Re: environ symbol on MacOS X with EPICS base 3.14.10

[Bill Lavender <lavender@agni.phys.iit.edu>]

OK.  Thanks for the information.

Bill Lavender

On Mon, Mar 23, 2009 at 03:38:36PM -0500, Eric Norum wrote:
> This change is in the CVS repository for the R3.14 branch and the CVS  
> head.
>
> On Mar 23, 2009, at 3:05 PM, Bill Lavender wrote:
>
>> I have encountered a minor problem with EPICS base 3.14.10 on MacOS X
>> systems that I would like to report.  In my situation, I have a Python
>> module coded in C that invokes a library of mine, which in turn links
>> to the EPICS libCom and libca libraries.  The symptom of the problem  
>> is
>> that when I try to import the Python module, I get an error like this:
>>
>> ImportError: dlopen(./MpPrivate.so, 2): Symbol not found: _environ
>>  Referenced from: /opt/epics/base-3.14.10/lib/darwin-x86/libCom. 
>> 3.14.10.dylib
>>  Expected in: flat namespace
>>
>> This is on a computer running MacOS X 10.5 (Leopard).
>>
>> The source of the problem is that MacOS X defines the symbol 'environ'
>> in some situations, but not all situations.  I have found a variety of
>> forum posts and mailing list entries on the Internet that describe the
>> problem and how to fix it.  The message
>>
>>  http://lists.apple.com/archives/xcode-users/2004/jan/msg00230.html
>>
>> gives a particularly clear description of the issue and I quote part  
>> of
>> it here:
>>
>>> _environ is defined in /usr/lib/crt1.o, which is only linked into
>>> executables. The corresponding file for dylibs (which frameworks  
>>> use) is
>>> /usr/lib/dylib1.o and doesn't define _environ. Annoying as that is,  
>>> it's
>>> correct because otherwise your library's _environ would be different 
>>> from
>>> the _environ of the executable that loaded it.
>>>
>>> If you want to use _environ in a library on Mac OS X, you should use
>>> *_NSGetEnviron() instead. It's defined in /usr/include/crt_externs.h.
>>>
>>> Hope this helps,
>>> Eric
>>
>> As far as I can tell, the only place in EPICS base that uses the  
>> 'environ'
>> symbol is the function epicsEnvShow() in "src/libCom/osi/os/default/ 
>> osdEnv.c"
>> I have created a modified version of this function that looks like  
>> this
>>
>>  #if defined(__APPLE__)
>>  #  include <crt_externs.h>
>>  #  define environ (*_NSGetEnviron())
>>  #endif
>>
>>  /*
>>   * Show the value of the specified, or all, environment variables
>>   */
>>  epicsShareFunc void epicsShareAPI epicsEnvShow (const char *name)
>>  {
>>      if (name == NULL) {
>>
>>  #if !defined(__APPLE__)
>>          extern char **environ;
>>  #endif
>>
>>          char **sp;
>>
>>          for (sp = environ ; (sp != NULL) && (*sp != NULL) ; sp++)
>>              printf ("%s\n", *sp);
>>      }
>>      else {
>>          const char *cp = getenv (name);
>>          if (cp == NULL)
>>              printf ("%s is not an environment variable.\n", name);
>>          else
>>              printf ("%s=%s\n", name, cp);
>>      }
>>  }
>>
>> I haven't actually tested the modified version of the function, since I
>> do not use epicsEnvShow() for anything, but this change is enough to  
>> get
>> my Python module to load successfully without any missing symbols.
>>
>> Hope this helps,
>>
>> Bill Lavender
>>
>
> -- 
> Eric Norum <norume@aps.anl.gov>
> Advanced Photon Source
> Argonne National Laboratory
> (630) 252-4793
>
>