Crashes with shared libs - where can I learn more about shared libs and ld?

From: Carsten Fuchs (CarstenFuchs_at_T-Online.de)
Date: 05/11/05

  • Next message: Paul Pluzhnikov: "Re: Crashes with shared libs - where can I learn more about shared libs and ld?" 
    Date: Wed, 11 May 2005 17:04:47 +0200

    Dear ng,

    I'm currently working on a rather big g++ program. The program compiles
    and links just fine and without warnings. During run-time, it
    dynamically loads shared libs with dlopen().

    However, running the program frequently yields "Segmentation fault" or
    "Illegal instruction" aborts. These aborts occur for example when code
    within a shared lib accesses static variables of the main program (e.g.
    via a pointer or reference to that static variable).
    I tried to employ the gdb / ddd debuggers in order to track the cause
    for the crashes down, but was not able to obtain any helpful insight.

    The symptoms (occurring/disappearing of the crashes) change when for
    example an .o file is linked to the main program that however is not
    required for normal linking of the main program otherwise.

    I've already read resources like
    http://www.gnu.org/software/binutils/manual/ld-2.9.1/ld.html
    http://en.tldp.org/HOWTO/Program-Library-HOWTO/index.html

    Although the compile and link produces no warnings or errors, I feel
    that I'm still compiling and/or linking the main program or the shared
    libs in a wrong manner, but I was not able to deduce the origin of the
    problems from the docs alone.

    - Is compiling with -fpic strictly required for shared libs?
    - Can a specific .o file (either being compiled with or without -fpic)
    be linked both to a shared lib as well as to the main program, and the
    resulting shared lib be dlopen()'ed into the main program?
    - What are the "semantic" differences between Linux shared libs and
    Windows DLLs? My program runs just fine under Windows, and I'm much more
    familiar with the semantics of Windows DLLs than those of Linux shared
    libs. (Grossly spoken: DLLs are "separate, individual programs" that
    are reference-counted if multiple instances are loaded, whereas shared
    libs...?)

    Summarizing this yields my question from above:
    Where and how can I learn more about shared libs and ld?

    Alternatively, can somebody give me a hint about factors that can cause
    shared libs to trigger aborts like "Illegal instruction"?

    I'm aware that the above is only a very gross description of the
    problem. I'd be happy to supply more details - if only I know which
    details are relevant. (I've tried many things during the past few days,
    and thus rather post an overview here first.)

    Thank you very much for your help!

    Best regards,
    Carsten 

    -- 
Ca3D - Engine    http://www.Ca3D-Engine.de
Carsten Fuchs    http://www.Ca3D-Engine.de/c_Carsten.php
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