[Buildroot] [PATCH 1/4] Add CMAKETARGETS infrastructure for CMake packages

[Bjørn Forsman]

Hi Samuel,

2010/12/13 Samuel Martin <s.martin49 at gmail.com>:
> Hi Bjørn,
> Thanks for submitting these patches that join some of my works, especially
> about generating a cmake-toolchain file. You beat me to the punch ;)
> Details:
>>
>> +# CMake doesn't support having the --sysroot option directly in the
>>
>> +# compiler path, so move this option to the CFLAGS/CXXFLAGS variables.
>>
>> +CMAKE_TARGET_CC = $(filter-out --sysroot=%,$(TARGET_CC))
>>
>> +CMAKE_TARGET_CXX = $(filter-out --sysroot=%,$(TARGET_CXX))
>>
>> +CMAKE_TARGET_CFLAGS = $(filter --sysroot=%,$(TARGET_CC)) $(TARGET_CFLAGS)
>>
>> +CMAKE_TARGET_CXXFLAGS = $(filter --sysroot=%,$(TARGET_CXX))
>> $(TARGET_CXXFLAGS)
>
> I think it is not necessary to add the --sysroot option to any of these
> flags if we correctly define the CMake toolchain file (cf. patch review
> of [PATCH 3/4])

I guess you're right.

>> +# Configure package for target
>>
>> +define $(2)_CONFIGURE_CMDS
>>
>> +       (cd $$($$(PKG)_SRCDIR) && \
>
> You configure and build in the source tree, why not.. but CMake
> supports (i'd like to say: it's designed to) build out of source tree (and
> it messes up a bite the build tree...).

I agree, it's a bit messy. But where to but the build tree? Inside the
srctree or in a directory at the same level? I guess I would prefer the
latter, something like

srctree:
  output/build/cdrkit-1.1.10

buildtree:
  output/build/cdrkit-1.1.10.build

But as the autotools infrastructure does (AFAIK) buildtree == srctree, I
just did the same.

>>
>> +       rm -f CMakeCache.txt && \
>>
>> +       $$($$(PKG)_CONF_ENV) $(HOST_DIR)/usr/bin/cmake $$($$(PKG)_SRCDIR)
>> \
>>
>> +               -Wno-dev \
>>
>> +               -DCMAKE_SYSTEM_NAME:STRING="Linux" \
>>
>> +               -DCMAKE_C_COMPILER:FILEPATH="$$(CMAKE_TARGET_CC)" \
>>
>> +               -DCMAKE_CXX_COMPILER:FILEPATH="$$(CMAKE_TARGET_CXX)" \
>>
>> +               -DCMAKE_C_FLAGS:STRING="$$(CMAKE_TARGET_CFLAGS)" \
>>
>> +               -DCMAKE_CXX_FLAGS:STRING="$$(CMAKE_TARGET_CXXFLAGS)" \
>>
>> +               -DCMAKE_EXE_LINKER_FLAGS:STRING="$$(TARGET_LDFLAGS)" \
>>
>> +               -DCMAKE_MODULE_LINKER_FLAGS:STRING="$$(TARGET_LDFLAGS)" \
>>
>> +               -DCMAKE_SHARED_LINKER_FLAGS:STRING="$$(TARGET_LDFLAGS)" \
>>
>> +               -DCMAKE_FIND_ROOT_PATH:PATH="$$(STAGING_DIR)" \
>>
>> +               -DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM:STRING="NEVER" \
>>
>> +               -DCMAKE_FIND_ROOT_PATH_MODE_LIBRARY:STRING="ONLY" \
>>
>> +               -DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE:STRING="ONLY" \
>
> Why don't you use the -DCMAKE_TOOLCHAIN_FILE <cmake-toolchain-file> here
> instead of all these -D... ?

Good question :-)

1) It's because the toolchain-file patch was written after this :-)

2) The -D... flags come from cdrkit.mk, which I used as "template" for
CMAKETARGETS. Some of the flags I'm not sure if are right (or is needed)
for a toolchain-file:

CMAKE_{C,CXX}_FLAGS, CMAKE_{EXE,MODULE,SHARED}_LINKER_FLAGS

Neither of these are listed in CMake Cross-compiling page[1].

So, I took the easy way out: build CMake packages inside Buildroot using
cdrkit.mk settings (should cause minimal breakage) and add a minimal
toolchain-file for out-of-Buildroot packages which just have the bare
minimum of settings.

I will take another look at the above CMake variables during a build, and
try to come up with a minimal toolchain-file that can work well internally
and externally.

However, isn't there a little conflict between internal and external use?
For internal use I'd like Buildroot to force build configurations on all
packages, like Debug/Release. but for external packages I'd like to control
this in the package itself. Maybe we should use the same toolchain-file
internally and externally, but give CMake CFLAGS/CXXFLAGS on the
commandline when building internal packages?

[1] the http://www.vtk.org/Wiki/CMake_Cross_Compiling

Best regards,
Bjørn Forsman