gnustep-make-2.8.0/Documentation/DESIGN

[Important: this is mostly a historical document.]

A makefile package for the GNUstep environment
==============================================

This document presents a makefile package for the GNUstep
environment. It describes what are the goals the GNUstep environment
should achieve and then presents some solutions.

Goals
=====

There are several issues we tried to solve while designing a directory
structure and the configuration/make procedures required to build a
package.

We tried to define a directory structure for keeping all the GNUstep
related files. This structure makes the things more consistent and the
configuration and compile process of various GNUstep packages more
easier.

An important issue is to let to a package the ability to deal with
various libraries and configurations available now:

* different Objective-C runtimes. In the Objective-C world there are
currently two major runtimes: the NeXT runtime and the GNU
runtime. They are different in several respects and a program or
library that works at the runtime level should be aware of them.

* different Foundation libraries. There are several Foundation libraries
an OpenStep application can be written on top of: NeXT Foundation
library which runs on NeXTStep/OPENSTEP systems, PDO (Portable
Distributed Objects) which runs on a variety of Unix systems,
gnustep-base and libFoundation.

* different graphical interfaces. Until now two libraries provide or
try to provide OpenStep compliant systems: the AppKit from NeXT and
the GNUstep graphical libraries.

The makefile package should be a simplistic, powerful and extensible
way to write makefiles for a GNUstep project. It should allow the user
to easily specify a library combination he/she wants to use when
compiling a project. Also it should allow the user to easily create
cross-compiled binaries.

Library combinations
====================

If an application wants to work with all the possible combinations it
will have to provide different binaries for each combination because
it's not possible to have an application compiled for NeXT PDO that
runs with gnustep-base or vice-versa. To summarize, an application can
be compiled for these combinations:

Objective-C runtime: NeXT, GNU
Foundation library: NeXT, PDO, gnustep-base, libFoundation
GUI library: NeXT, gnustep-gui

Objective-C runtime: nx (for NeXT), gnu (for GNU)
Foundation library: nx (for NeXT), pdo (for PDO), gnu (for gnustep-base),
		fd (for libFoundation)
GUI library: nx (for NeXT), gnu (for gnustep-gui)

We'll denote the fact that an application was compiled for a certain
combination of the above values by using the abbreviations of the
different subsystems and placing dashes between them. For example
an application compiled for NeXT Foundation using NeXT AppKit will
have the compile attribute nx-nx-nx. An application compiled for
PDO with the gnustep-gui library under Unix will be denoted by
nx-pdo-gnu and another one compiled for gnustep-base using
gnustep-gui under Unix will be denoted by gnu-gnu-gnu. Here is a
list of some of the possible combinations:

ObjC runtime	Foundation	GUI
------------	----------	---
    nx		    nx		nx
    nx		    pdo		nx
    nx		    pdo		gnu
    gnu		    gnu		gnu
    gnu		    gnu		gnu
    nx		    fd		gnu
    gnu		    fd		gnu

Note that one can choose his/her own packages to build; it is not
required to have all the packages installed on the system. Not having
all of them installed limits only the ability to build and distribute
binaries for those missing combinations.

Directory structure
===================

There are several directories used in a GNUstep environment. The
directories are relative to a top directory whose name is given by the
variable GNUSTEP_SYSTEM_ROOT ($GNUSTEP_SYSTEM_ROOT in a shell or
$(GNUSTEP_SYSTEM_ROOT) in a makefile). Below is the hierarchy of
GNUstep directories:

$(GNUSTEP_SYSTEM_ROOT)/
    Headers/
    Libraries/
    Applications/
    Tools/

The Headers/ and Libraries/ directories, as their names suggest, keep
the header files and the libraries required by a GNUstep project to
compile and link. The libraries can be both shared or static,
depending on the target system.

The Applications/ directory is used by GNUstep graphical applications,
those applications which have a graphical interface with the user. The
Tools/ directory holds command line tools based on GNUstep libraries.

The header files are grouped like this in the Headers/ directory:

Headers/
  gnustep/
    base/
    Foundation -> base
    gui/
    AppKit -> gui
  libFoundation/
    Foundation/

The Libraries/ directory can hold libraries for several machines and
several combinations of packages:

Libraries/
  i386/
    linux-gnu/
      gnu-gnu-gnu/
	libgnustep-base.so
	libgnustep-gui.so
      gnu-fd-gnu/
	libFoundation.so
	libgnustep-gui.so
  sparc/
    solaris-2.5.1/
      nx-pdo-gnu/
	libgnustep-gui.so

Please note that the Libraries/ directory contains only the libraries
that come with GNUstep, the PDO library for example is not inside
Libraries/. The compiler has to know where that library can be found,
although the makefile package is responsible for passing all the
necessary flags during compiling and linking.

The libraries directory also contains resource files which belong to
the GNUstep libraries, such as images and printer description
files. Since the images can look different for different backends,
each backend has its own images in a different directory based upon
the interface look and feel:

Libraries/
  Resources/
    Images/
      NeXT/
      Win32/
    PrinterTypes/
    Fonts/
    gnustep/
	NSCharacterSets/
    libFoundation/
      CharacterSets/
      Defaults/
      TimeZoneInfo/

The resources that are specific to each Foundation libraries are kept
in a subdirectory like above, except for NeXT Foundation and PDO which
keep their resources in their own places.

The Applications/ directory contains GNUstep graphical
applications. Each application is kept in an app wrapper which
contains all the binaries and all the resource files the application
needs. The binaries organization resembles the one from libraries:

Applications/
  InterfaceModeller.app/
    InterfaceModeller (for OPENSTEP systems compatibility)
    i386/
      linux-gnu/
	gnu-gnu-gnu/
	  InterfaceModeller
    sparc/
      solaris-2.5.1/
	nx-pdo-gnu/
	  InterfaceModeller

The Tools/ directory contains command line tools.  Each tool
executable is placed in a subdirectory corresponding to the CPU and
operating system.

Tools/
  i386/
    linux-gnu/
	autoconf
	gcc
	dgs
  sparc/
    solaris-2.5.1/
	autoconf
	gcc


The makefile package
====================

The GNUstep environment needs a makefile package whose purpose is to
simplify writing a GNUstep project. This package should help
developers easily write makefiles for compiling their projects.

Theoretically an OpenStep application should only use OpenStep API, it
should not rely at all on system specific header files. This is the
most portable way to write an OpenStep application. For this kind of
applications configuring is not necessary since no system specific
header files or libraries need to be checked. The idea is to try
eliminate the configuring process because of the problems it has in
the presence of cross-compiling. Not relying on system files in a
GNUstep project means that you don't need to check for them, so the
project can simply be compiled by just typing `make'.

This is the best scenario for a GNUstep package. If configuring is
still needed the makefile package should support it without major
changes.

We identified until now the following types of projects:

- application: for projects whose result are graphical GNUstep applications
- tool: for command line programs which use GNUstep libraries
- library: for creating libraries (both static and shared)
- bundle: for creating a dynamically loaded bundle
- aggregate: for projects that contain several other subprojects like
  libraries, bundles and so on

Another possible type of project could be "pallete", for adding
functionality to the GNUstep InterfaceModeller application. Other
project types can be added as well, the makefile package does not
limit this in any way.

A project consists from a collection of source code files and resource
files. If a project has several subdirectories, those subdirectories
are subprojects of the main project. A subproject type is not
restricted in any way by the type of the project it's contained
into. The only restriction is that you can not create multiple project
types from the files in the same directory.

For a project that does not need any additional configuring before
compiling the only thing required to build the project should be
typing

  $ make

in the command line :-).

Where the object files go
=========================

The object files will go in a separate directory identified by the
name of the target system and of the development environment used
(ObjC runtime, Foundation library and GUI libraries). This way one can
use the same source tree for building the project for multiple
targets.

How to choose the library combination
=====================================

The makefile package will allow the user to choose between different
library combinations. To specify a combination you want to compile for
just type:

  $ make library_combo="library combination"

For instance if you want to choose to compile using the NeXT's PDO
Foundation and use the GNUstep GUI library on a Unix machine you can
do like this:

  $ make library_combo=nx-pdo-gnu


Projects that require running configure before compiling
========================================================

There are two issues with this kind of projects. 'configure' is used
to determine the existence of particular header files and/or of some
specific functionality in the system header files. This thing is
usually done by creating a config.h file which contains a couple of
defines like HAVE_... which say if the checked functionality is
present or not.

Another usage of configure is to determine some specific libraries to
link against to and/or some specific tools. A typical GNUstep program
is not required to check for additional libraries because this step is
done by the time the makefile package is installed. If the project
still needs to check for additional libraries and/or tools, the
recommended way is to output a config.mak file which is included by
the main makefile, instead of using Makefile.in files which are
modified by configure. The reason for not doing this is to avoid
having the Makefiles contain target dependencies like above, this way
keeping only one makefile instead of several for each target machine.

The makefile package will be written for GNU make because it provides
some very powerful features that save time both in writing the package
but also at runtime, when you compile a project.

How to build a package for different architectures
==================================================

In order to build a project for multiple architectures you'll need the
development environment for the target machine installed on your
machine. This includes a cross-compiler together with all the
additional tools like the assembler and linker, the target header
files and all the libraries you need.

The GNUstep makefile package should be able to compile and link an
application for another machine just by typing

  $ make target="target machine"

where "target machine" is the canonical system name as reported by
config.guess.

Building different types of a project
=====================================

During development you usually need to switch between a debug version and a
profile one without having to recompile all of the sources. The makefile
package allows you to do this by letting you define three boolean make
variables. The values of these variables can be either "yes" or "no".

* debug

If the value is yes then it is assumed that the target is to be built with
debugging info. By default the optimization is turned on but you can control
this behavior via the OPTFLAGS make variable. The default is no.

* shared

It makes sense to specify this only for library targets. This variable says
if the target needs to be built as a shared library. On systems that support
shared libraries this is the default; the user has to explicitly specify
shared=no in the command line.

* profile

When this variable is yes, a profile version of the target is built. The
default is no.

For example if you want to build a shared library with debug information
enabled but no profile information, the command line would be:

  $ make shared=yes debug=yes profile=no

The last argument is not necessary because the default is to build a version
without profile information.

The object files will be output into the shared_debug_obj directory. If the
profile is turned on the output directory would be shared_profile_debug_obj.

Of course you also have to specify the library combo if it's different than the
default.

Naming conventions of the libraries
===================================

Sometimes you need to have different versions of a library compiled with
different options. Suppose you want to compile a library with profiling
information enabled so that you can profile your code. But you don't want to
overwrite your existing installed library so that only some of the applications
will work with the profile library, the rest will still use the normal library.

The makefile package supports such a schema by having different names for
different types of the same library. This works by appending an underscore
after the name of the library followed by a letter which indicates the type of
the library:

's' for a static library
'p' for a profile library
'd' for a debug library

So for example if you have the library 'example' compiled with debug
information as a shared library it would be named libexample_d.so. If the same
library is compiled as a static library its name would be named
libexample_sd.a. The reason why the 's' letter for the static library appears
in name of the library is for systems where the extensions of libraries don't
matter.

It is possible to compile a library with whatever combination of flags you
want. The letters are appended in the order specified above, so if you compile
the library as a static library, with profile and debug information enabled,
the library name will have the _spd suffix appended.

How a library is chosen
=======================

What happens if you compile an application with profile enabled and you don't
have a library compiled with profile info into it, but you do have a normal
library installed? It would be great if the normal library is chosen instead.
This is a problem because the library that should be chosen has a different
name than the profile library.

We do support this schema by requiring the libraries to be specified using the
short name, without any suffix appended to it. The `example' library in our
case should be passed to the linker using -lexample, and not using -lexample_p.
Based upon the shared, profile and debug variables, the makefile package will
identify which are the libraries that exist on the system and it will come with
the correct names when linking.

The search order of libraries depending on what type of library is required is
as follows. First of all an exact match is searched; if one is found it is
returned. If either debug or profile are required, a library that matches at
least one of these attributes is returned. For example if there is a
profile+debug version of a library but only debug is required this library will
match. If a static version is required but no static versions of the library
exist, then no library is chosen; in this case the system simply prints out the
name of the library, assuming a static library is somewhere else in the
libraries search path of the linker.

Building applications
=====================

In the makefile's package terminology an application is a program linked
against the GUI libraries.

An application is built as usualy, by compiling all of the sources and then
linking the object files into the binary. The only difference between
an application and any other project results is that the first is created into
its own directory, instead of being a simple file. This directory is called
the application wrapper and it contains the binaries for various architectures
and resources needed by the application.

The name of the application wrapper is taken to be the name of the application
with the following extensions:

.profile - if the application has been built with profile enabled
.debug - if the application has been built with debug enabled
.app - if the application has been built without debug or profile enabled

If both debug and profile are enabled, the application extension will simply
have the .profile extension. This is different from libraries were both options
are reflected into the library's name.

The structure of makefiles
==========================

The makefile package should be built so that a user project will only
have to define what are the Objective-C files he/she uses, what are
the C files, the header files and so on. All the rules that know how
to build a library, an application or whatever type of project are
defined in the internal files of the makefile package.

This organization has several advantages. The main advantage is that
we keep the makefiles in a GNUstep project small, only the makefile
variable definitions. The other advantage is that all the build
knowledge is centralized in a single place, the makefile
package. Right now each GNUstep package tries to solve all of the
issues related to the package building and nothing is reusable.

The way the main makefile of a project should be written requires the
user to specify the files needed by the make process and what kind of
project needs to be built. This is defined by including a certain
makefile package file. For example if the package to be built is an
application then a possible Makefile can look like this:

APP_NAME = test1 test2
test1_OBJC_FILES = test1.m
test2_OBJC_FILES = test2.m test21.m

-include Makefile.preamble
include application.make
-include Makefile.postamble


The main makefile will be generated automatically in the future by the
ProjectCenter. This presents problems if the user wants to add his/her
own makefiles targets or additional rules. Two additional files are
provided: Makefile.preamble and Makefile.postamble. The first file is
included before the makefile for the specific project type and is
intended for redefining the standard variables or for adding to
them. The second one is intended for adding additional rules or
targets.

The makefile package is installed under $(GNUSTEP_SYSTEM_ROOT)/Library/Makefiles.


Ovidiu Predescu

Last updated: April, 2001