This document describes the MutekH build system.

Overview of the build process

The build system takes a build configuration file and compiles the desired kernel together with the application.

The build system takes care of dependencies, file modifications, ... And is still simple to use for the beginner.

Depending on the target architecture, the output file may be an ELF (.out), a plain binary file (.bin), an intel-hex file (.hex) or an object file (.o).

User point of view

Invocation

When building MutekH, several options may be used to change the behavior of the build system. These options are given through variables when calling make, in the form:

$ make VAR1=value1 VAR2=value2

Real build process invocation just need to specify build configuration to use:

# using flat and simple build configuration file
$ make CONF=examples/hello/config_soclib_mipsel

# using sectioned build configuration file
$ make CONF=examples/hello/config BUILD=soclib-mipsel

Main variables

The following option is mandatory:

CONF=

An absolute path to the build configuration file.

The following option may be required depending on build configuration file:

BUILD=

A colon separated list of build section names to consider in the build configuration file.

The following options may be useful:

VERBOSE=1

Prints all the commands executed

The following options are useful when building out of the source tree:

MUTEK_SRC_DIR

An absolute path to the MutekH source tree. This defaults to .

BUILD_DIR

An absolute path to the directory containing the objects and results, this defaults to .

CONF_DIR

An absolute path to the directory containing the .config.* files, this defaults to $(BUILD_DIR)

Make targets

The following targets are available

kernel

This is the default target. It builds the kernel for the specified configuration file.

kernel-het

This target builds multiple kernels for heterogeneous multiprocessors platforms.

clean

This target cleans all the compilation results

The following targets are for informational purposes

showpaths

This prints the modules that will be built, their paths, …

cflags

This prints the flags used for compilation

The following targets are available to get help about configuration.

listconfig

Prints the current configuration as expanded by MutekH build system. It also prints available --- but currently undefined --- configuration tokens.

listallconfig

Prints all the configuration tokens, even the ones incompatible with the current configuration.

showconfig

This prints detailed information about a given configuration token. Token must be specified with TOKEN= variable argument.

See usage below.

Build configuration files

Content

MutekH build configuration files contain tokens defining the kernel we are currently building. They must contain:

• the license for the application, enforcing license compatibility between some kernel parts and your code,
• the target architecture
• the libraries used, and their configurations
• the used drivers
• some global compilation switches (optimization, debugging, …)
• ...

Basic syntax

Syntax is token space value. Tokens begin with CONFIG_. Value may be unspecified thus defaults to defined. e.g.

CONFIG_LICENSE_APP_LGPL

# Platform type
CONFIG_ARCH_EMU

# Processor type
CONFIG_CPU_X86_EMU

# Mutek features
CONFIG_PTHREAD

CONFIG_MUTEK_CONSOLE

# Device drivers
CONFIG_DRIVER_CHAR_EMUTTY

# Code compilation options
CONFIG_COMPILE_DEBUG undefined

...

Most common values are defined and undefined to enable and disables features, but some tokens may need numerical or string values.

Have a look to trunk/mutekh/examples/hello for examples of complete build configuration files.

Help display

To display the list of all available tokens:

$ make CONF=path/to/config_file listconfig
$ make CONF=path/to/config_file listallconfig

To display help about a specific token:

$ make CONF=path/to/config_file showconfig TOKEN=CONFIG_PTHREAD

The MutekH API reference manual describes all available configuration tokens too.

Module declaration

A build configuration file may declare a new module. Modules can be located anywhere outside of the main source tree. We must tell the build system the directory where the configuration lies. The path to the module directory is usually the same as its configuration file:

# New source code module to be compiled
# CONFIG_MODULES name:module_dir
  CONFIG_MODULES hello:$(CONFIGPATH)

Advanced syntax

Basic configuration is really simple. Complex applications or multiple target architectures require maintaining multiple configuration files which can be difficult and annoying. The directives presented here can be used to make things easier.

Build configuration files may contains some directives:

%section pattern [pattern ...]

Start a section which will be conditionaly considered depending on the BUILD variable. pattern is a pattern matching expression which may contain text, hypens and wildcards (e.i. text-text-*). Wildcards match non-empty and non-hypens text.

%common

Revert to unconditional common file part, default at beginning of a file.

%else

Change current conditional state.

%include filename

Include a configuration file, the new file always begin in %common state.

%types type [type ...]

Specify that the current section exhibits the given types. No more than one section can be in use with the same type.

%requiretypes type [type ...]

All specified types must have been defined. May be used in sections or common part.

%set variable content

Set a variable which can be expanded using $(variable) syntax. Environment is initially imported as variables. Moreover $(CONFIGPATH) and $(CONFIGSECTION) are predefined special variables.

%warning text

Produce a warning message

%error text

Produce an error message

The default section name is in use when no section name is passed through the BUILD variable.

Have a look to trunk/mutekh/examples/hello/config for an example of advanced build configuration file.

Developer point of view

MutekH has a component-based architecture where each module declares its configuration tokens.

Tokens are declared is constraint configuration files which located at various places in the MutekH source tree. These constraints configuration files have a different syntax from the build configuration files. They are designed to declare configuration tokens and express relationships between available tokens.

Declared tokens can have their value changed in build configuration files and can be tested from C source code and Makefile.

The .config constraints files

For each configuration token, one may use the following tags:

desc Description string without quotes

Short description about the token

default value

Set the token default value. defined and undefined values act as booleans.

depend TOKEN […]

Dependencies, having at least one of the tokens on the line is required, if unsatisfied the current token gets undefined and a warning is emitted. May be used to disable features because of missing prerequisites.

parent TOKEN

Hierarchical dependency, it ensures all token with a parent gets silently undefined if the parent is undefined. This prevents options enabled by default to stay enabled if the parent is disabled; this way it avoids errors due to unneeded requirements. This is also used to hide unrelevant tokens from the help screen if the parent token is undefined.

require TOKEN […]

Mandatory requirements, having at least one of the tokens on the line is mandatory, conflict yields error. May be usd to enforce definition of some mandatory configuration values.

provide TOKEN […]

Defining the current token enforce definition of the specified token.

provide TOKEN=value

Defining the current token enforce definition of the specified token with the given value.

provide TOKEN=+value

Defining the current token enforce definition of the specified token and concat the given value.

exclude TOKEN

Mandatory excluded tokens, the specified token must not be defined

suggest TOKEN […]

Makes a token suggest other tokens when it is defined. This is for help listing.

single TOKEN […]

Only one of the following tokens may be defined at the same time

fallback TOKEN

The fallback token will be enabled if the current one may not be enabled

The configuration tool may use multiple pass to find a valid configuration when tokens are disabled or enforced by given rules.

Example:

%module Module name for documentation

%config CONFIG_SRL
desc MutekS API
provide CONFIG_MODULES=+libsrl:$(CONFIGPATH)
depend CONFIG_MUTEK_SCHEDULER
depend CONFIG_MWMR
require CONFIG_SRL_SOCLIB CONFIG_SRL_STD
single CONFIG_SRL_SOCLIB CONFIG_SRL_STD
default undefined
%config end

Here we declare a CONFIG_SRL token which

• depends on CONFIG_MUTEK_SCHEDULER and CONFIG_MWMR,
• requires CONFIG_SRL_SOCLIB or CONFIG_SRL_STD,
• adds the directory containing the .config as a new "libsrl" module

Environment variable substitution takes place in both build and constraints configuration files.

The directories Makefile syntax & rules

Makefiles in directories may use the following variables:

objs

A list of .o files compiled from .c, .s or .S files

meta

A list of files that may be translated from .m4, .cpp or .def files

copy

A list of files that must be copied verbatim from source directory to object directory

subdirs

A list of subdirectories where more files are to be processed. These directories must exist and contain a Makefile.

doc_headers

A list of header files which must be parsed to generate the MutekH API reference manual, see header documentation for details.

Makefiles may contain optional flags that may be used for compilation:

file.o_CFLAGS=…

CFLAGS to use for a given object

DIR_CFLAGS=…

CFLAGS to use for all the objects compiled by the current Makefile. Flags added by this setting add-up with the object-specific ones above.

Moreover, one may use ifeq (…,…) make constructs to conditionally compile different things. Configuration tokens are usable.

Example:

objs = main.o

ifeq ($(CONFIG_SRL_SOCLIB),defined)
objs += barrier.o sched_wait.o srl_log.o hw_init.o
else
objs += posix_wait_cycles.o
endif

main.o_CFLAGS = -O0 -ggdb

The arch & cpu specific parts

Architecture and CPU directories have some special files which are injected in the building process:

• config.mk, included by make. It can define some compilation flags
• ldscript, invoked at link-time.
  • Architecture ldscript must create a loadable binary
  • CPU ldscript usually only specifies the entry point name

config.mk

The arch config.mk may override the following variables:

ARCHCFLAGS

C-compiler flags

ARCHLDFLAGS

Linker flags

LD_NO_Q

Linker for the current architecture does not support -q switch, this slightly changes the linking process.

HOSTCPPFLAGS

Flags to give to host's cpp (HOSTCPP) program. This is only used for expansion of .def files.

The cpu config.mk may override the following variables:

CPUCFLAGS

C-compiler flags

CPULDFLAGS

Linker flags

ldscript

Try info ld for a guide through ldscripts…

This ldscript is taken from architecture's object directory, thus it may be obtained from either:

• copy
• m4 processing
• cpp processing

See arch/emu/ldscript, arch/soclib/ldscript.m4, and arch/simple/ldscript.cpp for the three flavors !

Notes

Prerequisites

The MutekH build-system is based on GNU Make features. It makes intensive use of:

• includes
• $(foreach) $(subst) $(eval) $(call) macros
• macro definitions

Therefore, a Make-3.81 at least is mandatory.