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Subject:	Re: Problem with dlsym against libicu
To:	cygwin AT cygwin DOT com
References:	<CABHT963DoTimY9woRrF_kcBSEeUhN2ONhrnnPFL-9CAmDt5geA AT mail DOT gmail DOT com>
From:	Ken Brown <kbrown AT cornell DOT edu>
Message-ID:	<56A39A8D.5050807@cornell.edu>
Date:	Sat, 23 Jan 2016 10:21:49 -0500
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On 1/22/2016 10:49 PM, Sam Habiel wrote:
> Hello all.
>
> I am porting GT.M
> (https://www.fisglobal.com/Solutions/Services/Database-Engine) to run
> on Cygwin x86. My changes are here:
> https://github.com/shabiel/fis-gtm/. GT.M is used in healthcare and
> banking; I happen to work in the former field.
>
> The problem I am having is that GT.M opens libicuio via dlopen, and
> then loads the function pointers into a data structure via function
> name using dlsym. For the curious, the code is in gtm_icu_init() in
> gtc_icu.c
>
> I took me a while, but I eventually figured out that dlls that are
> opened via dlopen need to be in the PATH in Cygwin. I saw this in an
> earlier Cygwin mailing list message.
>
> However, no matter what I do, I can't seem to get a non-null reference
> to a named symbol in libicuio via dlsym. Here's what I tried:
>
> 0. nm shows the symbols in the file I want to open; strace shows me
> opening it (it's /usr/lib/cygicuio56.dll).
> 1. Compiled libicu from source with a flag for Cygwin:
> http://site.icu-project.org/
> 2. Used underscores in front of the symbol
> 3. Tried creating an import library using the instructions at
> https://cygwin.com/cygwin-ug-net/dll.html#dll-build at the bottom and
> then add the archive to the gcc compile command as a source file.
> (These instructions need to be improved! I had no idea what to do with
> a .a file after I got it).
>
> Here's a test program that I have written. Note that dlsym returns the
> obscure error message "no such process", which doesn't make any sense
> to me, as I am not looking for a "process" but a symbol.
>
> sam AT horus ~/fis-gtm-cygwin
> $ cat test.c
> #include <dlfcn.h>
> #include <stdio.h>
> #include <stdlib.h>
>
>
> int main (int arg, char **argv)
> {
>      void *ptr = dlopen("cygicuio.dll", RTLD_LAZY);
>      if (ptr != NULL)
>      {
>          printf("%p\n",ptr);
>      }
>      else
>      {
>          printf("%s",dlerror());
>          exit(1);
>      }
>
>      void *ptr2 = dlsym(ptr,"uset_open");
>
>      if (ptr2 != NULL)
>      {
>          printf("%p\n",ptr2);
>      }
>      else
>      {
>          printf("%s",dlerror());
>          exit(1);
>      }
>
>      return 0;
> }

I can't answer your questions, but I have some comments and questions.

First, there's no /usr/lib/cygicuio56.dll in the Cygwin icu 
distribution.  The DLL is /usr/bin/cygicuio56.dll, with the 
corresponding import library /usr/lib/libicuio56.dll.a (provided by the 
libicu-devel-56.1 package).  And there's also a symlink 
/usr/lib/libicuio.dll.a -> libicuio56.dll.a.

Next, can you show the nm command by which you found uset_open?  I 
couldn't find it.  I tried

$ nm /usr/lib/libicuio56.dll.a | grep uset_open

and got nothing.  On the other hand:

$ strings /usr/bin/cygicuio56.dll | grep uset_open
uset_open_56

Could the problem be that uset_open (or uset_open_56) isn't exported?

Ken

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