Re: [0/2] Inspect extra signal information

[Pedro Alves <pedro@codesourcery.com>]

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On Monday 12 January 2009 18:46:51, Pedro Alves wrote:
> 
> part 1:
> 
>  - Adds some infrastracture to be able to register reader and writer
>    functions that are responsible for reading and writing
>    a ``struct value'''s value.  We called those lval_computed values.  We've
>    been using these kinds of values for other things in our tree for a
>    couple of years already --- I've piggy-backed on that, so I got to
>    push it.  :-)
> 
>    This first patch applies on top of this other one:
> 
>    http://sourceware.org/ml/gdb-patches/2009-01/msg00252.html
> 

-- 
Pedro Alves

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2009-01-12  Jim Blandy  <jimb@codesourcery.com>
	    Daniel Jacobowitz  <dan@codesourcery.com>
	    Vladimir Prus  <vladimir@codesourcery.com>
	    Pedro Alves  <pedro@codesourcery.com>

	* defs.h (enum lval_type): New value: lval_computed.
	* value.h (struct lval_funcs): New type.
	(allocate_computed_value, value_computed_funcs)
	(value_computed_closure): New declarations.
	* value.c (struct value): Add a structure to the location union
	for computed lvalues, containing 'funcs' and 'closure' members.
	(allocate_computed_value, value_computed_funcs)
	(value_computed_closure): New functions.
	(value_free): For computed lvalues, call the closure's
	'free_closure' function before freeing the value itself.
	(value_copy): If we're copying an lval_computed value, call the
	closure's 'copy_closure' function.
	(set_value_component_location): If the original value is a
	computed lvalue, then call the closure's 'copy_closure' function.
	(value_of_internalvar): If an internal variable's value is a
	computed lvalue, make retrieving its value produce an equivalent
	computed lvalue.
	* valops.c (value_fetch_lazy): Unlazy computed lvalues by calling
	their read function.
	(value_assign): Assign to computed lvalues by calling their write
	function.

---
 gdb/defs.h   |    5 ++-
 gdb/valops.c |   12 +++++++-
 gdb/value.c  |   85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 gdb/value.h  |   54 +++++++++++++++++++++++++++++++++++++
 4 files changed, 151 insertions(+), 5 deletions(-)

Index: gdb/defs.h
===================================================================
--- gdb/defs.h.orig	2009-01-11 15:40:11.000000000 +0000
+++ gdb/defs.h	2009-01-12 16:29:28.000000000 +0000
@@ -652,7 +652,10 @@ enum lval_type
     /* In a gdb internal variable.  */
     lval_internalvar,
     /* Part of a gdb internal variable (structure field).  */
-    lval_internalvar_component
+    lval_internalvar_component,
+    /* Value's bits are fetched and stored using functions provided by
+       its creator.  */
+    lval_computed
   };
 
 /* Control types for commands */
Index: gdb/value.h
===================================================================
--- gdb/value.h.orig	2009-01-12 12:40:32.000000000 +0000
+++ gdb/value.h	2009-01-12 16:48:53.000000000 +0000
@@ -142,6 +142,60 @@ extern void set_value_pointed_to_offset 
 extern int value_embedded_offset (struct value *value);
 extern void set_value_embedded_offset (struct value *value, int val);
 
+/* For lval_computed values, this structure holds functions used to
+   retrieve and set the value (or portions of the value).
+
+   For each function, 'V' is the 'this' pointer: an lval_funcs
+   function F may always assume that the V it receives is an
+   lval_computed value, and has F in the appropriate slot of its
+   lval_funcs structure.  */
+
+struct lval_funcs
+{
+  /* Fill in VALUE's contents.  This is used to "un-lazy" values.  If
+     a problem arises in obtaining VALUE's bits, this function should
+     call 'error'.  */
+  void (*read) (struct value *v);
+
+  /* Handle an assignment TOVAL = FROMVAL by writing the value of
+     FROMVAL to TOVAL's location.  The contents of TOVAL have not yet
+     been updated.  If a problem arises in doing so, this function
+     should call 'error'.  */
+  void (*write) (struct value *toval, struct value *fromval);
+
+  /* Return a duplicate of VALUE's closure, for use in a new value.
+     This may simply return the same closure, if VALUE's is
+     reference-counted or statically allocated.
+
+     This may be NULL, in which case VALUE's closure is re-used in the
+     new value.  */
+  void *(*copy_closure) (struct value *v);
+
+  /* Drop VALUE's reference to its closure.  Maybe this frees the
+     closure; maybe this decrements a reference count; maybe the
+     closure is statically allocated and this does nothing.
+
+     This may be NULL, in which case no action is taken to free
+     VALUE's closure.  */
+  void (*free_closure) (struct value *v);
+};
+
+/* Create a computed lvalue, with type TYPE, function pointers FUNCS,
+   and closure CLOSURE.  */
+
+extern struct value *allocate_computed_value (struct type *type,
+                                              struct lval_funcs *funcs,
+                                              void *closure);
+
+/* If VALUE is lval_computed, return its lval_funcs structure.  */
+
+extern struct lval_funcs *value_computed_funcs (struct value *value);
+
+/* If VALUE is lval_computed, return its closure.  The meaning of the
+   returned value depends on the functions VALUE uses.  */
+
+extern void *value_computed_closure (struct value *value);
+
 /* If zero, contents of this value are in the contents field.  If
    nonzero, contents are in inferior.  If the lval field is lval_memory,
    the contents are in inferior memory at location.address plus offset.
Index: gdb/value.c
===================================================================
--- gdb/value.c.orig	2009-01-12 11:25:23.000000000 +0000
+++ gdb/value.c	2009-01-12 16:48:54.000000000 +0000
@@ -63,6 +63,15 @@ struct value
 
     /* Pointer to internal variable.  */
     struct internalvar *internalvar;
+
+    /* If lval == lval_computed, this is a set of function pointers
+       to use to access and describe the value, and a closure pointer
+       for them to use.  */
+    struct
+    {
+      struct lval_funcs *funcs; /* Functions to call.  */
+      void *closure;            /* Closure for those functions to use.  */
+    } computed;
   } location;
 
   /* Describes offset of a value within lval of a structure in bytes.
@@ -296,6 +305,20 @@ value_remove_from_list (struct value **h
       }
 }
 
+struct value *
+allocate_computed_value (struct type *type,
+                         struct lval_funcs *funcs,
+                         void *closure)
+{
+  struct value *v = allocate_value (type);
+  VALUE_LVAL (v) = lval_computed;
+  v->location.computed.funcs = funcs;
+  v->location.computed.closure = closure;
+  set_value_lazy (v, 1);
+
+  return v;
+}
+
 /* Accessor methods.  */
 
 struct value *
@@ -458,6 +481,22 @@ set_value_pointed_to_offset (struct valu
   value->pointed_to_offset = val;
 }
 
+struct lval_funcs *
+value_computed_funcs (struct value *v)
+{
+  gdb_assert (VALUE_LVAL (v) == lval_computed);
+
+  return v->location.computed.funcs;
+}
+
+void *
+value_computed_closure (struct value *v)
+{
+  gdb_assert (VALUE_LVAL (v) == lval_computed);
+
+  return v->location.computed.closure;
+}
+
 enum lval_type *
 deprecated_value_lval_hack (struct value *value)
 {
@@ -512,7 +551,17 @@ void
 value_free (struct value *val)
 {
   if (val)
-    xfree (val->contents);
+    {
+      if (VALUE_LVAL (val) == lval_computed)
+	{
+	  struct lval_funcs *funcs = val->location.computed.funcs;
+
+	  if (funcs->free_closure)
+	    funcs->free_closure (val);
+	}
+
+      xfree (val->contents);
+    }
   xfree (val);
 }
 
@@ -625,6 +674,13 @@ value_copy (struct value *arg)
 	      TYPE_LENGTH (value_enclosing_type (arg)));
 
     }
+  if (VALUE_LVAL (val) == lval_computed)
+    {
+      struct lval_funcs *funcs = val->location.computed.funcs;
+
+      if (funcs->copy_closure)
+        val->location.computed.closure = funcs->copy_closure (val);
+    }
   return val;
 }
 
@@ -635,7 +691,15 @@ set_value_component_location (struct val
     VALUE_LVAL (component) = lval_internalvar_component;
   else
     VALUE_LVAL (component) = VALUE_LVAL (whole);
+
   component->location = whole->location;
+  if (VALUE_LVAL (whole) == lval_computed)
+    {
+      struct lval_funcs *funcs = whole->location.computed.funcs;
+
+      if (funcs->copy_closure)
+        component->location.computed.closure = funcs->copy_closure (whole);
+    }
 }
 
 \f
@@ -872,8 +936,23 @@ value_of_internalvar (struct internalvar
   val = value_copy (var->value);
   if (value_lazy (val))
     value_fetch_lazy (val);
-  VALUE_LVAL (val) = lval_internalvar;
-  VALUE_INTERNALVAR (val) = var;
+
+  /* If the variable's value is a computed lvalue, we want references
+     to it to produce another computed lvalue, where referencces and
+     assignments actually operate through the computed value's
+     functions.
+
+     This means that internal variables with computed values behave a
+     little differently from other internal variables: assignments to
+     them don't just replace the previous value altogether.  At the
+     moment, this seems like the behavior we want.  */
+  if (var->value->lval == lval_computed)
+    VALUE_LVAL (val) = lval_computed;
+  else
+    {
+      VALUE_LVAL (val) = lval_internalvar;
+      VALUE_INTERNALVAR (val) = var;
+    }
 
   /* Values are always stored in the target's byte order.  When connected to a
      target this will most likely always be correct, so there's normally no
Index: gdb/valops.c
===================================================================
--- gdb/valops.c.orig	2009-01-12 11:25:23.000000000 +0000
+++ gdb/valops.c	2009-01-12 14:21:01.000000000 +0000
@@ -727,6 +727,8 @@ value_fetch_lazy (struct value *val)
 	 watchpoints from trying to watch the saved frame pointer.  */
       value_free_to_mark (mark);
     }
+  else if (VALUE_LVAL (val) == lval_computed)
+    value_computed_funcs (val)->read (val);
   else
     internal_error (__FILE__, __LINE__, "Unexpected lazy value type.");
 
@@ -895,7 +897,15 @@ value_assign (struct value *toval, struc
 	observer_notify_target_changed (&current_target);
 	break;
       }
-      
+
+    case lval_computed:
+      {
+	struct lval_funcs *funcs = value_computed_funcs (toval);
+
+	funcs->write (toval, fromval);
+      }
+      break;
+
     default:
       error (_("Left operand of assignment is not an lvalue."));
     }