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3.4 Debugging executables

If hell was a complicated program, you would certainly want to test and debug it before installing it on your system. In the above section, you saw how the libtool wrapper script makes it possible to run the program directly, but unfortunately, this mechanism interferes with the debugger:

     burger$ gdb hell
     GDB is free software and you are welcome to distribute copies of it
      under certain conditions; type "show copying" to see the conditions.
     There is no warranty for GDB; type "show warranty" for details.
     GDB 4.16 (i386-unknown-netbsd), (C) 1996 Free Software Foundation, Inc.
     
     "hell": not in executable format: File format not recognized
     
     (gdb) quit
     burger$

Sad. It doesn't work because GDB doesn't know where the executable lives. So, let's try again, by invoking GDB directly on the executable:

     burger$ gdb .libs/hell
     GNU gdb 5.3 (i386-unknown-netbsd)
     Copyright 2002 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 no warranty for GDB.  Type "show warranty" for details.
     (gdb) break main
     Breakpoint 1 at 0x8048547: file main.c, line 29.
     (gdb) run
     Starting program: /home/src/libtool/demo/.libs/hell
     /home/src/libtool/demo/.libs/hell: can't load library 'libhello.so.0'
     
     Program exited with code 020.
     (gdb) quit
     burger$

Argh. Now GDB complains because it cannot find the shared library that hell is linked against. So, we must use libtool in order to properly set the library path and run the debugger. Fortunately, we can forget all about the .libs directory, and just run it on the executable wrapper (see Execute mode):

     burger$ libtool --mode=execute gdb hell
     GNU gdb 5.3 (i386-unknown-netbsd)
     Copyright 2002 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 no warranty for GDB.  Type "show warranty" for details.
     (gdb) break main
     Breakpoint 1 at 0x8048547: file main.c, line 29.
     (gdb) run
     Starting program: /home/src/libtool/demo/.libs/hell
     
     Breakpoint 1, main (argc=1, argv=0xbffffc40) at main.c:29
     29        printf ("Welcome to GNU Hell!\n");
     (gdb) quit
     The program is running.  Quit anyway (and kill it)? (y or n) y
     burger$