p-lang.c: Update
+	language_defn structures to add entry for new la_read_var_value
+	field.
+
 2012-03-02  Tom Tromey  <tromey@redhat.com>
 	    Pedro Alves  <palves@redhat.com>
 
diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 4c17eaa..040d606 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -4041,8 +4041,30 @@ parse_old_style_renaming (struct type *type,
   if (len != NULL)
     *len = suffix - info;
   return kind;
-}  
+}
+
+/* Compute the value of the given RENAMING_SYM, which is expected to
+   be a symbol encoding a renaming expression.  BLOCK is the block
+   used to evaluate the renaming.  */
 
+static struct value *
+ada_read_renaming_var_value (struct symbol *renaming_sym,
+			     struct block *block)
+{
+  char *sym_name;
+  struct expression *expr;
+  struct value *value;
+  struct cleanup *old_chain = NULL;
+
+  sym_name = xstrdup (SYMBOL_LINKAGE_NAME (renaming_sym));
+  old_chain = make_cleanup (xfree, sym_name);
+  expr = parse_exp_1 (&sym_name, block, 0);
+  make_cleanup (free_current_contents, &expr);
+  value = evaluate_expression (expr);
+
+  do_cleanups (old_chain);
+  return value;
+}
 
 
                                 /* Evaluation: Function Calls */
@@ -12437,6 +12459,28 @@ ada_get_symbol_name_cmp (const char *lookup_name)
     return compare_names;
 }
 
+/* Implement the "la_read_var_value" language_defn method for Ada.  */
+
+static struct value *
+ada_read_var_value (struct symbol *var, struct frame_info *frame)
+{
+  struct block *frame_block = NULL;
+  struct symbol *renaming_sym = NULL;
+
+  /* The only case where default_read_var_value is not sufficient
+     is when VAR is a renaming...  */
+  if (frame)
+    frame_block = get_frame_block (frame, NULL);
+  if (frame_block)
+    renaming_sym = ada_find_renaming_symbol (var, frame_block);
+  if (renaming_sym != NULL)
+    return ada_read_renaming_var_value (renaming_sym, frame_block);
+
+  /* This is a typical case where we expect the default_read_var_value
+     function to work.  */
+  return default_read_var_value (var, frame);
+}
+
 const struct language_defn ada_language_defn = {
   "ada",                        /* Language name */
   language_ada,
@@ -12457,6 +12501,7 @@ const struct language_defn ada_language_defn = {
   ada_print_typedef,            /* Print a typedef using appropriate syntax */
   ada_val_print,                /* Print a value using appropriate syntax */
   ada_value_print,              /* Print a top-level value */
+  ada_read_var_value,		/* la_read_var_value */
   NULL,                         /* Language specific skip_trampoline */
   NULL,                         /* name_of_this */
   ada_lookup_symbol_nonlocal,   /* Looking up non-local symbols.  */
diff --git a/gdb/c-lang.c b/gdb/c-lang.c
index 767d13a..28dce8d 100644
--- a/gdb/c-lang.c
+++ b/gdb/c-lang.c
@@ -847,6 +847,7 @@ const struct language_defn c_language_defn =
   c_print_typedef,		/* Print a typedef using appropriate syntax */
   c_val_print,			/* Print a value using appropriate syntax */
   c_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,				/* name_of_this */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
@@ -970,6 +971,7 @@ const struct language_defn cplus_language_defn =
   c_print_typedef,		/* Print a typedef using appropriate syntax */
   c_val_print,			/* Print a value using appropriate syntax */
   c_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   cplus_skip_trampoline,	/* Language specific skip_trampoline */
   "this",                       /* name_of_this */
   cp_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
@@ -1011,6 +1013,7 @@ const struct language_defn asm_language_defn =
   c_print_typedef,		/* Print a typedef using appropriate syntax */
   c_val_print,			/* Print a value using appropriate syntax */
   c_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,				/* name_of_this */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
@@ -1057,6 +1060,7 @@ const struct language_defn minimal_language_defn =
   c_print_typedef,		/* Print a typedef using appropriate syntax */
   c_val_print,			/* Print a value using appropriate syntax */
   c_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,				/* name_of_this */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
diff --git a/gdb/d-lang.c b/gdb/d-lang.c
index 202820e..9a8cf52 100644
--- a/gdb/d-lang.c
+++ b/gdb/d-lang.c
@@ -256,6 +256,7 @@ static const struct language_defn d_language_defn =
 				   syntax.  */
   d_val_print,			/* Print a value using appropriate syntax.  */
   c_value_print,		/* Print a top-level value.  */
+  default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline.  */
   "this",
   basic_lookup_symbol_nonlocal, 
diff --git a/gdb/f-lang.c b/gdb/f-lang.c
index ef78bc3..3368d01 100644
--- a/gdb/f-lang.c
+++ b/gdb/f-lang.c
@@ -289,6 +289,7 @@ const struct language_defn f_language_defn =
   default_print_typedef,	/* Print a typedef using appropriate syntax */
   f_val_print,			/* Print a value using appropriate syntax */
   c_value_print,		/* FIXME */
+  default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,                    	/* name_of_this */
   cp_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
diff --git a/gdb/findvar.c b/gdb/findvar.c
index 79c4221..9009e6f 100644
--- a/gdb/findvar.c
+++ b/gdb/findvar.c
@@ -34,6 +34,7 @@
 #include "user-regs.h"
 #include "block.h"
 #include "objfiles.h"
+#include "language.h"
 
 /* Basic byte-swapping routines.  All 'extract' functions return a
    host-format integer from a target-format integer at ADDR which is
@@ -405,13 +406,11 @@ symbol_read_needs_frame (struct symbol *sym)
   return 1;
 }
 
-/* Given a struct symbol for a variable,
-   and a stack frame id, read the value of the variable
-   and return a (pointer to a) struct value containing the value.
-   If the variable cannot be found, throw error.  */
+/* A default implementation for the "la_read_var_value" hook in
+   the language vector which should work in most situations.  */
 
 struct value *
-read_var_value (struct symbol *var, struct frame_info *frame)
+default_read_var_value (struct symbol *var, struct frame_info *frame)
 {
   struct value *v;
   struct type *type = SYMBOL_TYPE (var);
@@ -594,6 +593,19 @@ read_var_value (struct symbol *var, struct frame_info *frame)
   return v;
 }
 
+/* Calls VAR's language la_read_var_value hook with the given arguments.  */
+
+struct value *
+read_var_value (struct symbol *var, struct frame_info *frame)
+{
+  const struct language_defn *lang = language_def (SYMBOL_LANGUAGE (var));
+
+  gdb_assert (lang != NULL);
+  gdb_assert (lang->la_read_var_value != NULL);
+
+  return lang->la_read_var_value (var, frame);
+}
+
 /* Install default attributes for register values.  */
 
 struct value *
diff --git a/gdb/jv-lang.c b/gdb/jv-lang.c
index 18a7c19..08ecf5f 100644
--- a/gdb/jv-lang.c
+++ b/gdb/jv-lang.c
@@ -1181,6 +1181,7 @@ const struct language_defn java_language_defn =
   default_print_typedef,	/* Print a typedef using appropriate syntax */
   java_val_print,		/* Print a value using appropriate syntax */
   java_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   "this",	                /* name_of_this */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
diff --git a/gdb/language.c b/gdb/language.c
index ae34108..f0a8697 100644
--- a/gdb/language.c
+++ b/gdb/language.c
@@ -917,6 +917,7 @@ const struct language_defn unknown_language_defn =
   default_print_typedef,	/* Print a typedef using appropriate syntax */
   unk_lang_val_print,		/* Print a value using appropriate syntax */
   unk_lang_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   unk_lang_trampoline,		/* Language specific skip_trampoline */
   "this",        	    	/* name_of_this */
   basic_lookup_symbol_nonlocal, /* lookup_symbol_nonlocal */
@@ -960,6 +961,7 @@ const struct language_defn auto_language_defn =
   default_print_typedef,	/* Print a typedef using appropriate syntax */
   unk_lang_val_print,		/* Print a value using appropriate syntax */
   unk_lang_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   unk_lang_trampoline,		/* Language specific skip_trampoline */
   "this",		        /* name_of_this */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
@@ -1001,6 +1003,7 @@ const struct language_defn local_language_defn =
   default_print_typedef,	/* Print a typedef using appropriate syntax */
   unk_lang_val_print,		/* Print a value using appropriate syntax */
   unk_lang_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   unk_lang_trampoline,		/* Language specific skip_trampoline */
   "this", 		        /* name_of_this */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
diff --git a/gdb/language.h b/gdb/language.h
index 76dad32..d612c70 100644
--- a/gdb/language.h
+++ b/gdb/language.h
@@ -252,6 +252,15 @@ struct language_defn
     void (*la_value_print) (struct value *, struct ui_file *,
 			    const struct value_print_options *);
 
+    /* Given a symbol VAR, and a stack frame id FRAME, read the value
+       of the variable an return (pointer to a) struct value containing
+       the value.
+
+       Throw an error if the variable cannot be found.  */
+
+    struct value *(*la_read_var_value) (struct symbol *var,
+					struct frame_info *frame);
+
     /* PC is possibly an unknown languages trampoline.
        If that PC falls in a trampoline belonging to this language,
        return the address of the first pc in the real function, or 0
diff --git a/gdb/m2-lang.c b/gdb/m2-lang.c
index 9cd27c9..8faa6c1 100644
--- a/gdb/m2-lang.c
+++ b/gdb/m2-lang.c
@@ -385,6 +385,7 @@ const struct language_defn m2_language_defn =
   m2_print_typedef,		/* Print a typedef using appropriate syntax */
   m2_val_print,			/* Print a value using appropriate syntax */
   c_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,		                /* name_of_this */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
diff --git a/gdb/objc-lang.c b/gdb/objc-lang.c
index 74528c8..15bf792 100644
--- a/gdb/objc-lang.c
+++ b/gdb/objc-lang.c
@@ -524,6 +524,7 @@ const struct language_defn objc_language_defn = {
   c_print_typedef,		/* Print a typedef using appropriate syntax */
   c_val_print,			/* Print a value using appropriate syntax */
   c_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   objc_skip_trampoline, 	/* Language specific skip_trampoline */
   "self",		        /* name_of_this */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
diff --git a/gdb/opencl-lang.c b/gdb/opencl-lang.c
index 3554d18..54075a4 100644
--- a/gdb/opencl-lang.c
+++ b/gdb/opencl-lang.c
@@ -1008,6 +1008,7 @@ const struct language_defn opencl_language_defn =
   c_print_typedef,		/* Print a typedef using appropriate syntax */
   c_val_print,			/* Print a value using appropriate syntax */
   c_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   NULL,                         /* name_of_this */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
diff --git a/gdb/p-lang.c b/gdb/p-lang.c
index 826d24f..c59ba0b 100644
--- a/gdb/p-lang.c
+++ b/gdb/p-lang.c
@@ -444,6 +444,7 @@ const struct language_defn pascal_language_defn =
   pascal_print_typedef,		/* Print a typedef using appropriate syntax */
   pascal_val_print,		/* Print a value using appropriate syntax */
   pascal_value_print,		/* Print a top-level value */
+  default_read_var_value,	/* la_read_var_value */
   NULL,				/* Language specific skip_trampoline */
   "this",		        /* name_of_this */
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
diff --git a/gdb/value.h b/gdb/value.h
index f0fdb4c..3ce0f88 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -536,6 +536,9 @@ extern int symbol_read_needs_frame (struct symbol *);
 extern struct value *read_var_value (struct symbol *var,
 				     struct frame_info *frame);
 
+extern struct value *default_read_var_value (struct symbol *var,
+					     struct frame_info *frame);
+
 extern struct value *allocate_value (struct type *type);
 extern struct value *allocate_value_lazy (struct type *type);
 extern void allocate_value_contents (struct value *value);