why don't automake and autotools lose power of GNU Make?

Question

I am very experienced with GNU Make but a complete stranger to autotools. From looking at some tutorials, I understand that autotools are a way to standardize makefile targets and builds across multiple architectures. Which is a good thing, so the user of open-source distributions, can always build and install them in the same way.

GNU Make is very powerful and flexible: any shell command can be used to build targets and dependencies of targets on prerequisites can be expressed in many efficient and flexible ways.

Can all the power of a Makefile be transferred to automake-based system by turning the Makefile into Makefile.am ? I found statements in tutorials such as:

rules like

%.foo: %.bar

are not portable and cannot be used in Makefile.am . As such, the programmer would have to write explicit rules where pattern rules suffice, which is definitely more time consuming and less maintainable.

Also, I never see any complex variable computations or functions, in the example Makefile.am files I have seen.

Then how can automake build the same software with the same efficiency, speed of programming and maintainability as GNU Make, if it restricts the GNU Make constructs?

I assume it can, I just don't see something obvious.

Answer 1

I'm not very proficient in, nor a big fan of the autotools, but my understanding is this:

The purpose of the autotools was to improve portability, for example to systems that didn't have GNU Make available. Examples included HP-UX, Solaris, IRIX and the BSD family. The autotools users could build programs with an always-constant sequence of instructions:

./configure
make

Here, ./configure is a /bin/sh script that is generated on the developer's system and is portable so it can run on a wide range of systems. The generated Makefile was platform-specific and included handling for platform-specific requirements/issues. Also, ./configure generates a config.h file which allows C code to react to the availability/absence of certain libraries to build options passed to ./configure.

The Wikipedia page on GNU build system includes a nice diagram of the files involved in the whole process:

Everything up to configure and Makefile.in is pre-generated on the developer system, config.status and below are generated on the build (user) system.

What is the relevance of the autotools today? Obviously, they are still used in many projects. However, the importance of non-Linux UNIX operating systems has dropped tremendously. Those that do still exist all have GNU Make available. As you said, GNU Make has an astonishing number of features and makes it very easy to write Makefiles that automatically track dependencies and handle available/missing libraries.

Thus, I personally write all my make systems based on GNU Make and I'm happy that I haven't had to touch the autotools in years.