Re: build configuration help

[John Calcote]

Bob Rossi wrote:
> If I put it in the lib directory on other platforms, on startup, how
> will the binary know where to find the .so? That's why I was asking
> about LD_LIBRARY_PATH, and creating a script....
>   
Okay, let me ask a few questions to clarify your situation. First, is 
this library being loaded by the linker at runtime, or is it dynamically 
loaded by your application, using dlopen/dlsym/dlclose (Linux), or 
LoadLibrary/GetProcAddress/FreeLibrary (Win32)?

On Unix systems the "library path" is configured in your application, 
and in the system. Libraries are searched for (in general) in the system 
linker cache, which by default contains (at least) 
"/usr/local/lib:/usr/lib:/lib", as well as others in most cases. If your 
library is being loaded by the system at app init time, then it should 
have no trouble finding your library if it's installed in one of these 
two places. Here's some text I copied (shamelessly) from the ld man page:

          The linker uses the following search paths to locate required 
shared libraries.

          1.  Any directories specified by -rpath-link options.

          2.  Any  directories  specified  by -rpath options.  The 
difference between
               -rpath and -rpath-link is that directories specified by 
-rpath options are
                included in the executable and used  at  runtime,  
whereas the -rpath-link
                option is only effective at link time. It is for the 
native linker only.

          3.  On  an  ELF  system,  if the -rpath and "rpath-link" 
options were not
                used, search the contents of the environment variable 
"LD_RUN_PATH".
                It is for the native linker only.

          4.  On SunOS, if the -rpath option was not used, search any 
directories
               specified using -L options.

          5.  For a native linker, the contents of the environment variable
               "LD_LIBRARY_PATH".

          6.  For a native ELF linker, the directories in  "DT_RUNPATH"  or
               "DT_RPATH" of  a  shared  library  are searched for 
shared libraries
               needed by it. The "DT_RPATH" entries are ignored if 
"DT_RUNPATH"
               entries exist.

          7.  The default directories, normally /lib and /usr/lib.

          8.  For a native linker on an ELF system, if the file 
/etc/ld.so.conf  exists,  the
               list  of  directories found in that file.

If you're linking dynamically at runtime using the dlopen/dlsym/dlclose 
functions, then you can use some of these mechnisms yourself to find 
your library, plus, often an application will allow configuration in a 
.conf file to allow the administrator to configure where the app should 
look for libraries.

So you see, the search algorithms are similar on Unix and Windows 
systems - they just look in different places. Windows treats libraries 
like binaries, so expects to find them in the executable path, while 
Unix treats them as separate first-class entities. They have their own 
search paths, separate from binaries, plus about half a dozen other ways 
to find libraries - some system-configured, and others hard-coded into 
your app by the linker. But none of these methods look in the bin 
directory for a library.

John