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Message-ID:	<CABHT963DoTimY9woRrF_kcBSEeUhN2ONhrnnPFL-9CAmDt5geA@mail.gmail.com>
Subject:	Problem with dlsym against libicu
From:	Sam Habiel <sam DOT habiel AT gmail DOT com>
To:	cygwin AT cygwin DOT com
X-IsSubscribed:	yes

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;
}

sam AT horus ~/fis-gtm-cygwin
$ gcc -Wall -otest.o test.c

sam AT horus ~/fis-gtm-cygwin
$ ./test.o
No such file or directory
sam AT horus ~/fis-gtm-cygwin
$ PATH=/usr/lib:/usr/bin:/usr/local/bin:. ./test.o
0x6aa40000
No such process
sam AT horus ~/fis-gtm-cygwin

-- 
Sam Habiel, Pharm.D.
VISTA Expertise Network

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