Re: [RFC/Patch v4] Call overloaded operators to perform valid Python operations on struct/class values.

[Siva Chandra <sivachandra@google.com>]

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I have pushed the attached patch (which includes the corrections
suggested by Eli).

On Thu, Feb 6, 2014 at 10:53 PM, Doug Evans <dje@google.com> wrote:
> Hi.
>
> The patch is fine with me.
>
> I put in some time to play with the patch.
> One thing I wondered about is what happens if the user does string1 + string2?
> We do leak memory.  That's not a problem with this patch of course,
> though by making this scriptable the problem gets worse.
> I filed https://sourceware.org/bugzilla/show_bug.cgi?id=16537
>
> btw, Just writing this down since it's on my mind:
> If anything needs to be done it should be addressed in a separate
> patch.  And maybe leaving things as-is is ok, and just a doc addition
> is all that's needed. Anyways, hand called functions (which includes
> c++ operators) run the inferior (setting aside using debug methods).
> The more we make it easy to invoke c++ operators the more users are
> going to run into the issues of hand called functions (e.g. what if
> they have a breakpoint set that the c++ operator happens to trip?).

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diff --git a/gdb/NEWS b/gdb/NEWS
index b54a414..135858e 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -82,6 +82,12 @@ qXfer:btrace:read's annex
   The qXfer:btrace:read packet supports a new annex 'delta' to read
   branch trace incrementally.
 
+* Python Scripting
+
+  ** Valid Python operations on gdb.Value objects representing
+     structs/classes invoke the corresponding overloaded operators if
+     available.
+
 * New targets
 PowerPC64 GNU/Linux little-endian	powerpc64le-*-linux*
 
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index 62636a4..90b7074 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -528,7 +528,26 @@ bar = some_val + 2
 
 @noindent
 As result of this, @code{bar} will also be a @code{gdb.Value} object
-whose values are of the same type as those of @code{some_val}.
+whose values are of the same type as those of @code{some_val}.  Valid
+Python operations can also be performed on @code{gdb.Value} objects
+representing a @code{struct} or @code{class} object.  For such cases,
+the overloaded operator (if present), is used to perform the operation.
+For example, if @code{val1} and @code{val2} are @code{gdb.Value} objects
+representing instances of a @code{class} which overloads the @code{+}
+operator, then one can use the @code{+} operator in their Python script
+as follows:
+
+@smallexample
+val3 = val1 + val2
+@end smallexample
+
+@noindent
+The result of the operation @code{val3} is also a @code{gdb.Value}
+object corresponding to the value returned by the overloaded @code{+}
+operator.  In general, overloaded operators are invoked for the
+following operations: @code{+} (binary addition), @code{-} (binary
+subtraction), @code{*} (multiplication), @code{/}, @code{%}, @code{<<},
+@code{>>}, @code{|}, @code{&}, @code{^}.
 
 Inferior values that are structures or instances of some class can
 be accessed using the Python @dfn{dictionary syntax}.  For example, if
diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index f8a8a98..75aa642 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -933,6 +933,8 @@ valpy_binop (enum valpy_opcode opcode, PyObject *self, PyObject *other)
       struct value *arg1, *arg2;
       struct cleanup *cleanup = make_cleanup_value_free_to_mark (value_mark ());
       struct value *res_val = NULL;
+      enum exp_opcode op = OP_NULL;
+      int handled = 0;
 
       /* If the gdb.Value object is the second operand, then it will be passed
 	 to us as the OTHER argument, and SELF will be an entirely different
@@ -964,6 +966,7 @@ valpy_binop (enum valpy_opcode opcode, PyObject *self, PyObject *other)
 	    CHECK_TYPEDEF (rtype);
 	    rtype = STRIP_REFERENCE (rtype);
 
+	    handled = 1;
 	    if (TYPE_CODE (ltype) == TYPE_CODE_PTR
 		&& is_integral_type (rtype))
 	      res_val = value_ptradd (arg1, value_as_long (arg2));
@@ -971,7 +974,10 @@ valpy_binop (enum valpy_opcode opcode, PyObject *self, PyObject *other)
 		     && is_integral_type (ltype))
 	      res_val = value_ptradd (arg2, value_as_long (arg1));
 	    else
-	      res_val = value_binop (arg1, arg2, BINOP_ADD);
+	      {
+		handled = 0;
+		op = BINOP_ADD;
+	      }
 	  }
 	  break;
 	case VALPY_SUB:
@@ -984,6 +990,7 @@ valpy_binop (enum valpy_opcode opcode, PyObject *self, PyObject *other)
 	    CHECK_TYPEDEF (rtype);
 	    rtype = STRIP_REFERENCE (rtype);
 
+	    handled = 1;
 	    if (TYPE_CODE (ltype) == TYPE_CODE_PTR
 		&& TYPE_CODE (rtype) == TYPE_CODE_PTR)
 	      /* A ptrdiff_t for the target would be preferable here.  */
@@ -993,38 +1000,49 @@ valpy_binop (enum valpy_opcode opcode, PyObject *self, PyObject *other)
 		     && is_integral_type (rtype))
 	      res_val = value_ptradd (arg1, - value_as_long (arg2));
 	    else
-	      res_val = value_binop (arg1, arg2, BINOP_SUB);
+	      {
+		handled = 0;
+		op = BINOP_SUB;
+	      }
 	  }
 	  break;
 	case VALPY_MUL:
-	  res_val = value_binop (arg1, arg2, BINOP_MUL);
+	  op = BINOP_MUL;
 	  break;
 	case VALPY_DIV:
-	  res_val = value_binop (arg1, arg2, BINOP_DIV);
+	  op = BINOP_DIV;
 	  break;
 	case VALPY_REM:
-	  res_val = value_binop (arg1, arg2, BINOP_REM);
+	  op = BINOP_REM;
 	  break;
 	case VALPY_POW:
-	  res_val = value_binop (arg1, arg2, BINOP_EXP);
+	  op = BINOP_EXP;
 	  break;
 	case VALPY_LSH:
-	  res_val = value_binop (arg1, arg2, BINOP_LSH);
+	  op = BINOP_LSH;
 	  break;
 	case VALPY_RSH:
-	  res_val = value_binop (arg1, arg2, BINOP_RSH);
+	  op = BINOP_RSH;
 	  break;
 	case VALPY_BITAND:
-	  res_val = value_binop (arg1, arg2, BINOP_BITWISE_AND);
+	  op = BINOP_BITWISE_AND;
 	  break;
 	case VALPY_BITOR:
-	  res_val = value_binop (arg1, arg2, BINOP_BITWISE_IOR);
+	  op = BINOP_BITWISE_IOR;
 	  break;
 	case VALPY_BITXOR:
-	  res_val = value_binop (arg1, arg2, BINOP_BITWISE_XOR);
+	  op = BINOP_BITWISE_XOR;
 	  break;
 	}
 
+      if (!handled)
+	{
+	  if (binop_user_defined_p (op, arg1, arg2))
+	    res_val = value_x_binop (arg1, arg2, op, OP_NULL, EVAL_NORMAL);
+	  else
+	    res_val = value_binop (arg1, arg2, op);
+	}
+
       if (res_val)
 	result = value_to_value_object (res_val);
 
diff --git a/gdb/testsuite/gdb.python/py-value-cc.cc b/gdb/testsuite/gdb.python/py-value-cc.cc
index ace957a..7ea4f5d 100644
--- a/gdb/testsuite/gdb.python/py-value-cc.cc
+++ b/gdb/testsuite/gdb.python/py-value-cc.cc
@@ -17,9 +17,18 @@
 
 class A {
  public:
+  int operator+ (const int a1);
+
+ public:
   int a;
 };
 
+int
+A::operator+ (const int a1)
+{
+  return a + a1;
+}
+
 union U {
   int a;
   char c;
@@ -88,5 +97,7 @@ main ()
 {
   A obj;
 
+  obj.a = 5;
+
   return func (obj);
 }
diff --git a/gdb/testsuite/gdb.python/py-value-cc.exp b/gdb/testsuite/gdb.python/py-value-cc.exp
index e6351f6..949f04f 100644
--- a/gdb/testsuite/gdb.python/py-value-cc.exp
+++ b/gdb/testsuite/gdb.python/py-value-cc.exp
@@ -99,3 +99,7 @@ gdb_test "python print xtd\[x_fields\[1\]\]\['a'\]" "102" "xtd->a via field"
 gdb_test "python print len(uu_fields)" "2" "number of fields in uu"
 gdb_test "python print uu\[uu_fields\[0\]\]\['x'\]" "1000" "uu.x via field"
 gdb_test "python print uu\[uu_fields\[1\]\]\['a'\]" "1000" "uu.a via field"
+
+# Test overloaded operators.
+gdb_test_no_output "python a = gdb.parse_and_eval('a')" "init a"
+gdb_test "python print a + 5" "10" "a + 5"