[SOLVED] Any option in GCC to SEE the dynamic bindings processing happening, in the compilation output?

Aquarius_Girl · 02-19-2011, 01:53 AM

No, I am not talking about linking the dynamic libraries,
I am talking about the dynamic binding happening w.r.t
the virtual functions.

Kenny_Strawn · 02-20-2011, 10:51 AM

Well, make does post output, but not GCC. Of course, you do get error messages from GCC, but that's normal. I suppose if you have enough programming skills you could fork GCC to make it display a progress bar or something (or maybe create a GUI frontend to GCC), but either of these things would be pushing it.

wje_lq · 02-21-2011, 07:25 PM

Quote:

Originally Posted by Anisha Kaul

No, I am not talking about linking the dynamic libraries,
I am talking about the dynamic binding happening w.r.t
the virtual functions.

C++, right? It's been a while since I've used virtual functions, or even C++. Could you illustrate with a tiny, compilable C++ program we can play around with?

Aquarius_Girl · 02-21-2011, 07:28 PM

Thanks a ton for responding wje_lq,

I thought I asked a pathetic question

I have an example too and have found a possible solution option too, but
it doesn't seem to work

, soon I'll present them here.

Aquarius_Girl · 02-21-2011, 11:32 PM

Yeah on C++, but could have been Java too, how did you guess it?

With respect to this quote:

Code:

G++'s -fdump-class-hierarchy argument can be used to dump virtual method tables for manual inspection.

from this link: http://en.wikipedia.org/wiki/Virtual_method_table

I tried the following:

Code:

#include <iostream>
using namespace std;

class a
{
     public:
	  virtual void f1 ();
};

void a :: f1 () {}

class b : public a
{
     public:
	  void f1 ();
};

void b :: f1 () {}

int main ()
{
     b obj1;
     obj1.f1 ();
     
     return 0;
}

Its compilation output shows NOTHING

Code:

anisha@linux-uitj:~> g++ -Wall -Wextra virtual.cpp -fdump-class-hierarchy
anisha@linux-uitj:~>

wje_lq · 02-22-2011, 05:08 AM

When I ran this shell script:

Code:

rm -f *.class; cat > virtual.cpp <<EOD; g++ -Wall -Wextra virtual.cpp -fdump-class-hierarchy; ls -l virtual*.class; cat virtual*.class
#include <iostream>
using namespace std;

class a
{
     public:
          virtual void f1 ();
};

void a :: f1 () {}

class b : public a
{
     public:
          void f1 ();
};

void b :: f1 () {}

int main ()
{
     b obj1;
     obj1.f1 ();
     
     return 0;
}
EOD

I got this output (snipped in the middle for brevity):

Code:

-rw------- 1 wally wally 67688 Feb 22 02:57 virtual.cpp.002t.class
Class <anonymous struct>::<anonymous union>
   size=4 align=4
   base size=4 base align=4
<anonymous struct>::<anonymous union> (0xb777c078) 0

Class <anonymous struct>
   size=8 align=4
   base size=8 base align=4
<anonymous struct> (0xb777c000) 0

Class __locale_struct
   size=116 align=4
   base size=116 base align=4
__locale_struct (0xb777c0b4) 0

Vtable for std::exception
std::exception::_ZTVSt9exception: 5u entries
0     (int (*)(...))0
4     (int (*)(...))(& _ZTISt9exception)
8     std::exception::~exception
12    std::exception::~exception
16    std::exception::what

Class std::exception
   size=4 align=4
   base size=4 base align=4
std::exception (0xb777c708) 0 nearly-empty
    vptr=((& std::exception::_ZTVSt9exception) + 8u)

---------->8---------->8---------->8----------

Class std::basic_iostream<wchar_t, std::char_traits<wchar_t> >
   size=152 align=4
   base size=12 base align=4
std::basic_iostream<wchar_t, std::char_traits<wchar_t> > (0xb706ebd0) 0
    vptridx=0u vptr=((& std::basic_iostream<wchar_t, std::char_traits<wchar_t> >::_ZTVSt14basic_iostreamIwSt11char_traitsIwEE) + 12u)
  std::basic_istream<wchar_t, std::char_traits<wchar_t> > (0xb7252840) 0
      primary-for std::basic_iostream<wchar_t, std::char_traits<wchar_t> > (0xb706ebd0)
      subvttidx=4u
    std::basic_ios<wchar_t, std::char_traits<wchar_t> > (0xb7252880) 12 virtual
        vptridx=20u vbaseoffset=-0x0000000000000000c vptr=((& std::basic_iostream<wchar_t, std::char_traits<wchar_t> >::_ZTVSt14basic_iostreamIwSt11char_traitsIwEE) + 52u)
      std::ios_base (0xb721da14) 12
          primary-for std::basic_ios<wchar_t, std::char_traits<wchar_t> > (0xb7252880)
  std::basic_ostream<wchar_t, std::char_traits<wchar_t> > (0xb72528c0) 8 nearly-empty
      subvttidx=12u vptridx=24u vptr=((& std::basic_iostream<wchar_t, std::char_traits<wchar_t> >::_ZTVSt14basic_iostreamIwSt11char_traitsIwEE) + 32u)
    std::basic_ios<wchar_t, std::char_traits<wchar_t> > (0xb7252880) alternative-path

Vtable for a
a::_ZTV1a: 3u entries
0     (int (*)(...))0
4     (int (*)(...))(& _ZTI1a)
8     a::f1

Class a
   size=4 align=4
   base size=4 base align=4
a (0xb721ddd4) 0 nearly-empty
    vptr=((& a::_ZTV1a) + 8u)

Vtable for b
b::_ZTV1b: 3u entries
0     (int (*)(...))0
4     (int (*)(...))(& _ZTI1b)
8     b::f1

Class b
   size=4 align=4
   base size=4 base align=4
b (0xb7252a40) 0 nearly-empty
    vptr=((& b::_ZTV1b) + 8u)
  a (0xb721dfb4) 0 nearly-empty
      primary-for b (0xb7252a40)

Is this what you wanted?

Aquarius_Girl · 02-22-2011, 05:40 AM

Exactly, that's what I was looking for, but I didn't know that that
option produced some output files

, now when I do ls, I
see a dozen!

I shall try to understand that vtable now. Thanks again.

(All that's for understanding the conceptual differences between
static and dynamic bindings

)

wje_lq · 02-22-2011, 11:56 AM

Quote:

Originally Posted by Anisha Kaul

I didn't know that that option produced some output files

Um, I didn't know until I read the man page for g++ this morning. :)

Aquarius_Girl · 02-23-2011, 01:19 AM

I too had read the man page but only uptill here:

Code:

Debugging Options
           -dletters  -dumpspecs  -dumpmachine  -dumpversion -fdbg-cnt-list -fdbg-cnt=counter-value-
           list -fdump-noaddr -fdump-unnumbered -fdump-translation-unit[-n] -fdump-class-hierarchy[-n]
           -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline -fdump-statistics -fdump-tree-all
           -fdump-tree-original[-n] -fdump-tree-optimized[-n] -fdump-tree-cfg -fdump-tree-vcg
           -fdump-tree-alias -fdump-tree-ch -fdump-tree-ssa[-n] -fdump-tree-pre[-n]
           -fdump-tree-ccp[-n] -fdump-tree-dce[-n] -fdump-tree-gimple[-raw] -fdump-tree-mudflap[-n]
           -fdump-tree-dom[-n] -fdump-tree-dse[-n] -fdump-tree-phiopt[-n] -fdump-tree-forwprop[-n]
           -fdump-tree-copyrename[-n] -fdump-tree-nrv -fdump-tree-vect -fdump-tree-sink

How could I have guessed that I need to scroll till end!