Re: Frames as scopes

[Thiago Jung Bauermann <bauerman at br dot ibm dot com>]

El lun, 05-01-2009 a las 11:02 -0800, Jim Blandy escribiÃ:
> On Fri, Jan 2, 2009 at 6:14 PM, Thiago Jung Bauermann
> <bauerman@br.ibm.com> wrote:
> > El jue, 01-01-2009 a las 09:47 -0700, Doug Evans escribiÃ:
> >> On Tue, Dec 30, 2008 at 2:57 PM, Jim Blandy <jimb@red-bean.com> wrote:
> >> > Is there a way to look up a variable in the scope specified by a frame?  Saying
> >> >
> >> >    gdb.lookup_symbol('argc',gdb.block_for_pc(gdb.current_frame().pc()),gdb.SYMBOL_VAR_DOMAIN)
> >> >
> >> > seems circuitous; perhaps lookup_symbol could default the domain to
> >> > SYMBOL_VAR_DOMAIN, and accept a frame to indicate scope, defaulting to
> >> > the current frame.  Then one could simply say:
> >> >
> >> >    gdb.lookup_symbol('argc')
> >> >
> >> > and get what one expects.
> >
> > Default to current_frame or to selected_frame? I tend to prefer the
> > later, but I don't know which one would be better as a default. Apart
> > from that, I think the defaults you mention are a good idea.
> 
> You're right, selected_frame is better --- its whole reason for
> existence is to provide a default frame for things. :)

Ok, I committed the patch below which adds those defaults to lookup
symbol. Except that it continues expecting a Block object instead of a
Frame object. Since Frame now has a "block" method, it shouldn't be too
inconvenient. If no Block is provided, it gets one from selected_frame.

> Perhaps unfriendly primitives (implemented in C) would live in a
> separate module (gdb.primitives), and then friendly Python
> functions/classes based on them would live in the gdb module.  The
> latter would be the only documented, supported interface.

That was one basic choice we face at the beginning of the work: expose
crude functions from C to Python and use them to build a Python API
using some Python glue, or directly provide Python classes implemented
in C without the Python glue? We opted for the latter, though no strong
argument was uttered supporting either option... At least for now, I
don't see a problem with the approach we took.
-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center


2009-01-29  Thiago Jung Bauermann  <bauerman@br.ibm.com>

	* python/python-symbol.c (gdbpy_lookup_symbol): Turn block and domain
	into optional parameters.
	* python/lib/gdb/command/backtrace.py (write_symbol): Don't explicitly
	define domain in call to `gdb.lookup_symbol'.

diff --git a/gdb/python/lib/gdb/command/backtrace.py b/gdb/python/lib/gdb/command/backtrace.py
index 97c76d1..e01e2b6 100644
--- a/gdb/python/lib/gdb/command/backtrace.py
+++ b/gdb/python/lib/gdb/command/backtrace.py
@@ -27,7 +27,7 @@ class FrameWrapper:
 
     def write_symbol (self, stream, sym, block):
         if len (sym.linkage_name):
-            nsym, is_field_of_this = gdb.lookup_symbol (sym.linkage_name, block, gdb.SYMBOL_VAR_DOMAIN)
+            nsym, is_field_of_this = gdb.lookup_symbol (sym.linkage_name, block)
             if nsym.addr_class != gdb.SYMBOL_LOC_REGISTER:
                 sym = nsym
 
diff --git a/gdb/python/python-symbol.c b/gdb/python/python-symbol.c
index aaea04c..223e6d3 100644
--- a/gdb/python/python-symbol.c
+++ b/gdb/python/python-symbol.c
@@ -18,6 +18,9 @@
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include "defs.h"
+#include "block.h"
+#include "exceptions.h"
+#include "frame.h"
 #include "symtab.h"
 #include "python-internal.h"
 
@@ -170,21 +173,29 @@ symbol_object_to_symbol (PyObject *obj)
    is_a_field_of_this.  */
 PyObject *gdbpy_lookup_symbol (PyObject *self, PyObject *args)
 {
-  int domain, is_a_field_of_this = 0;
+  int domain = VAR_DOMAIN, is_a_field_of_this = 0;
   const char *name;
   struct symbol *symbol;
-  PyObject *block_obj, *ret_tuple, *sym_obj, *bool_obj;
-  struct block *block;
+  PyObject *block_obj = NULL, *ret_tuple, *sym_obj, *bool_obj;
+  struct block *block = NULL;
 
-  if (! PyArg_ParseTuple (args, "sO!i", &name, &block_object_type, &block_obj,
+  if (! PyArg_ParseTuple (args, "s|O!i", &name, &block_object_type, &block_obj,
 			  &domain))
     return NULL;
 
-  block = block_object_to_block (block_obj);
-  if (! block)
+  if (block_obj)
+    block = block_object_to_block (block_obj);
+  else
     {
-      PyErr_SetString (PyExc_RuntimeError, "second argument must be block");
-      return NULL;
+      struct frame_info *selected_frame;
+      volatile struct gdb_exception except;
+
+      TRY_CATCH (except, RETURN_MASK_ALL)
+	{
+	  selected_frame  = get_selected_frame (_("No frame selected."));
+	  block = block_for_pc (get_frame_address_in_block (selected_frame));
+	}
+      GDB_PY_HANDLE_EXCEPTION (except);
     }
 
   symbol = lookup_symbol (name, block, domain, &is_a_field_of_this);