DWARF: handle non-local references in nested functions

GDB's current behavior when dealing with non-local references in the
context of nested fuctions is approximative:

  - code using valops.c:value_of_variable read the first available stack
    frame that holds the corresponding variable (whereas there can be
    multiple candidates for this);

  - code directly relying on read_var_value will instead read non-local
    variables in frames where they are not even defined.

This change adds the necessary context to symbol reads (to get the block
they belong to) and to blocks (the static link property, if any) so that
GDB can make the proper decisions when dealing with non-local varibale
references.

gdb/ChangeLog:

	* ada-lang.c (ada_read_var_value): Add a var_block argument
	and pass it to default_read_var_value.
	* block.c (block_static_link): New accessor.
	* block.h (block_static_link): Declare it.
	* buildsym.c (finish_block_internal): Add a static_link
	argument.  If there is a static link, associate it to the new
	block.
	(finish_block): Add a static link argument and pass it to
	finish_block_internal.
	(end_symtab_get_static_block): Update calls to finish_block and
	to finish_block_internal.
	(end_symtab_with_blockvector): Update call to
	finish_block_internal.
	* buildsym.h: Forward-declare struct dynamic_prop.
	(struct context_stack): Add a static_link field.
	(finish_block): Add a static link argument.
	* c-exp.y: Remove an obsolete comment (evaluation of variables
	already start from the selected frame, and now they climb *up*
	the call stack) and propagate the block information to the
	produced expression.
	* d-exp.y: Likewise.
	* f-exp.y: Likewise.
	* go-exp.y: Likewise.
	* jv-exp.y: Likewise.
	* m2-exp.y: Likewise.
	* p-exp.y: Likewise.
	* coffread.c (coff_symtab_read): Update calls to finish_block.
	* dbxread.c (process_one_symbol): Likewise.
	* xcoffread.c (read_xcoff_symtab): Likewise.
	* compile/compile-c-symbols.c (convert_one_symbol): Promote the
	"sym" parameter to struct block_symbol, update its uses and pass
	its block to calls to read_var_value.
	(convert_symbol_sym): Update the calls to convert_one_symbol.
	* compile/compile-loc2c.c (do_compile_dwarf_expr_to_c): Update
	call to read_var_value.
	* dwarf2loc.c (block_op_get_frame_base): New.
	(dwarf2_block_frame_base_locexpr_funcs): Implement the
	get_frame_base method.
	(dwarf2_block_frame_base_loclist_funcs): Likewise.
	(dwarf2locexpr_baton_eval): Add a frame argument and use it
	instead of the selected frame in order to evaluate the
	expression.
	(dwarf2_evaluate_property): Add a frame argument.  Update call
	to dwarf2_locexpr_baton_eval to provide a frame in available and
	to handle the absence of address stack.
	* dwarf2loc.h (dwarf2_evaluate_property): Add a frame argument.
	* dwarf2read.c (attr_to_dynamic_prop): Add a forward
	declaration.
	(read_func_scope): Record any available static link description.
	Update call to finish_block.
	(read_lexical_block_scope): Update call to finish_block.
	* findvar.c (follow_static_link): New.
	(get_hosting_frame): New.
	(default_read_var_value): Add a var_block argument.  Use
	get_hosting_frame to handle non-local references.
	(read_var_value): Add a var_block argument and pass it to the
	LA_READ_VAR_VALUE method.
	* gdbtypes.c (resolve_dynamic_range): Update calls to
	dwarf2_evaluate_property.
	(resolve_dynamic_type_internal): Likewise.
	* guile/scm-frame.c (gdbscm_frame_read_var): Update call to
	read_var_value, passing it the block coming from symbol lookup.
	* guile/scm-symbol.c (gdbscm_symbol_value): Update call to
	read_var_value (TODO).
	* infcmd.c (finish_command_continuation): Update call to
	read_var_value, passing it the block coming from symbol lookup.
	* infrun.c (insert_exception_resume_breakpoint): Likewise.
	* language.h (struct language_defn): Add a var_block argument to
	the LA_READ_VAR_VALUE method.
	* objfiles.c (struct static_link_htab_entry): New.
	(static_link_htab_entry_hash): New.
	(static_link_htab_entry_eq): New.
	(objfile_register_static_link): New.
	(objfile_lookup_static_link): New.
	(free_objfile): Free the STATIC_LINKS hashed map if needed.
	* objfiles.h: Include hashtab.h.
	(struct objfile): Add a static_links field.
	(objfile_register_static_link): New.
	(objfile_lookup_static_link): New.
	* printcmd.c (print_variable_and_value): Update call to
	read_var_value.
	* python/py-finishbreakpoint.c (bpfinishpy_init): Likewise.
	* python/py-frame.c (frapy_read_var): Update call to
	read_var_value, passing it the block coming from symbol lookup.
	* python/py-framefilter.c (extract_sym): Add a sym_block
	parameter and set the pointed value to NULL (TODO).
	(enumerate_args): Update call to extract_sym.
	(enumerate_locals): Update calls to extract_sym and to
	read_var_value.
	* python/py-symbol.c (sympy_value): Update call to
	read_var_value (TODO).
	* stack.c (read_frame_local): Update call to read_var_value.
	(read_frame_arg): Likewise.
	(return_command): Likewise.
	* symtab.h (struct symbol_block_ops): Add a get_frame_base
	method.
	(struct symbol): Add a block field.
	(SYMBOL_BLOCK): New accessor.
	* valops.c (value_of_variable): Remove frame/block handling and
	pass the block argument to read_var_value, which does this job
	now.
	(value_struct_elt_for_reference): Update calls to
	read_var_value.
	(value_of_this): Pass the block found to read_var_value.
	* value.h (read_var_value): Add a var_block argument.
	(default_read_var_value): Likewise.

gdb/testsuite/ChangeLog:

	* gdb.base/nested-subp1.exp: New file.
	* gdb.base/nested-subp1.c: New file.
	* gdb.base/nested-subp2.exp: New file.
	* gdb.base/nested-subp2.c: New file.
	* gdb.base/nested-subp3.exp: New file.
	* gdb.base/nested-subp3.c: New file.

4 files changed, 31 insertions, 15 deletions

diff --git a/gdb/python/py-finishbreakpoint.c b/gdb/python/py-finishbreakpoint.c
index e543bb3..351f68c 100644
--- a/gdb/python/py-finishbreakpoint.c
+++ b/gdb/python/py-finishbreakpoint.c
@@ -265,7 +265,7 @@ bpfinishpy_init (PyObject *self, PyObject *args, PyObject *kwargs)
                   /* Ignore Python errors at this stage.  */
                   self_bpfinish->return_type = type_to_type_object (ret_type);
                   PyErr_Clear ();
-                  func_value = read_var_value (function, frame);
+                  func_value = read_var_value (function, NULL, frame);
                   self_bpfinish->function_value =
                       value_to_value_object (func_value);
                   PyErr_Clear ();
diff --git a/gdb/python/py-frame.c b/gdb/python/py-frame.c
index 7e5dd17..b448686 100644
--- a/gdb/python/py-frame.c
+++ b/gdb/python/py-frame.c
@@ -504,6 +504,7 @@ frapy_read_var (PyObject *self, PyObject *args)
   struct frame_info *frame;
   PyObject *sym_obj, *block_obj = NULL;
   struct symbol *var = NULL;	/* gcc-4.3.2 false warning.  */
+  const struct block *block = NULL;
   struct value *val = NULL;
 
   if (!PyArg_ParseTuple (args, "O|O", &sym_obj, &block_obj))
@@ -514,7 +515,6 @@ frapy_read_var (PyObject *self, PyObject *args)
   else if (gdbpy_is_string (sym_obj))
     {
       char *var_name;
-      const struct block *block = NULL;
       struct cleanup *cleanup;
 
       var_name = python_string_to_target_string (sym_obj);
@@ -536,11 +536,14 @@ frapy_read_var (PyObject *self, PyObject *args)
 
       TRY
 	{
+	  struct block_symbol lookup_sym;
 	  FRAPY_REQUIRE_VALID (self, frame);
 
 	  if (!block)
 	    block = get_frame_block (frame, NULL);
-	  var = lookup_symbol (var_name, block, VAR_DOMAIN, NULL).symbol;
+	  lookup_sym = lookup_symbol (var_name, block, VAR_DOMAIN, NULL);
+	  var = lookup_sym.symbol;
+	  block = lookup_sym.block;
 	}
       CATCH (except, RETURN_MASK_ALL)
 	{
@@ -572,7 +575,7 @@ frapy_read_var (PyObject *self, PyObject *args)
     {
       FRAPY_REQUIRE_VALID (self, frame);
 
-      val = read_var_value (var, frame);
+      val = read_var_value (var, block, frame);
     }
   CATCH (except, RETURN_MASK_ALL)
     {
diff --git a/gdb/python/py-framefilter.c b/gdb/python/py-framefilter.c
index e3336b1..ac97723 100644
--- a/gdb/python/py-framefilter.c
+++ b/gdb/python/py-framefilter.c
@@ -43,16 +43,17 @@ enum mi_print_types
    NAME is a  pass-through argument where the name of  the symbol will
    be written.  NAME is allocated in  this function, but the caller is
    responsible for clean up.  SYM is a pass-through argument where the
-   symbol will be written.  In the case of the API returning a string,
-   this will be set to NULL.  LANGUAGE is also a pass-through argument
-   denoting the language attributed to the Symbol.  In the case of SYM
-   being  NULL, this  will be  set to  the current  language.  Returns
-   EXT_LANG_BT_ERROR on error with the appropriate Python exception set, and
-   EXT_LANG_BT_OK on success.  */
+   symbol will be written and  SYM_BLOCK is a pass-through argument to
+   write  the block where the symbol lies in.  In the case of the  API
+   returning a  string,  this will be set to NULL.  LANGUAGE is also a
+   pass-through  argument  denoting  the  language  attributed  to the
+   Symbol.  In the case of SYM being  NULL, this  will be  set to  the
+   current  language.  Returns  EXT_LANG_BT_ERROR  on  error  with the
+   appropriate Python exception set, and EXT_LANG_BT_OK on success.  */
 
 static enum ext_lang_bt_status
 extract_sym (PyObject *obj, char **name, struct symbol **sym,
-	     const struct language_defn **language)
+	     struct block **sym_block, const struct language_defn **language)
 {
   PyObject *result = PyObject_CallMethod (obj, "symbol", NULL);
 
@@ -75,12 +76,18 @@ extract_sym (PyObject *obj, char **name, struct symbol **sym,
 	python_language.  */
       *language = python_language;
       *sym = NULL;
+      *sym_block = NULL;
     }
   else
     {
       /* This type checks 'result' during the conversion so we
 	 just call it unconditionally and check the return.  */
       *sym = symbol_object_to_symbol (result);
+      /* TODO: currently, we have no way to recover the block in which SYMBOL
+	 was found, so we have no block to return.  Trying to evaluate SYMBOL
+	 will yield an incorrect value when it's located in a FRAME and
+	 evaluated from another frame (as permitted in nested functions).  */
+      *sym_block = NULL;
 
       Py_DECREF (result);
 
@@ -537,10 +544,11 @@ enumerate_args (PyObject *iter,
       const struct language_defn *language;
       char *sym_name;
       struct symbol *sym;
+      struct block *sym_block;
       struct value *val;
       enum ext_lang_bt_status success = EXT_LANG_BT_ERROR;
 
-      success = extract_sym (item, &sym_name, &sym, &language);
+      success = extract_sym (item, &sym_name, &sym, &sym_block, &language);
       if (success == EXT_LANG_BT_ERROR)
 	{
 	  Py_DECREF (item);
@@ -736,12 +744,13 @@ enumerate_locals (PyObject *iter,
       struct value *val;
       enum ext_lang_bt_status success = EXT_LANG_BT_ERROR;
       struct symbol *sym;
+      struct block *sym_block;
       int local_indent = 8 + (8 * indent);
       struct cleanup *locals_cleanups;
 
       locals_cleanups = make_cleanup_py_decref (item);
 
-      success = extract_sym (item, &sym_name, &sym, &language);
+      success = extract_sym (item, &sym_name, &sym, &sym_block, &language);
       if (success == EXT_LANG_BT_ERROR)
 	{
 	  do_cleanups (locals_cleanups);
@@ -769,7 +778,7 @@ enumerate_locals (PyObject *iter,
 	{
 	  TRY
 	    {
-	      val = read_var_value (sym, frame);
+	      val = read_var_value (sym, sym_block, frame);
 	    }
 	  CATCH (except, RETURN_MASK_ERROR)
 	    {
diff --git a/gdb/python/py-symbol.c b/gdb/python/py-symbol.c
index f6466bd..3d2fa91 100644
--- a/gdb/python/py-symbol.c
+++ b/gdb/python/py-symbol.c
@@ -278,7 +278,11 @@ sympy_value (PyObject *self, PyObject *args)
       if (symbol_read_needs_frame (symbol) && frame_info == NULL)
 	error (_("symbol requires a frame to compute its value"));
 
-      value = read_var_value (symbol, frame_info);
+      /* TODO: currently, we have no way to recover the block in which SYMBOL
+	 was found, so we have no block to pass to read_var_value.  This will
+	 yield an incorrect value when symbol is not local to FRAME_INFO (this
+	 can happen with nested functions).  */
+      value = read_var_value (symbol, NULL, frame_info);
     }
   CATCH (except, RETURN_MASK_ALL)
     {