Re: gcc and -fPIC

[Gerhard Wiesinger <lists at wiesinger dot com>]

On Fri, 15 Oct 2004, Andreas Schwab wrote:

> Gerhard Wiesinger <gerhard@wiesinger.com> writes:
>
> > Why is there a call at location 80485b3?
>
> This is used to load the program counter since the x86 does not have a
> pc-relative addressing mode except in calls.  That's the only way to get
> the address of the GOT in position independ code.
>
> > So is the code gcc produces (in)correct, or objdump can't read any
> > Position Independent Code?
>
> Neither.

BTW: Is it possible to see the dynamic symbols in the disassembly? I don't 
see the call to operator delete[](void*) at location 8048592.
=======================================================================
g++ -fPIC -g testnew.cpp -o testnew
objdump -r -R --dynamic-syms --private-headers -S -C testnew | less -I
=======================================================================
DYNAMIC SYMBOL TABLE:
080483d0      DF *UND*  0000002a  GLIBCPP_3.2 operator delete(void*)
080483e0      DF *UND*  000004d1  CXXABI_1.2  __gxx_personality_v0
080483f0      DF *UND*  000000f3  GLIBC_2.0   __libc_start_main
080486c0 g    DO .rodata        00000004  Base        _IO_stdin_used
08048400      DF *UND*  00000039  GLIBCPP_3.2 operator new[](unsigned int)
08048410      DF *UND*  00000026  GLIBCPP_3.2 operator delete[](void*)
00000000  w   D  *UND*  00000000              _Jv_RegisterClasses
08048420      DF *UND*  000000a3  GLIBCPP_3.2 operator new(unsigned int)
00000000  w   D  *UND*  00000000              __gmon_start__

        delete x;
 8048578:       83 ec 0c                sub    $0xc,%esp
 804857b:       ff 75 f4                pushl  0xfffffff4(%ebp)
 804857e:       e8 4d fe ff ff          call   80483d0 <_init+0x28>
 8048583:       83 c4 10                add    $0x10,%esp
        delete [] xarray;
 8048586:       83 7d f0 00             cmpl   $0x0,0xfffffff0(%ebp)
 804858a:       74 0e                   je     804859a <main+0xba>
 804858c:       83 ec 0c                sub    $0xc,%esp
 804858f:       ff 75 f0                pushl  0xfffffff0(%ebp)
 8048592:       e8 79 fe ff ff          call   8048410 <_init+0x68>
 8048597:       83 c4 10                add    $0x10,%esp
}
 804859a:       b8 00 00 00 00          mov    $0x0,%eax
 804859f:       8d 65 f8                lea    0xfffffff8(%ebp),%esp
 80485a2:       5b                      pop    %ebx
 80485a3:       5e                      pop    %esi
 80485a4:       c9                      leave
 80485a5:       c3                      ret
=======================================================================

When I just disassemble the object file this works well (but not in the 
linked version above):
=======================================================================
g++ -fPIC -g -c testnew.cpp -o testnew.o
objdump -r --private-headers -S -C testnew.o | less -I
=======================================================================
       delete [] xarray;
  a6:   83 7d f0 00             cmpl   $0x0,0xfffffff0(%ebp)
  aa:   74 0e                   je     ba <main+0xba>
  ac:   83 ec 0c                sub    $0xc,%esp
  af:   ff 75 f0                pushl  0xfffffff0(%ebp)
  b2:   e8 fc ff ff ff          call   b3 <main+0xb3>
                        b3: R_386_PLT32 operator delete[](void*)
  b7:   83 c4 10                add    $0x10,%esp
}
=======================================================================

Any ideas to get the symbols also in the linked version?

Thank you.

Ciao,
Gerhard