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+ The Myrddin Compiler Build System
+ Aug 2012
+ Ori Bernstein
+
+TABLE OF CONTENTS:
+
+ 0. DEPENDENCIES
+ 1. USAGE
+ 2. CREATING MAKEFILES
+ 2.1. Example
+ 2.2. Targets
+ 2.3. Variables
+ 3. CONFIGURE SCRIPTS
+ 4. INTERNALS
+ 4.1: Automatic dependency generation
+ 4.2: Automatic dependency generation
+ 4. BUGS
+
+0. DEPENDENCIES:
+
+ c.mk depends on GNU Make, using it's builtins for a
+ number of variable expansions. On systems where the default make
+ program is not GNU Make, please run 'gmake' or similar. Otherwise,
+ you will end up with obscure failures. A method of making this
+ script portable would be very welcome.
+
+ Beyond that, all that is needed to run this is a portable POSIX
+ system.
+
+1. USAGE:
+
+ run 'make' and the default targets will be built. The usual targets
+ are supported. That means:
+
+ all:
+ Builds all targets. This will build every target
+ specified in the makefile, recurse into subdirectories,
+ and do everything needed. If dependencies are in other
+ directories, it will 'cd' into those directories and
+ call make as needed.
+
+ target-name:
+ This builds the specified target and it's dependencies.
+
+ install:
+ This installs the software to the prefix specified in the
+ configuration, or /usr/local if there is nothing more
+ specific specified.
+
+ If DESTDIR is set, it will install the files to the prefix
+ $(DESTDIR)/$(INST_ROOT), although all paths will still be
+ relative to $(INST_ROOT). This is for packaging, and matches
+ the behavior of automake.
+
+ uninstall:
+ This uninstalls the software, removing all files installed
+ by 'make install'.
+
+ clean:
+ This removes all temporary files created by the build
+ process, allowing a fresh build to occur.
+
+ When a target is not specified, 'all' is assumed.
+
+2. CREATING MAKEFILES:
+
+ c.mk is only a set of rules to make common actions simple. There is
+ nothing preventing custom make from being added for
+
+ 2.1: Example
+
+ c.mk is designed around the convention of having
+ one primary target per directory. This primary target can be
+ either a binary or a library, for the most part, although
+ there is nothing that prevents you from defining your own
+ primary targets.
+
+ So, let's dissect an example makefile:
+
+ BIN = mybinary
+ INSTBIN = $(BIN)
+ OBJ = foo.o bar.o baz.o
+
+ include config.mk
+ include c.mk
+
+ custom-rule: custom-dep
+ insult-your-momma
+
+ 2.2: Targets
+
+ Currently, there are several targets supported by c.mk
+
+ SUB
+ This target will recurse into the subdirectories
+ listed, building everything in them.
+
+ BIN
+ This target will build a single binary, and will
+ not install it. It uses $(OBJ) as its input.
+
+ LIB
+ This target will build a single static library, and will
+ not install it. It uses $(OBJ) as its input. It
+ conflicts with $(BIN)
+
+ INSTBIN
+ Same as BIN, but installed to $(INST_ROOT)/bin
+
+ INSTLIB
+ Same as LIB, but installed to $(INST_ROOT)/lib
+
+ INSTHDR
+ Used for defining headers to install to system include
+ directories. Does not generate headers. Takes multiple
+ arguments and installs them to $(INST_ROOT)/include
+
+ INSTPKG
+ Used for defining pkgconfig files to install to
+ system pkgconfig directories. Does not generate
+ them from inputs. Takes multiple arguments and
+ installs them to $(INST_ROOT)/lib/pkgconfig.
+
+ INSTMAN
+ Used for defining manpage files to install to
+ system man directories. Does not generate
+ them from inputs. Takes multiple arguments and
+ installs them to $(INST_ROOT)/lib/pkgconfig.
+
+ 2.3: Variables:
+
+ c.mk respects the usual environment variables. If you set
+ CFLAGS, it will compile with those flags. If you set LDFLAGS,
+ it will link with those flags. It also supports a number of
+ extra configuration variables:
+
+ EXTRA
+ Dependencies that should be built when 'make all' is
+ run. These can be, for example, additional binaries,
+ rules, etc.
+
+ EXTRADEP
+ Dependencies that should be added when compiling a
+ BIN or LIB target
+
+ GENHDR
+ Headers that are generated for consumption by C code.
+
+ CLEAN
+ Files that should be removed when runngng
+
+ INCS
+ Include paths. These are passed to the C compiler when
+ building C code.
+
+ DEPS
+ Paths to local dependencies, such as convenience
+ libraries. This is a relative path to a libfoo.a
+ file. All libraries that are depended on in this
+ manner will be automatically built before they
+ are used.
+
+ The path to them will also be added to the include
+ path if needed, and they will be linked in to binaries
+ that are built.
+
+3. CONFIGURE SCRIPTS:
+
+ This is not mandatory, although convention requests it. This is
+ simply a shell script that will probe the system, and generate
+ the 'config.mk' file, This can be generated a number of ways.
+
+ Although Myrddin doesn't currently use it, autoconf is a perfectly
+ viable method of generating a config.mk setup. Myrddin currently
+ uses a simple script that mocks autotools, instead.
+
+4. INTERNALS:
+
+ c.mk is a relatively simple set of commands. It defines make targets
+ for the various default rules, and uses the variables described
+ above to substitute into them, with fairly traditional structure.
+
+ It begins by setting the default goal (ie, the target that is built
+ when 'make' is run with no arguments) to 'all', and proceeds to
+ define a few internal variables.
+
+ 4.1: Automatic dependency generation
+
+ _DEPSDIR and _DEPS are defined early on. _DEPSDIR is simply
+ a directory named '.deps', which is created before any
+ compilation occurs, and contains the dependency makefile
+ fragments that GCC generates.
+
+ _DEPS is the list of dependency filename fragments, generated
+ by substituting '.deps/$FILEBASE.d' for every .o file define
+ in $(OBJS)
+
+ CFLAGS also unconditionally has the required flags for
+ dependency generation added to the compiler command, and
+ later on, the dependencies are included into the makefile
+ if they exist.
+
+ 4.2:
+
+ The general target rules are defined. There are many for
+ loops and bits of shell scripting to support them, but the
+ pattern is fairly basic.
+
+ well-known-target: prerequisites
+ do-commands
+
+ Some of the commands are fairly long. For example, the install
+ and uninstall targets will loop through a list of files for each
+ of the main target types.
+
+ is simply '.deps', and is the location where GCC's generated
+ dependency information goes. _DEPS
+
+4. BUGS:
+
+ - Currently, 'make uninstall' does not remove empty directories that
+ it created.
+
+ - You can define BIN/INSTBIN, LIB/INSTLIB in a way that does not
+ match. We do not error on this.
+
+ - Well known targets are defined relatively inflexibly. It should
+ be easier to include modules and have them add on to the base
+ rule set.