Experimental Physics and
Industrial Control System

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From: Janet Anderson [mailto:[email protected]]
Sent: Tuesday, July 17, 2007 1:48 PM
To: Mark Rivers
Cc: Andrew Johnson; EPICS tech-talk
Subject: Re: Asyn 4.8 compile error with Linux GPIB

The difference between SYS_LIBS and LIBS is that users don't have to provide
a  <libname>_DIR in the Makefile for SYS_LIBS libraries and the build rules dont
try to create an -L<dirname>  option for SYS_LIBS libraries. A SYS_LIBS library
is assumed to reside in one of the linker's default library search paths.

Janet



Mark Rivers wrote:

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