LCA: Disintermediating distributions [LWN.net]

LCA: Disintermediating distributions

Posted Feb 6, 2008 23:55 UTC (Wed) by stevenj (subscriber, #421)
In reply to: LCA: Disintermediating distributions by vmole
Parent article: LCA: Disintermediating distributions

There are lots of cases where just following the dang standard is not practical, or not sufficient. For one thing, not all platforms implement the dang standard, and if you don't want to fail completely when this happens you need some workaround. For another thing, in some applications it's extremely useful to support functionality that may not be available on all platforms—for example, SSE instructions or high-resolution timers.

Also, a lot of what autoconf deals with is checking for things in the build environment which essential but not standardized, such as how to link shared libraries. e.g. POSIX threads and OpenMP are two examples of formally standardized libraries that you can depend on, but each compiler and OS has its own command to link with them (see here and here). Or suppose you want to use features from the 1999 ANSI C standard, which has been out for 9 years now but compilers (including gcc) still make you jump through hoops to enable support for it, and of course each compiler has its own hoop (which autoconf will detect).

Also, free-software projects often build upon other projects so as to avoid re-inventing the wheel, and there are lots of extremely useful libraries (from GNU readline to HDF5 to LAPACK to Expat to Boost to...I'm just picking things at random) that are not standardized by any standards body. Part of autoconf's job is to help you detect whether such a library is present and contains the function you want (it may not, e.g. if it is the wrong version).

And heaven help you if you want to link together multiple languages, e.g. you have a C++ program and you want to link Fortran numerical libraries (e.g. LAPACK), without autoconf to help you detect how to do it with your compiler (each one has a different incantation).

Also...well, just look at the autoconf documentation for the variety of kinds of things one has to check for. As I said, there's a reason for its popularity, which extends far beyond "the GNU people"...it fills a real need. People who don't understand what it does are doomed to reinvent it badly.

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LCA: Disintermediating distributions

Posted Feb 7, 2008 0:12 UTC (Thu) by vmole (subscriber, #111) [Link]

I agree that those are all problems that autoconf/libtool/etc. claim to solve. My experience (which is extensive) is that they don't reliably work, and I spend a *LOT* more time figuring out the problem and fixing it than I did with packages that simply ask me to set a few variables in the beginning of the Makefile.

I'd guess that if all you ever work with is Linux, BSD, and possibly Solaris, these tools do work, mostly. OTOH, those are the really easy ones.

LCA: Disintermediating distributions

Posted Feb 7, 2008 0:39 UTC (Thu) by stevenj (subscriber, #421) [Link]

The autoconf developers go to great lengths to support systems beyond Linux and BSD, and it's simply untrue that the tools break on other systems. I personally work on software that has run for years on everything from HPUX to Tru64 to UNICOS to AIX to MinGW using the autotools.

It's true that many people don't know what to do when configure fails. The usual mistake is to start poring over the configure script (which is essentially object code) rather than RTFM. configure --help gives a clue: most problems can be solved by setting an environment variable on the command line with configure LDFLAGS=... or whatever. The most common problems in my experience are due to libraries installed in nonstandard locations, and in this case there's simply no way around requiring the user to tell you where things are (which in autoconf is done by setting LDFLAGS and CPPFLAGS).

It's also true that some programmers misuse autoconf. e.g. even though the autoconf manual strenuously recommends doing feature tests by actually compiling and linking things, autoconf also provides a macro to get a canonical target name (e.g. i386-linux-gnu) and some programmers take the shortcut of explicitly testing this when they shouldn't. The difficulty is that if you are testing for a feature that does not have a built-in autoconf test, writing a portable feature test is hard, especially if you don't have many platforms to test on—but again, I think this is somewhat intrinsic to the problem and is not really autoconf's fault.