Experimental Physics and
Industrial Control System

"Mark Rivers" <[email protected]> · Tue, 17 Jul 2007 11:47:56 -0500

The Application Developer's Guide does not explain the difference
between asyn_LIBS and asyn_SYS_LIBS, except for the order in which they
are passed to the linker.  What is the difference?  I have always used
SYS_LIBS for libraries that are not in the EPICS directories.  I think
one difference is that when building a static application that shareable
versions of SYS_LIBS are still used, while all non SYS_LIBS libraries
are statically built into the binary, right?  Is this documented
anywhere?

Mark

> -----Original Message-----
> From: Andrew Johnson [mailto:[email protected]] 
> Sent: Tuesday, July 17, 2007 10:49 AM
> To: Mark Rivers
> Cc: Jiro Fujita; EPICS tech-talk
> Subject: Re: RE: Asyn 4.8 compile error with Linux GPIB
> 
> Hi Mark,
> 
> > The line 
> > 
> > asyn_LIBS += gpib
> > 
> > tells the EPICS build system to look for libgpib.a in the EPICS 
> > directories.  This does not seem to be correct, that is a system 
> > library, not an EPICS library.  So I think that line should be
> 
> No, setting asyn_LIBS like that tells the build system to 
> link the asyn binary with libgpib (it results in the link 
> line having -lgpib added to it). If libgpib is not being 
> found you can explicitly tell the build system where it is by 
> setting the gpib_DIR variable in the Makefile.  Alternatively 
> and more generally you can tell the linker to look in 
> /usr/local/lib automatically by listing that directory in 
> /etc/ld.so.conf or by creating a file in /etc/ld.so.com.d 
> with the appropriate setting.
> 
> > Note, I think that LD_LIBRARY_PATH is used only at run-time to find 
> > .so files, not when building applications, so I would not expect it 
> > to work.  
> 
> Sorry, but you're wrong there too; having LD_LIBRARY_PATH set 
> at build-time is actually frowned upon nowadays because if 
> it's set at link time its value will be saved in the binary 
> and the path re-used at runtime, which is contrary to how 
> most Linux package management systems like to work (they 
> build in a different location to their final runtime 
> location, so their link-time paths will not be valid at runtime).
> 
> > I don't think you have explained how libgpib.a got in the asyn 
> > tree, if it really is there.
> 
> I agree, I think that file should be deleted.
> 
> - Andrew
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System