[PyKDE] FYI, Things we learned, when trying to load SIPed shared libraries.

[Stephan Koerner]

Just thought I'd share some of our experiences with the chance it might
help someone else.

stephan

Revised: 2001-08-23

Subject: Things we learned, when trying to load SIPed shared libraries.

When faced with an Import Error or core dump upon an import, the following 
where a few steps we found helpful to track down shared library loading issues.  


1) Fire-up Python with the `-v -v' option just to make certain Python
   is importing the module/library you expect it to be picking up.  

2) For diagnostic purposes do an import on the library directly rather than
   the pure python helper file. 
     Example:  "import libqtc  rather than import qt"

3) Take a look inside the SIPed generated library, to see what it depends on.
   There are different commands on the respective operating systems
   to do this.

     AIX    `dump -H    lib<foo>c.so `
     HP-UX  `chatr      lib<foo>c.sl `
     IRIX   `elfdump -L lib<foo>c.so `
     SunOS  `ldd        lib<foo>c.so `
     NT      dumpbin /DEPENDENTS  lib<foo>c.dll   
             the "Dependency Walker" which comes with
             the Dev Studio tools is also handy.

4) Shared Library paths?
   On the various operating systems the loaders often take cues from
   environment variables to find shared libraries.
   This bares investigation, only after you are certain that Python is
   finding the SIPed library properly and now you are fighting an issue
   that the SIPed library is trying to pull in another library.  
   (Python finds the initial SIPed shared library by way of the normal
    python path search) 
   The following are some of the environment variables the loaders reference.
     
      AIX        $LIBPATH
      HP-UX      $SHLIB_PATH
      IRIX       $LD_LIBRARY_PATH,   $LD_LIBRARYN32_PATH
      SunOS      $LD_LIBRARY_PATH
         `env | grep LIB`

5) What's really happening when the loader is trying to pull in 
   lib<foo>c.s[ol] but fails.  It seems some operating systems
   offer a clue as to why a load may have failed, others don't
   offer as much information as desired.

   To help diagnose what might be happening try the following.
   Example is for AIX.  
    - create a dummy main()  with nothing in it ( foo.cxx)
      echo 'int main(int argc, char **argv){return 1;)} > foo.cxx
    - Link this against the library in question
      xlC foo.cxx  libqtcmodule.so 
    - Run the resulting executable
      ./a.out
    - Watch all those unresolved symbols scroll by  
    - This operation might highlight what subordinate libraries might have
      problems being loaded.   
     
    




Saga:
  The following are a couple things which happened to us on the way to 
  getting a SIPed-PyQt application running.   This application uses PyQt
  and we generate our own SIPed modules/libraries.  So you will see
  in our application
     import qt                 # which then import libqtcmodule.s[ol]
     import ourCompiledCode    # which then import libourCompiledCode.s[ol]
     .
     .


  Scenario 1) 
     We could import the respective modules/libraries individually but not
     together.  If both where imported python would core dump.

     The respective libraries  libqtcmodule.sl and libourCompiledCodec.sl
     where loading two different libsip.sl libraries.  (One library was
     picking up the libsip.sl from the build environ and the other was
     picking it up from the release environ)  (I hate it, when that happens;-)
     Combination of  using `chatr` and the `dde` debugger helped track this
     problem down.  (Depending on how you link the .sl there might be an
     internal reference with a full file spec pointing to it's dependent
     libraries.  Hence the `chatr` command comes in handy. ) (Try looking
     at the HP-UX link option +cdp )

  Scenario 2)
     Under AIX use the -brtl option on the link command otherwise the 
     libraries won't look for .so files to pull in.


Thanks to:  
   The person that posted there steps in
   hpux_install_notes.txt and solaris_install_notes.txt
   If anyone remembers who this was could you send me there e-mail address


Prepared: skoer at adams.com

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