Building Existing Software Packages with EMAC OE SDK

Table 1: Conventions
/download/directory/	The directory to which the SDK archive will be downloaded.
/path/to/sdk/	The directory to which the SDK will be extracted.
EMAC-OE-arm-linux-gnueabi-SDK_XX.YY.rZZ.tar.bz2 EMAC-OE-arm-linux-gnueabi-SDK_XX.YY	XX - the SDK major version YY - the SDK minor version ZZ - the SDK current revision
target_program	The program executable created to run on the target device.
developer@ldc:~$	Prompt and commands to be run on a development machine that will run compliation tasks.
root@emac-oe:~#	Prompt and commands to be run on a target machine.

It is very common to need to be able to build existing software projects for the target hardware rather than developing the software from scratch. This feature is especially important in an open source environment, where countless libraries and utilities are available for use and often times need to be compiled to match the target architecture. Fortunately, EMAC OE SDK toolchains are standard GCC packages designed and configured to make this process as easy as possible. In addition, most software projects are developed to allow for cross-platform development.

This guide provides an overview of the most common tasks associated with compiling existing software projects using the SDK. Note, however, that build methods differ significantly depending on the project design. Refer to the project documentation or support for information on how to cross-compile the software; the EMAC OE SDK can be treated as a standard GCC toolchain in this respect. Table 1 below denotes some conventions used in this guide.

Makefile-based Projects

Some projects have a build system based on a set of makefiles that are responsible for compiling and packaging the software. In general, configuring these projects to compile using the EMAC OE SDK is a simple process. In some instances, the software designers may have included a variable in the makefile which allows a cross-compiler prefix setting. In other cases, the CC and other makefile variables can be modified to direct make to compile using the EMAC OE SDK.

It may be advantageous to add the cross-compiler bin directory to the system PATH variable temporarily before compiling to simplify Makefile modifications. This can be done with a command such as the following:

developer@ldc:~$ export PATH=$PATH:/path/to/sdk/EMAC-OE-arm-linux-gnueabi-SDK_XX.YY/gcc-4.2.4-arm-linux-gnueabi/bin

MTD Utilities Project Example

The MTD Utilities project mtd-utils is a good example of a Makefile-based build system that can easily be built using the EMAC OE SDK. Follow the steps below to accomplish this task.

1. Begin by downloading the mtd-utils source code. Assuming that git is installed on the development system, run the following command to get the most recent version. Note that this version will be different from the stable release installed on EMAC OE systems by default.

developer@ldc:~$ git clone git://git.infradead.org/mtd-utils.git

1. After downloading the source, navigate to the source directory mtd-utils and open Makefile in the top-level directory. This file defines various make targets and compilation flags used to compile the source. Notice that the file common.mk is sourced with the line include common.mk. This is similar to the global.properties file in the EMAC OE SDK.
2. Close the Makefile editor and open the common.mk file. At the top of the file, CC, AR, and RANLIB are defined using the CROSS variable, which is not set in either common.mk or Makefile. An exert is shown below:

CC := $(CROSS)gcc
AR := $(CROSS)ar
RANLIB := $(CROSS)ranlib

If the CROSS variable is defined when make is run, the specific toolchain to use can be specified. Also note that CFLAGS is defined using a ?= assignment, which means that the assignment will only be made if CFLAGS is undefined:

CFLAGS ?= -O2 -g

1. Close common.mk without making any changes.
2. In order to compile the source correctly, the CROSS and CFLAGS variables should be defined. The tuning flags for the target architecture to be added to the CFLAGS variable should be used from the ARCHFLAGS variable in the global.properties file of the EMAC OE SDK. The following steps utilize tuning flags for an armv5te processor-based system. Although the path to the SDK toolchain could be included directly in the CROSS variable in this instance, this example works by adding the SDK toolchain to the system PATH variable. The path and prefix used will differ depending on the target architecture of the EMAC OE SDK; refer to global.properties in the SDK to determine the correct settings. The DESTDIR variable controls where the files are put when running the install make target. The WITHOUT_XATTR flag must be set to disable features of the software that are not available on EMAC OE.
   1. Before compiling, several source changes are required to match the setup of the SDK. These include changing references from lzo2 to lzo, and changing the lzo include prefix. Run the following commands from the mtd-utils directory to make these changes:

developer@ldc:~$ for file in `find . -name Makefile`; do sed -i 's:lzo2:lzo:g' $file; done
developer@ldc:~$ for file in `find . -name '*.c'`; do sed -i 's:lzo/::g' $file; done

1. 1. Run the following commands to set the variables:

developer@ldc:~$ export PATH=$PATH:/path/to/sdk/EMAC-OE-arm-linux-gnueabi-SDK_XX.YY/gcc-4.2.4-arm-linux-gnueabi/bin
developer@ldc:~$ export CROSS=arm-linux-gnueabi-
developer@ldc:~$ export CFLAGS="-O2 -g -march=armv5te -mtune=arm926ej-s"
developer@ldc:~$ export DESTDIR=Install
developer@ldc:~$ export WITHOUT_XATTR=1

1. Once the environment has been set up, make can be used to compile the source code:

developer@ldc:~$ make all

1. After successfully compiling the project, the install make target can be used to package all of the software into the Install directory as specified by the DESTDIR variable:

developer@ldc:~$ make install
developer@ldc:~$ ls -R Install

Install:
usr
 
Install/usr:
sbin  share
 
Install/usr/sbin:
docfdisk      flash_erase     flash_lock      flash_unlock  jffs2dump   nanddump   nftldump     rfddump      sumtool
doc_loadbios  flash_eraseall  flash_otp_dump  ftl_check     mkfs.jffs2  nandtest   nftl_format  rfdformat
flashcp       flash_info      flash_otp_info  ftl_format    mtd_debug   nandwrite  recv_image   serve_image
 
Install/usr/share:
man
 
Install/usr/share/man:
man1
 
Install/usr/share/man/man1:
mkfs.jffs2.1.gz

While the procedure in this example is specific to mtd-utils, many makefile-based projects will require similar steps for cross-compiling.

Autotools-based Projects

The GNU build system is known as Autotools. Autotools is a group of applications that are designed to provide a configurable build system to allow compilation on different platforms and environments. A configure script and set of input files are used to generate makefiles based on options passed to the configure script and deduced from the system environment. This includes tests for compiler options, library functions, install configuration, and other assorted variables.

The configure script is the most important step in building an autotools-based project. Although available options for configure vary depending on the project design, there are common options shared between most autotools projects.

libConfuse Example Project

The libConfuse project is a simple C library written for parsing configuration files. It uses an autotools build system for configuration. The steps below demonstrate how to build libConfuse and should be used as an example for building other autotools-based projects.

1. The source code for the libConfuse project can be downloaded as described on the project website [1]. For this example, release 2.7 is used: [2]. After downloading the source, extract the archive and navigate to the top-level directory of the project (i.e. `confuse-2.7`).
2. Read through the README and INSTALL files for information on the project and general information on how to build it. Also, look at the help output from configure to see a summary of the available options:

developer@ldc:~$ ./configure --help

1. Before beginning, the system PATH variable should be changed to include the SDK toolchain as in the makefile-based project example. The CFLAGS variable should also be set. If the CC variable is set, it should be set to arm-linux-gnueabi-gcc (or the appropriate value for the target); if not set the compiler name will be detected from the options passed to configure. The CFLAGS architecture tuning values should be set according to the global.properties file in the EMAC OE SDK. The DESTDIR variable determines where the files will be installed to when the install make target is run. DESTDIR must be an absolute path for the libConfuse project, so the current working directory is added to the variable using the pwd command. The following commands are an example of how to set up the environment correctly:

developer@ldc:~$ export CFLAGS="-O2 -march=armv5te -mtune=arm926ej-s"
developer@ldc:~$ export DESTDIR=`pwd`/Install

1. After setting the environment, configure can be run with the appropriate options to configure the build system and generate the makefiles. The code below shows an example configuration used by EMAC OE. Be sure to set the host and target correctly based on the architecture:

developer@ldc:~$ ./configure --build=i686-linux --host=arm-linux-gnueabi --target=arm-linux-gnueabi \
        --prefix=/usr --exec_prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin \
        --datadir=/usr/share  \
        --infodir=/usr/share/info \
        --mandir=/usr/share/man --enable-shared

The configuration should complete successfully. If any problems are reported that result in an error, check the environment settings and configure options again.

1. Now that configure has generated all of the makefiles for the project, make can be used to compile the source code:

developer@ldc:~$ make all

If any errors are encountered during compilation, examine the output of configure and make sure that all of the environment variables and configure options were specified correctly.

1. Once compilation is complete, the install target can be used to package all of the necessary files together so that they can be transferred to the target board.

developer@ldc:~$ make install
developer@ldc:~$ ls -R Install

Install:
usr
 
Install/usr:
include  lib  share
 
Install/usr/include:
confuse.h
 
Install/usr/lib:
libconfuse.a  libconfuse.la  libconfuse.so  libconfuse.so.0  libconfuse.so.0.0.0  pkgconfig
 
Install/usr/lib/pkgconfig:
libconfuse.pc
 
Install/usr/share:
locale
 
Install/usr/share/locale:
fr  sv
 
Install/usr/share/locale/fr:
LC_MESSAGES
 
Install/usr/share/locale/fr/LC_MESSAGES:
confuse.mo
 
Install/usr/share/locale/sv:
LC_MESSAGES
 
Install/usr/share/locale/sv/LC_MESSAGES:
confuse.mo

Note that not all of the files installed would be necessary to install on the board, such as the man pages and pkgconfig information.