Re: debug/8095: missing dwarf info for parent class

[Daniel Jacobowitz <drow@mvista.com>]

The following reply was made to PR debug/8095; it has been noted by GNATS.

From: Daniel Jacobowitz <drow@mvista.com>
To: Horsley Tom <Tom.Horsley@ccur.com>
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: debug/8095: missing dwarf info for parent class
Date: Tue, 1 Oct 2002 15:06:44 -0400

 On Tue, Oct 01, 2002 at 08:02:44AM -0400, Horsley Tom wrote:
 > > -----Original Message-----
 > > From: Daniel Jacobowitz [mailto:drow@mvista.com]
 > > Sent: Monday, September 30, 2002 4:38 PM
 > > To: tom.horsley@ccur.com
 > > Cc: gcc-gnats@gcc.gnu.org
 > > Subject: Re: debug/8095: missing dwarf info for parent class
 > >...
 > > Please provide a test case.
 > 
 > Weird. Every program I have exhibits this behavior. Here's
 > a random test program I picked this morning on my first try :-).
 > 
 > class Vtab1 {
 > public:
 >    Vtab1();
 >    Vtab1(int init_x);
 >    virtual
 >    ~Vtab1();
 >    virtual int
 >    GetX();
 > private:
 >    int x;
 > };
 > class Vtab2 {
 > public:
 >    Vtab2();
 >    Vtab2(int init_y);
 >    virtual
 >    ~Vtab2();
 >    virtual int
 >    GetY();
 > private:
 >    int y;
 > };
 > class Multiple1 : public Vtab1, public Vtab2 {
 > public:
 >    Multiple1(int init_x, int init_y, int init_z);
 >    virtual
 >    ~Multiple1();
 >    virtual int
 >    GetZ();
 > private:
 >    int z;
 > };
 > class Derived1 : public Multiple1 {
 > public:
 >    Derived1(int init_x, int init_y, int init_z);
 >    virtual
 >    ~Derived1();
 >    virtual int
 >    GetX();
 > private:
 >    int my_x;
 > };
 > Derived1::Derived1(int init_x, int init_y, int init_z)
 >  : Multiple1(init_x, init_y, init_z) {
 >    my_x = GetY();
 > }
 > Derived1::~Derived1() {
 >    return;
 > }
 > int
 > Derived1::GetX() {
 >    return my_x;
 > }
 > 
 > Using g++ 3.2 (Red Hat Linux Rawhide 3.2-1), if I compile
 > this as g++ -g -c d1.cpp and examine the dwarf in the d1.o file,
 > no symbols named "x","y", or "z" appear anywhere, and the
 > parent class info for Derived1 points to a DW_AT_declaration
 > for Multiple1, but there is no corresponding class definition
 > with a DW_AT_specification pointing to that Multiple1, so
 > no definition is available anywhere for the actual contents
 > of the parent classes, yet they are certainly used since
 > the type of the "this" pointer in the member functions
 > refers to them indirectly.
 
 OK.  The reason that debug info for (for example) Vtab1 is not emitted
 is because it contains unimplemented virtual functions which are not
 declared as abstract.  Thus the vtable for Vtab1 is not emitted, and
 the debug information appears to be tied to that.
 
 I could make a good argument that this isn't right.  Can a C++
 maintainer comment?
 
 -- 
 Daniel Jacobowitz
 MontaVista Software                         Debian GNU/Linux Developer