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[PATCH 2/2] Support setting breakpoints on C++ method pointers


(Oops, I accidentally sent the older version of this patch a 2nd time.
Sorry for the noise.)

{ v2: I noticed that non-virtual method pointers are also affected by
this commit.  That is, breaking on non-virtual method pointers now also
works whereas previously it didn't.  So I rewrote the commit message and
augmented the testcase to also test non-virtual method pointers.  I also
tweaked the documentation for the function cplus_method_ptr_to_value(). }

-- >8 --

This patch adds support for setting breakpoints on C++ method pointers,
both virtual and non-virtual.  For example:

  struct x
  {
    virtual void f ();
    void g ();
  }

  void x::f () { }
  void x::g () { }

  struct y : x
  {
  }

(gdb) break *&y::f
Value can't be converted to integer.
(gdb) break *&y::g
Value can't be converted to integer.

Breaking on these expressions doesn't currently work because GDB doesn't
know how to convert a METHODPTR to an address in the function
value_as_address().  We have to teach value_as_address() how to extract
a symbolic address out from a METHODPTR in order for the above example
to work.

This patch tweaks value_as_address() to call cplus_method_ptr_to_value()
in order to extract a pointer value out of a METHODPTR.  The latter
function does most of the work, but it needs a few tweaks.  Firstly,
this patch makes the first argument of gnuv3_method_ptr_to_value(), i.e.
the argument corresponding to a "this" object pointer, optional.
Secondly, when the "this" pointer is omitted and a virtual method
pointer is passed in then we attempt to extract a pointer value by doing
a lookup of the virtual method pointer's symbolic name in the symbol
table.

Tested on x86_64-unknown-linux-gnu.

gdb/ChangeLog
	* cp-abi.h (cplus_method_ptr_to_value): Document behavior for a
	THIS_P that's NULL.
	* gnu-v3-abi.c (gnuv3_method_ptr_to_value): Support method
	resolution without a given "this" object.
	* value.c (value_as_address): Handle TYPE_CODE_METHODPTR values.

gdb/testsuite/ChangeLog
	* gdb.cp/method-ptr.exp: Add tests for breaking on non-virtual
	method pointers.
	(check_virtual_method_ptr_resolution): New parameter VIRTUAL.
	Also test that setting a breakpoint on the given method pointer
	works correctly.
	* gdb.cp/method-ptr.cc: Introduce a few non-virtual methods
	to test.
---
 gdb/cp-abi.h                        |  4 ++-
 gdb/gnu-v3-abi.c                    | 65 +++++++++++++++++++++++++------------
 gdb/testsuite/gdb.cp/method-ptr.cc  |  6 ++++
 gdb/testsuite/gdb.cp/method-ptr.exp | 23 +++++++++++--
 gdb/value.c                         |  8 +++++
 5 files changed, 81 insertions(+), 25 deletions(-)

diff --git a/gdb/cp-abi.h b/gdb/cp-abi.h
index 7d4b7f3..1f38605 100644
--- a/gdb/cp-abi.h
+++ b/gdb/cp-abi.h
@@ -162,7 +162,9 @@ void cplus_print_method_ptr (const gdb_byte *contents,
 int cplus_method_ptr_size (struct type *to_type);
 
 /* Return the method which should be called by applying METHOD_PTR to
-   *THIS_P, and adjust *THIS_P if necessary.  */
+   *THIS_P, and adjust *THIS_P if necessary.  If THIS_P is NULL then
+   return the method that would be called if METHOD_PTR was applied
+   to an object of METHOD_PTR's domain type (e.g. the type X in &X::f).  */
 struct value *cplus_method_ptr_to_value (struct value **this_p,
 					 struct value *method_ptr);
 
diff --git a/gdb/gnu-v3-abi.c b/gdb/gnu-v3-abi.c
index ccb0be6..718694b 100644
--- a/gdb/gnu-v3-abi.c
+++ b/gdb/gnu-v3-abi.c
@@ -719,36 +719,59 @@ gnuv3_method_ptr_to_value (struct value **this_p, struct value *method_ptr)
   gdbarch = get_type_arch (domain_type);
   vbit = gnuv3_decode_method_ptr (gdbarch, contents, &ptr_value, &adjustment);
 
-  /* First convert THIS to match the containing type of the pointer to
-     member.  This cast may adjust the value of THIS.  */
-  *this_p = value_cast (final_type, *this_p);
+  if (this_p != NULL)
+    {
+      /* First convert THIS to match the containing type of the pointer to
+         member.  This cast may adjust the value of THIS.  */
+      *this_p = value_cast (final_type, *this_p);
 
-  /* Then apply whatever adjustment is necessary.  This creates a somewhat
-     strange pointer: it claims to have type FINAL_TYPE, but in fact it
-     might not be a valid FINAL_TYPE.  For instance, it might be a
-     base class of FINAL_TYPE.  And if it's not the primary base class,
-     then printing it out as a FINAL_TYPE object would produce some pretty
-     garbage.
+      /* Then apply whatever adjustment is necessary.  This creates a somewhat
+         strange pointer: it claims to have type FINAL_TYPE, but in fact it
+         might not be a valid FINAL_TYPE.  For instance, it might be a
+         base class of FINAL_TYPE.  And if it's not the primary base class,
+         then printing it out as a FINAL_TYPE object would produce some pretty
+         garbage.
 
-     But we don't really know the type of the first argument in
-     METHOD_TYPE either, which is why this happens.  We can't
-     dereference this later as a FINAL_TYPE, but once we arrive in the
-     called method we'll have debugging information for the type of
-     "this" - and that'll match the value we produce here.
+         But we don't really know the type of the first argument in
+         METHOD_TYPE either, which is why this happens.  We can't
+         dereference this later as a FINAL_TYPE, but once we arrive in the
+         called method we'll have debugging information for the type of
+         "this" - and that'll match the value we produce here.
 
-     You can provoke this case by casting a Base::* to a Derived::*, for
-     instance.  */
-  *this_p = value_cast (builtin_type (gdbarch)->builtin_data_ptr, *this_p);
-  *this_p = value_ptradd (*this_p, adjustment);
-  *this_p = value_cast (final_type, *this_p);
+         You can provoke this case by casting a Base::* to a Derived::*, for
+         instance.  */
+      *this_p = value_cast (builtin_type (gdbarch)->builtin_data_ptr, *this_p);
+      *this_p = value_ptradd (*this_p, adjustment);
+      *this_p = value_cast (final_type, *this_p);
+    }
 
   if (vbit)
     {
       LONGEST voffset;
 
       voffset = ptr_value / TYPE_LENGTH (vtable_ptrdiff_type (gdbarch));
-      return gnuv3_get_virtual_fn (gdbarch, value_ind (*this_p),
-				   method_type, voffset);
+
+      /* If we don't have a "this" object to apply the method pointer to,
+	 then retrieve the value of the virtual method by looking up its
+	 symbolic name within the symbol table.  */
+      if (this_p == NULL)
+	{
+	  const char *physname;
+	  struct symbol *sym;
+
+	  physname = gnuv3_find_method_in (domain_type, voffset, adjustment);
+	  if (physname == NULL)
+	    return NULL;
+
+	  sym = lookup_symbol (physname, NULL, VAR_DOMAIN, NULL);
+	  if (sym == NULL)
+	    return NULL;
+
+	  return value_of_variable (sym, NULL);
+	}
+      else
+        return gnuv3_get_virtual_fn (gdbarch, value_ind (*this_p),
+				     method_type, voffset);
     }
   else
     return value_from_pointer (lookup_pointer_type (method_type), ptr_value);
diff --git a/gdb/testsuite/gdb.cp/method-ptr.cc b/gdb/testsuite/gdb.cp/method-ptr.cc
index db47484..4e1524a 100644
--- a/gdb/testsuite/gdb.cp/method-ptr.cc
+++ b/gdb/testsuite/gdb.cp/method-ptr.cc
@@ -20,11 +20,14 @@ struct x
   virtual void f ();
   virtual void g ();
   virtual void h ();
+
+  void a ();
 };
 
 void x::f () { }
 void x::g () { }
 void x::h () { }
+void x::a () { }
 
 struct y : x
 {
@@ -32,11 +35,14 @@ struct y : x
 
   virtual void j ();
   virtual void k ();
+
+  void b ();
 };
 
 void y::f () { }
 void y::j () { }
 void y::k () { }
+void y::b () { }
 
 struct z : y
 {
diff --git a/gdb/testsuite/gdb.cp/method-ptr.exp b/gdb/testsuite/gdb.cp/method-ptr.exp
index 732b861..ca6be4b 100644
--- a/gdb/testsuite/gdb.cp/method-ptr.exp
+++ b/gdb/testsuite/gdb.cp/method-ptr.exp
@@ -33,23 +33,38 @@ if ![test_debug_format "DWARF 2"] {
     return 0
 }
 
-# Check that the virtual method pointer NAME resolves to symbol SYMBOL.
-proc check_virtual_method_ptr_resolution { name symbol } {
+# Check that the method pointer NAME resolves to symbol SYMBOL.  Set VIRTUAL
+# to 1 if NAME is a virtual method pointer (default), 0 otherwise.
+proc check_virtual_method_ptr_resolution { name symbol {virtual 1} } {
     global decimal
 
     # Printing the expression &NAME should show the resolved symbol SYMBOL.
-    gdb_test "print &$name" "\\$$decimal = &virtual $symbol\\(\\)\\s"
+    if {$virtual != 0} {
+        gdb_test "print &$name" "\\s&virtual $symbol\\(\\)\\s"
+    } else {
+        gdb_test "print &$name" "\\s<$symbol\\(\\)>\\s"
+    }
+
+    # Breaking on the expression &NAME should create a breakpoint on the symbol
+    # SYMBOL.
+    set breakpoint_line [gdb_get_line_number $symbol]
+    gdb_test "break *&$name" \
+             "Breakpoint $decimal at .*, line $breakpoint_line\\.\\s"
+    delete_breakpoints
 }
 
 check_virtual_method_ptr_resolution "x::f" "x::f"
 check_virtual_method_ptr_resolution "x::g" "x::g"
 check_virtual_method_ptr_resolution "x::h" "x::h"
+check_virtual_method_ptr_resolution "x::a" "x::a" 0
 
 check_virtual_method_ptr_resolution "y::f" "y::f"
 check_virtual_method_ptr_resolution "y::g" "x::g"
 check_virtual_method_ptr_resolution "y::h" "x::h"
 check_virtual_method_ptr_resolution "y::j" "y::j"
 check_virtual_method_ptr_resolution "y::k" "y::k"
+check_virtual_method_ptr_resolution "y::a" "x::a" 0
+check_virtual_method_ptr_resolution "y::b" "y::b" 0
 
 check_virtual_method_ptr_resolution "z::f" "y::f"
 check_virtual_method_ptr_resolution "z::g" "z::g"
@@ -58,3 +73,5 @@ check_virtual_method_ptr_resolution "z::j" "z::j"
 check_virtual_method_ptr_resolution "z::k" "y::k"
 check_virtual_method_ptr_resolution "z::l" "z::l"
 check_virtual_method_ptr_resolution "z::m" "z::m"
+check_virtual_method_ptr_resolution "z::a" "x::a" 0
+check_virtual_method_ptr_resolution "z::b" "y::b" 0
diff --git a/gdb/value.c b/gdb/value.c
index fdc8858d..63ff363 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -2639,6 +2639,14 @@ value_as_address (struct value *val)
   return gdbarch_addr_bits_remove (gdbarch, value_as_long (val));
 #else
 
+  if (TYPE_CODE (value_type (val)) == TYPE_CODE_METHODPTR)
+    {
+      val = cplus_method_ptr_to_value (NULL, val);
+      if (val == NULL)
+	error (_("Method pointer can't be converted to an address."));
+    }
+
+
   /* There are several targets (IA-64, PowerPC, and others) which
      don't represent pointers to functions as simply the address of
      the function's entry point.  For example, on the IA-64, a
-- 
2.1.1.273.g97b8860


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