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Re: Problem with dlsym against libicu


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@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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