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ref-manual: Added two new FAQ entries.

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One has to do with the weird names the build system creates based
on DESTDIR and other variables.

The other has to do with -native recipes not buiding correctly.

(From yocto-docs rev: 32a444a258e3c7c87fdc015475f54e5b34628246)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
2014-08-01 12:06:37 +03:00
committed by Richard Purdie
parent 152d307767
commit e7dae57a98
1 changed files with 106 additions and 0 deletions
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106
documentation/ref-manual/faq.xml
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@@ -682,6 +682,112 @@
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
Why do <filename>${bindir}</filename> and <filename>${libdir}</filename> have strange values for <filename>-native</filename> recipes?
</para>
</question>
<answer>
<para>
Executables and libraries might need to be used from a
directory other than the directory into which they were
initially installed.
Complicating this situation is the fact that sometimes these
executables and libraries are compiled with the expectation
of being run from that initial installation target directory.
If this is the case, moving them causes problems.
</para>
<para>
This scenario is a fundamental problem for package maintainers
of mainstream Linux distributions as well as for the
OpenEmbedded build system.
As such, a well-established solution exists.
Makefiles, Autotools configuration scripts, and other build
systems are expected to respect environment variables such as
<filename>bindir</filename>, <filename>libdir</filename>,
and <filename>sysconfdir</filename> that indicate where
executables, libraries, and data reside when a program is
actually run.
And, they are also expected to respect a
<filename>DESTDIR</filename> environment variable, which is
prepended to all the other variables when the build system
actually installs the files.
It is understood that the program does not actually run from
within <filename>DESTDIR</filename>.
</para>
<para>
When the OpenEmbedded build system uses a recipe to build a
target-architecture program (i.e. one that is intended for
inclusion on the image being built), that program eventually
runs from the root file system of that image.
Thus, the build system provides a value of "/usr/bin" for
<filename>bindir</filename>, a value of "/usr/lib" for
<filename>libdir</filename>, and so forth.
</para>
<para>
Meanwhile, <filename>DESTDIR</filename> is a path within the
<ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>.
However, when the recipe builds a native program (i.e. one
that is intended to run on the build machine), that program
is never installed directly to the build machine's root
file system.
Consequently, the build system uses paths within the Build
Directory for <filename>DESTDIR</filename>,
<filename>bindir</filename> and related variables.
To better understand this, consider the following two paths
where the first is relatively normal and the second is not:
<note>
Due to these lengthy examples, the paths are artificially
broke across lines for readability.
</note>
<literallayout class='monospaced'>
/home/maxtothemax/poky-bootchart2/build/tmp/work/i586-poky-linux/zlib/
1.2.8-r0/sysroot-destdir/usr/bin
/home/maxtothemax/poky-bootchart2/build/tmp/work/x86_64-linux/
zlib-native/1.2.8-r0/sysroot-destdir/home/maxtothemax/poky-bootchart2/
build/tmp/sysroots/x86_64-linux/usr/bin
</literallayout>
The standard <filename>DESTDIR</filename> mechanism leaves no
other choice.
</para>
</answer>
</qandaentry>
<qandaentry>
<question>
<para>
The files provided by my <filename>-native</filename> recipe do
not appear to be available to other recipes.
Files are missing from the native sysroot, my recipe is
installing to the wrong place, or I am getting permissions
errors during the do_install task in my recipe! What is wrong?
</para>
</question>
<answer>
<para>
This situation results when the OpenEmbedded build system does
not recognize the environment variables supplied to it by
<ulink url='&YOCTO_DOCS_DEV_URL;#bitbake-term'>BitBake</ulink>.
The incident that prompted this FAQ entry involved a Makefile
that used an environment variable named
<filename>BINDIR</filename> instead of the more standard
variable <filename>bindir</filename>.
The makefile's hardcoded default value of "/usr/bin" worked
most of the time, but not for the recipe's
<filename>-native</filename> variant.
Consequently, permissions errors might be caused by a Makefile
that ignores <filename>DESTDIR</filename> or uses a different
name for that environment variable.
Check the OpenEmbedded build system to see if these kinds of
issues exist.
</para>
</answer>
</qandaentry>
</qandaset>
</chapter>