Problem debugging statically linked c++ program with GDB 6.0

Problem debugging statically linked c++ program with GDB 6.0

[Holger Sesterhenn]

Hi,

I have a bug in my statically linked c++ program and would like to use
DDD with GDB to see whats wrong. I use <string> from the stdlibc++.
DDD/GDB shows a SIGSGV if I call a member function e.g. c_str() to take
a look at the value of the string.

I have written a little program to reproduce the problem (don't need
DDD). If the program is linked dynamically, everything works as expected!

If somebody can confirm the problem I would submit a bug report.
Searching the bug database I did not find any hint.

Running Linux 2.4.21 (IA86/32), compiled gcc 3.3.3, glibc 2.3.2 and gdb
6.0 myself (chrooted). The problem can be reproduced with a plain SuSE
9.0 installation (gcc 3.3.1, glibc 2.3.2, gdb 5.3.92).

Here is my screen dump.

#>g++ -g -static mytest.cpp
######################################
#>../gdb-6.0/gdb/gdb ./a.out
GNU gdb 6.0
Copyright 2003 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i686-pc-linux-gnu"...
(gdb) l
1       #include <string>
2       #include <iostream>
3
4       int main () {
5               std::string a("Hello");
6
7               std::cout << a << std::endl;
8       } // main()
9
(gdb) b 7
Breakpoint 1 at 0x8048254: file mytest.cpp, line 7.
(gdb) r
Starting program: /src/fw/proxy/smtp/smtpd/test/a.out

Breakpoint 1, main () at mytest.cpp:7
7               std::cout << a << std::endl;
(gdb) p a
$1 = {static npos = 4294967295, _M_dataplus = {<allocator<char>> =
 {<No data fields>}, _M_p = 0x8117d2c "Hello"},
  static _S_empty_rep_storage = {0, 0, 0, 0}}
(gdb) p a.c_str()

Program received signal SIGSEGV, Segmentation fault.
0x08088546 in __libc_start_main ()
The program being debugged was signaled while in a function called from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwindonsignal on"
Evaluation of the expression containing the function
(std::string::c_str() const) will be abandoned.
(gdb)
#########################################
#>/lib/libc.so.6
GNU C Library stable release version 2.3.2, by Roland McGrath et al.
Copyright (C) 2003 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 3.3.3.
Compiled on a Linux 2.4.23 system on 2004-04-01.
Available extensions:
        GNU libio by Per Bothner
        crypt add-on version 2.1 by Michael Glad and others
        linuxthreads-0.10 by Xavier Leroy
        BIND-8.2.3-T5B
        libthread_db work sponsored by Alpha Processor Inc
        NIS(YP)/NIS+ NSS modules 0.19 by Thorsten Kukuk
Report bugs using the `glibcbug' script to <bugs@gnu.org>.
##########################################

#>g++ -g mytest.cpp

#>ldd a.out
        libstdc++.so.5 => /usr/lib/libstdc++.so.5 (0x40015000)
        libm.so.6 => /lib/libm.so.6 (0x4013f000)
        libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x40162000)
        libc.so.6 => /lib/libc.so.6 (0x401cf000)
        /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)


######################################
#>../gdb-6.0/gdb/gdb ./a.out
GNU gdb 6.0
Copyright 2003 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i686-pc-linux-gnu"...
(gdb) b 7
Breakpoint 1 at 0x80488c8: file mytest.cpp, line 7.
(gdb) r
Starting program: /src/fw/proxy/smtp/smtpd/test/a.out

Breakpoint 1, main () at mytest.cpp:7
7               std::cout << a << std::endl;
(gdb) p a
$1 = {static npos = 4294967295, _M_dataplus = {<allocator<char>> = {<No
data fields>}, _M_p = 0x8049db4 "Hello"},
  static _S_empty_rep_storage = {0, 0, 0, 0}}
(gdb) p a.c_str()
$2 = 0x8049db4 "Hello"
########################################

Any hints?

-- 
Best Regards,

Holger Sesterhenn
---
Internet   http://www.utimaco.com

Re: Problem debugging statically linked c++ program with GDB 6.0

[Bob Rossi]

On Fri, Apr 02, 2004 at 02:07:38PM +0200, Holger Sesterhenn wrote:
> Hi,
> 
> I have a bug in my statically linked c++ program and would like to use
> DDD with GDB to see whats wrong. I use <string> from the stdlibc++.
> DDD/GDB shows a SIGSGV if I call a member function e.g. c_str() to take
> a look at the value of the string.
> 
> I have written a little program to reproduce the problem (don't need
> DDD). If the program is linked dynamically, everything works as expected!
> 
> If somebody can confirm the problem I would submit a bug report.
> Searching the bug database I did not find any hint.
> 
> Running Linux 2.4.21 (IA86/32), compiled gcc 3.3.3, glibc 2.3.2 and gdb
> 6.0 myself (chrooted). The problem can be reproduced with a plain SuSE
> 9.0 installation (gcc 3.3.1, glibc 2.3.2, gdb 5.3.92).

I don't know if this is helpful, however, GDB crashes for me even when I
link dynamically. It will only evaluate the expression sometimes for me.

Because of this, I have added the snippet below to my .gdbinit file

   # prints a C++ string
   define pc
      set $string_length=$arg0.length()
      set print elements $string_length
      print $arg0.dat
      set print elements 0
   end

   document pc
      Prints a C++ string
   end
   
This seems to work ok, even though it's not the perfect solution.
For some reason calling the length() function never seems to crash for
me.

Bob Rossi

Re: Problem debugging statically linked c++ program with GDB 6.0

[Holger Sesterhenn]

Hi,

> Because of this, I have added the snippet below to my .gdbinit file
[...]
> This seems to work ok, even though it's not the perfect solution.
> For some reason calling the length() function never seems to crash for
> me.

Thank you for the quick response but unfortunately this does not work
for me either.

Looks like there is a general problem calling methods. 'call a.c_str()'
crashes, too!

Best Regards,

Holger Sesterhenn
---
Internet   http://www.utimaco.com

Re: Problem debugging statically linked c++ program with GDB 6.0

[Bob Rossi]

On Fri, Apr 02, 2004 at 04:47:55PM +0200, Holger Sesterhenn wrote:
> Hi,
> 
> > Because of this, I have added the snippet below to my .gdbinit file
> [...]
> > This seems to work ok, even though it's not the perfect solution.
> > For some reason calling the length() function never seems to crash for
> > me.
> 
> Thank you for the quick response but unfortunately this does not work
> for me either.
> 
> Looks like there is a general problem calling methods. 'call a.c_str()'
> crashes, too!

Interesting, why doesn't my solution work?

Bob Rossi

Re: Problem debugging statically linked c++ program with GDB 6.0

[Holger Sesterhenn]

Hi,

Bob Rossi wrote:

>>Looks like there is a general problem calling methods. 'call a.c_str()'
>>crashes, too!
> Interesting, why doesn't my solution work?

I don't know but ...

I have just compiled the new GDB 6.1 and IT WORKS!

No SIGSEGV when calling a method of an object.

-- 
Best Regards,

Holger Sesterhenn
---
Internet   http://www.utimaco.com