ref: b0f3b09fc1b44a8cd0715af65774fe3296b9e016
dir: /doc/buildsys.txt/
The Myrddin Compiler Build System
Aug 2014
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.