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libbsd.txt: Add guide for user space tools.

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Christian Mauderer 2016-07-06 16:06:54 +02:00
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@ -760,6 +760,36 @@ The report lists the files change based on the opacity level. The opacity is a
measure on how much of a file differs from the original FreeBSD source. The
lower the value the more transparent the source file it.
== Porting of user space utilities
The theory behind the described method is to put all BSS and initialized data
objects into a named section. This section then will be saved before the code is
executed and restored after it has finished. This method limits to a single
threaded execution of the application but minimizes the necessary changes to the
original FreeBSD code.
. Import and commit the unchanged source files like described above.
. Add the files to the libbsd.py and build them.
. Use nm on the generated object files to find out which objects are initialized
(either in BSS -- type b or B -- or in the initialized data segment -- type d
or D). An example call could look like follows:
`arm-rtems4.12-nm build/arm-rtems4.12-xilinx_zynq_a9_qemu/freebsd/contrib/pf/pfctl/pfctl.c.10.o | grep ' [DdbB] '`
. Check the sources for everything that can be made const. This type of patches
should go back to the upstream FreeBSD sources.
. Check the sources for every global variable that can be made static. This type
of patches should go back to the upstream FreeBSD sources.
. Move static variables out of functions. This patches should also go upstream.
. Create one `xxx-data.h` file per c module. This header should contain
declarations for the remaining initialized objects matching the original
declarations but adding a section attribute. The section name has to match the
name of the RTEMS_LINKER_RWSET defined further below. For an example look at
`freebsd/contrib/pf/pfctl/pfctl-data.h`.
. Include the header files at the end of the corresponding c files.
. Add a rtems_bsd_command_xxx wrapper function to the c file containing the main
function. For an example look at `rtems_bsd_command_pfctl(...)` in
`freebsd/contrib/pf/pfctl/pfctl.c`.
. Create one compilable commit.
== Initialization of the BSD Library
The initialization of the BSD library is based on the FreeBSD SYSINIT(9)