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doc: Description of HOST_TOOLS mechanism

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Norman Feske 2014-05-19 10:11:25 +02:00
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doc/build_system.txt
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@ -325,6 +325,51 @@ variable is present in the 'SPECS' variable as supplied by the build directory
configuration.
Building tools to be executed on the host platform
===================================================
Sometimes, software requires custom tools that are used to generate source
code or other ingredients for the build process, for example IDL compilers.
Such tools won't be executed on top of Genode but on the host platform
during the build process. Hence, they must be compiled with the tool chain
installed on the host, not the Genode tool chain.
The Genode build system accommodates the building of such host tools as a side
effect of building a library or a target. Even though it is possible to add
the tool compilation step to a regular build description file, it is
recommended to introduce a dedicated pseudo library for building such tools.
This way, the rules for building host tools are kept separate from rules that
refer to Genode programs. By convention, the pseudo library should be named
_<package>_host_tools_ and the host tools should be built at
_<build-dir>/tool/<package>/_. With _<package>_, we refer to the name of the
software package the tool belongs to, e.g., qt5 or mupdf. To build a tool
named _<tool>_, the pseudo library contains a custom make rule like the
following:
! $(BUILD_BASE_DIR)/tool/<package>/<tool>:
! $(MSG_BUILD)$(notdir $@)
! $(VERBOSE)mkdir -p $(dir $@)
! $(VERBOSE)...build commands...
To let the build system trigger the rule, add the custom target to the
'HOST_TOOLS' variable:
! HOST_TOOLS += $(BUILD_BASE_DIR)/tool/<package>/<tool>
Once the pseudo library for building the host tools is in place, it can be
referenced by each target or library that relies on the respective tools via
the 'LIBS' declaration. The tool can be invoked by referring to
'$(BUILD_BASE_DIR)/tool/<package>/tool'.
For an example of using custom host tools, please refer to the mupdf package
found within the libports repository. During the build of the mupdf library,
two custom tools fontdump and cmapdump are invoked. The tools are built via
the _lib/mk/mupdf_host_tools.mk_ library description file. The actual mupdf
library (_lib/mk/mupdf.mk_) has the pseudo library 'mupdf_host_tools' listed
in its 'LIBS' declaration and refers to the tools relative to
'$(BUILD_BASE_DIR)'.
Automated integration and testing
#################################