[oe] [RFC] site files for cmake

[Koen Kooi]

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Hi,

After fighting with cmake the weekend (and getting rid of legacy-staging
in console-image while watching cmake fail), I discovered that cmake
supports cross-compiling since 2.6.0 and allows us to provide a site
file using -C. I hacked support for that into cmake.bbclass:

http://cgit.openembedded.org/cgit.cgi/openembedded/commit/?id=ba23d4de95a33db5feccd19359bd9b907c2d90bd

I would like to propose to extend that by copying extending
siteinfo.bbclass with knowledge about cmake site files. It would do
roughy the following:

1) Build a list of appropriate filenames
2) if they exist concatenate them into ${WORKDIR}/site-file.cmake

The sucky part is that you can't use the cmake cache file to populate
the site files like we can with autotools :(

Cmake emits CMakeCache.txt with entries like:

//Result from TRY_RUN
HAVE_POLL_FINE:STRING=0

//Output from TRY_RUN
HAVE_POSIX_STRERROR_R__TRYRUN_OUTPUT:STRING=1

But the site file needs to look like this:

SET( HAVE_POSIX_STRERROR_R
     "1"
     CACHE STRING "Result from TRY_RUN" FORCE)

SET( HAVE_POSIX_STRERROR_R__TRYRUN_OUTPUT
     "1"
     CACHE STRING "Output from TRY_RUN" FORCE)

So to generate missing entries one needs to:

1) Try building app using OE
2) Append TryRunResults.cmake to site-file.cmake
3) Try building app on target
4) Edit the new entries in site-file.cmake using CMakeCache.txt from the
target

if error, goto 1)

5) seperate out new entries into the proper site file (e.g. common,
glibs, arm, etc)

For more info see http://www.itk.org/Wiki/CMake_Cross_Compiling

Oh, and cmake can't crosscompile itself out of the box, it tries to run
generated binaries.

Could cmake gurus comment on all this? Or better, write a tool that
converts a cmakelist.txt to configure.ac, since I know how to fix
autotools :)

regards,

Koen
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