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<HTML
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REL="HOME"
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TITLE="The eCos Component Writer's Guide"
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HREF="cdl-guide.html"><LINK
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><TH
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ALIGN="center"
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>The <SPAN
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>eCos</SPAN
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> Component Writer's Guide</TH
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>Prev</A
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CLASS="CHAPTER"
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><H1
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><A
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NAME="BUILD">Chapter 4. The Build Process</H1
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><DIV
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CLASS="TOC"
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><DL
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><DT
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><B
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>Table of Contents</B
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></DT
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><DT
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><A
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HREF="build.html#BUILD.OUTLINE"
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>Build Tree Generation</A
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></DT
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><DT
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><A
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HREF="build.headers.html"
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>Configuration Header File Generation</A
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></DT
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><DT
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><A
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HREF="build.make.html"
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>Building eCos</A
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></DT
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><DT
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><A
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HREF="build.tests.html"
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>Building Test Cases</A
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></DT
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></DL
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></DIV
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><P
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>Some <SPAN
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CLASS="APPLICATION"
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>CDL</SPAN
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> properties describe the consequences of manipulating
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configuration options. There are two main types of consequences.
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Typically enabling a configuration option results in one or more
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<TT
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CLASS="LITERAL"
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>#define's</TT
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> in a configuration header file, and
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properties that affect this include <SPAN
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CLASS="PROPERTY"
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>define</SPAN
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>, <SPAN
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CLASS="PROPERTY"
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>define_proc</SPAN
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> and
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<SPAN
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CLASS="PROPERTY"
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>no_define</SPAN
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>. Enabling a configuration option can also affect the build
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process, primarily determining which files get built and added to the
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appropriate library. Properties related to the build process include
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<SPAN
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CLASS="PROPERTY"
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>compile</SPAN
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> and <SPAN
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CLASS="PROPERTY"
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>make</SPAN
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>. This chapter describes the whole build process,
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including details such as compiler flags and custom build steps.</P
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><P
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>Part of the overall design of the <SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
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> component framework is that
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it can interact with a number of different build systems. The most
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obvious of these is <SPAN
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CLASS="APPLICATION"
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>GNU
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make</SPAN
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>:the component framework can generate one or more
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makefiles, and the user can then build the various packages simply by
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invoking <SPAN
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CLASS="APPLICATION"
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>make</SPAN
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>. However it
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should also be possible to build <SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
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> by other means: the
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component framework can be queried about what is involved in building
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a given configuration, and this information can then be fed into the
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desired build system. Component writers should be aware of this
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possibility. Most packages will not be affected because the <SPAN
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CLASS="PROPERTY"
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>compile</SPAN
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>
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property can be used to provide all the required information, but care
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has to be taken when writing custom build steps.</P
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="BUILD.OUTLINE">Build Tree Generation</H1
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><P
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>It is necessary to create an <SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
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> configuration before anything can
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be built. With some tools such as the graphical configuration tool
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this configuration will be created in memory, and it is not essential
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to produce an <TT
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CLASS="FILENAME"
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>ecos.ecc</TT
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> savefile first (although
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it is still very desirable to generate such a savefile at some point,
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to allow the configuration to be re-loaded later on). With other tools
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the savefile is generated first, for example using
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<TT
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CLASS="LITERAL"
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>ecosconfig new</TT
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>, and then a build tree is
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generated using <TT
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CLASS="LITERAL"
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>ecosconfig tree</TT
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>. The savefile
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contains all the information needed to recreate a configuration.</P
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><P
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>An <SPAN
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CLASS="APPLICATION"
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>eCos</SPAN
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> build actually involves three separate trees. The component
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repository acts as the source tree, and for application developers
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this should be considered a read-only resource. The build tree is
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where all intermediate files, especially object files, are created.
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The install tree is where the main library
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<TT
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CLASS="FILENAME"
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>libtarget.a</TT
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>, the exported header files, and
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similar files end up. Following a successful build it is possible to
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take just the install tree and use it for developing an application:
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none of the files in the component repository or the build tree are
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needed for that. The build tree will be needed again only if the user
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changes the configuration. However the install tree does not contain
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copies of all of the documentation for the various packages, instead
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the documentation is kept only in the component repository.</P
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><P
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>By default the build tree, the install tree, and the
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<TT
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CLASS="FILENAME"
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>ecos.ecc</TT
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> savefile all reside in the same
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directory tree. This is not a requirement, both the install tree and
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the savefile can be anywhere in the file system.</P
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><P
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>It is worth noting that the component framework does not separate the
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usual <TT
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CLASS="LITERAL"
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>make</TT
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> and <TT
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CLASS="LITERAL"
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>make install</TT
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>
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stages. A build always populates the install tree, and any
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<TT
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CLASS="LITERAL"
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>make install</TT
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> step would be redundant.</P
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><P
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>The install tree will always begin with two directories, <TT
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CLASS="FILENAME"
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>include</TT
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> for the exported header files and
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<TT
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CLASS="FILENAME"
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>lib</TT
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> for the main library
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<TT
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CLASS="FILENAME"
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>libtarget.a</TT
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> and other files
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such as the linker script. In addition there will be a subdirectory
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<TT
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CLASS="FILENAME"
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>include/pkgconf</TT
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> containing the
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configuration header files, which are generated or updated at the same
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time the build tree is created or updated. More details of header file
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generation are given below. Additional <TT
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CLASS="FILENAME"
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>include</TT
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> subdirectories such as <TT
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CLASS="FILENAME"
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>sys</TT
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> and <TT
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CLASS="FILENAME"
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>cyg/kernel</TT
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> will be created during the
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first build, when each package's exported header files are copied to
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the install tree. The install tree may also end up with additional
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subdirectories during a build, for example as a result of custom build
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steps. </P
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><P
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>The component framework does not define the structure of the build
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tree, and this may vary between build systems. It can be assumed that
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each package in the configuration will have its own directory in the
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build tree, and that this directory will be used for storing the
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package's object files and as the current directory for any build
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steps for that package. This avoids problems when custom build steps
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from different packages generate intermediate files which happen to
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have the same name.</P
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><P
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>Some build systems may allow application developers to copy a source
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file from the component repository to the build tree and edit the
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copy. This allows users to experiment with small changes, for example
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to add a couple of lines of debugging to a package, without having to
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modify the master copy in the component repository which could be
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shared by several projects or several people. Functionality such as
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this is transparent to component writers, and it is the responsibility
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of the build system to make sure that the right thing happens.</P
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><DIV
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CLASS="NOTE"
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><BLOCKQUOTE
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CLASS="NOTE"
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><P
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><B
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>Note: </B
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>There are some unresolved issues related to the build tree and install
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tree. Specifically, when updating an existing build or install tree,
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what should happen to unexpected files or directories? Suppose the
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user started with a configuration that included the math library, and
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the install tree contains header files <TT
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CLASS="FILENAME"
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>include/math.h</TT
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> and <TT
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CLASS="FILENAME"
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>include/sys/ieeefp.h</TT
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>. The user then removed
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the math library from the configuration and is updating the build
|
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tree. It is now desirable to remove these header files from the
|
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install tree, so that if any application code still attempts to use
|
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the math library this will fail at compile time rather than at link
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time. There will also be some object files in the existing
|
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<TT
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CLASS="LITERAL"
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|
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>libtarget.a</TT
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> library which are no longer
|
| 325 |
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appropriate, and there may be other files in the install tree as a
|
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result of custom build steps. The build tree will still contain a
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directory for the math library, which no longer serves any purpose.</P
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|
|
><P
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>However, it is also possible that some of the files in the build tree
|
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or the install tree were placed there by the user, in which case
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|
removing them automatically would be a bad idea.</P
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|
|
><P
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>At present the component framework does not keep track of exactly what
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should be present in the build and install trees, so it cannot readily
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determine which files or library members are obsolete and can safely
|
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be removed, and which ones are unexpected and need to be reported to
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the user. This will be addressed in a future release of the system.</P
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></BLOCKQUOTE
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></DIV
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></DIV
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></DIV
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><DIV
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="language.database.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="cdl-guide.html"
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ACCESSKEY="H"
|
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>Home</A
|
| 370 |
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></TD
|
| 371 |
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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><A
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HREF="build.headers.html"
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ACCESSKEY="N"
|
| 378 |
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>Next</A
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| 379 |
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></TD
|
| 380 |
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></TR
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><TR
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><TD
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WIDTH="33%"
|
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ALIGN="left"
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| 385 |
|
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VALIGN="top"
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|
|
>Updating the <SPAN
|
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CLASS="DATABASE"
|
| 388 |
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>ecos.db</SPAN
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| 389 |
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> database</TD
|
| 390 |
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><TD
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| 391 |
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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> </TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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| 398 |
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VALIGN="top"
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>Configuration Header File Generation</TD
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| 400 |
|
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></TR
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| 401 |
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></TABLE
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| 402 |
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></DIV
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></BODY
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></HTML
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>
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