Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Tue, 18 Jul 2017 18:25:43 +0200

On 05.10.2016 21:48, Andrew Johnson wrote:
> Before she retired Janet Anderson was working on an alternative approach
> for Unix-like systems using $ORIGIN in the RPATH, but that wasn't
> working out very well when you have multiple modules installed in
> different locations. $ORIGIN lets you embed a search path for shared
> libraries that is relative to the current location of the binary executable.

We are using this approach since quite some time for our IOC
applications. Our solution to the problem you mention above
("...multiple modules installed in different locations...") is perhaps
crude but works well in practice: the final application pulls in copies
of the shared libraries of all used modules (placing them under
INSTALL_BIN), and sets the RPATH to $ORIGIN, as in:

TOP=..
include $(TOP)/configure/CONFIG
#----------------------------------------
#  ADD MACRO DEFINITIONS AFTER THIS LINE

MODULE_PATHS = $(SHRLIB_SEARCH_DIRS)
MODULE_LIBNAMES = $(notdir $(foreach dir,$(MODULE_PATHS),$(wildcard
$(dir)/lib*.a)))
MODULE_NAMES = $(MODULE_LIBNAMES:$(LIB_PREFIX)%.a=%)

## Linux

MODULES_Linux = $(foreach dir,$(SHRLIB_SEARCH_DIRS),$(wildcard
$(dir)/lib*.so*))
BIN_INSTALLS_Linux = $(MODULES_Linux)

LINKER_USE_RPATH=NO
USR_LDFLAGS += '-Wl,-rpath,$ORIGIN'

PROD_Linux += ...

include $(TOP)/configure/RULES
#----------------------------------------
#  ADD RULES AFTER THIS LINE

(In fact, since our build machine runs Debian 7 which, unfortunately,
has a broken linker that does not properly handle $ORIGIN, the above
doesn't work for us, so instead what we actually do is

USR_LDFLAGS += '-Wl,-rpath,../../bin/$(T_A)'

which relies on the IOC being started from inside the location of its
startup script...)

One might think that copying all the shared libraries is inefficient. It
turns out that the overhead of the EPICS build system with its recursive
make invocations, plus execution of our own build rules which heavily
depend on perl and python scripts to generate db files and other stuff,
completely dwarfs the mere copying of a few megabytes.

One advantage of doing it this way is that we never rely on distributing
build results for support modules: only the final application that
builds the IOCs distributes stuff (to the host that runs the IOC). This
means that dependencies (except for system libraries) are fully handled
on the build machine.

Furthermore, our method of distribution is such that unchanged files
will not be transferred but merely hard-linked to an existing version on
the target side, so the pulled-in .so files will only rarely be moved
over the network at all (in fact only once when the application switches
to a new version of the module) and take up almost no extra space. In
fact, we have chosen this method in part because it greatly speeds up
distribution.

Cheers
Ben
-- 
"Make it so they have to reboot after every typo." ― Scott Adams

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System