Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Thu, 22 Dec 2005 05:19:25 +0100

On Wednesday 21 December 2005 18:34, Emmanuel Mayssat wrote:
> The build system is quite frustrating for new comers.
> The makefile includes files which themselves include other files.

And so on. However, this is something that is hard to avoid, due to the 
sheer number of supported host and target systems, compilers, etc. It's 
a combinatorial explosion which can only be tamed by aggressive 
(re-)factoring. This tends to lead to a lot of separate files and many 
complex and strangely nested make variable definitions.

The one /real/ weakness of EPICS' build system is that it (still) 
heavily uses recursive make, with all the by now well-known problems 
this causes, particularly for large applications that consist of many 
inter-dependent modules. (Those problems are due to the artificial 
fragmentation of the dependency graph caused by recursive make).

> So quite tricky to understand the details, specifically when it
> doesn't build.
>
> If you don't want to know about the build system, then we have
> something in common ;-)

I wholeheartedly agree, however...

> My advice to you is that instead of modifying your Makefile, you may
> want to change your environment and use the gmake -e option.
>
> That way you will be able
> 1/ to keep the original files in the base
>       ( very useful if you want to upgrade epics very easily or build
> several base in different directories, etc.)

The standard (=recommended) way to achieve this is to import the sources 
into your own CVS repo, and merge your local changes into new versions.

> 2/ You can keep track of your change

See above. CVS works even better ;-)

> 3/ you can automate the build process in scripts

Well, typing 'make' is as automated as it gets, I'd say. And you'll have 
to maintain those scripts. The Make-System evolves even over minor 
EPICS revisions, some variables may disappear others may be added. Your 
build script inevitably either suffers bit-rot, or gets more and more 
complicated each time you add a new EPICS version to your site. My 
humble opinion is that maintaining shell scripts is even more of a 
nightmare than maintaining makefiles, but YMMV. Oh, and don't assume 
everyone will upgrade their every application to use the latest EPICS 
release as soon as you install it. They won't. They'll tell you that 
it's too long ago since they wrote it, they have more pressing work to 
do, it works fine so why change it etc.etc. unless you /force/ them to 
do it by deleting the old EPICS version and then they'll just hate 
you ;)

Anyway, it was a deliberate decision in the design of the EPICS build 
system to keep every <top> module (application) as self-contained as 
possible. If you avoid deleting, renaming, or moving old versions of 
support modules (including base), and instead always place new versions 
beside old ones, you can build even ancient applications right out of 
the box. Well, that's the theory, at least...

Ben

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System