[Buildroot] [PATCH 3/4] Makefile: generate CMake toolchain file in $(O)

[Bjørn Forsman]

Hi,

Sorry for the late reply.

2011/1/11 Thomas Petazzoni <thomas.petazzoni at free-electrons.com>:
> Hello,
>
> On Mon, 10 Jan 2011 19:30:16 +0100
> Bjørn Forsman <bjorn.forsman at gmail.com> wrote:
>
>> Yes, I'll add that, thanks! I guess it only matters for the target
>> build and not native build (we don't strip HOST_DIR do we?), but I
>> think I'll add it to native build anyway, for consistency.
>
> I had another two problems with the CMake toolchain file. The first is
> that the CMAKE_C_FLAGS and CMAKE_CXX_FLAGS variables were not taken
> into account. It's more or less explained at
> http://www.mail-archive.com/cmake@cmake.org/msg33248.html why this
> happens. The second problem is that --sysroot was missing at link time,
> so I had to add CMAKE_EXE_LINKER_FLAGS as well.
>
> So I have the following changes:
>
> diff --git a/Makefile b/Makefile
> index 994dd52..b154007 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -378,8 +378,9 @@ $(O)/toolchainfile.cmake:
>        set(CMAKE_PROGRAM_PATH $(HOST_DIR)/usr/bin)\n\
>        set(CMAKE_C_COMPILER $(CMAKE_TARGET_CC))\n\
>        set(CMAKE_CXX_COMPILER $(CMAKE_TARGET_CXX))\n\
> -       set(CMAKE_C_FLAGS \"$(CMAKE_TARGET_CFLAGS)\")\n\
> -       set(CMAKE_CXX_FLAGS \"$(CMAKE_TARGET_CXXFLAGS)\")\n\
> +       set(CMAKE_C_FLAGS \"$(CMAKE_TARGET_CFLAGS)\" CACHE STRING \"\" FORCE)\n\
> +       set(CMAKE_CXX_FLAGS \"$(CMAKE_TARGET_CXXFLAGS)\" CACHE STRING \"\" FORCE)\n\
> +       set(CMAKE_EXE_LINKER_FLAGS \"$(CMAKE_TARGET_LDFLAGS)\" CACHE STRING \"\" FORCE)\n\
>        set(CMAKE_FIND_ROOT_PATH $(STAGING_DIR))\n\
>        set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)\n\
>        set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)\n\
> diff --git a/package/Makefile.cmake.in b/package/Makefile.cmake.in
> index 08a0395..ce50b10 100644
> --- a/package/Makefile.cmake.in
> +++ b/package/Makefile.cmake.in
> @@ -41,6 +41,7 @@ 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)
> +CMAKE_TARGET_LDFLAGS = $(filter --sysroot=%,$(TARGET_LD)) $(TARGET_LDFLAGS)

The FORCE stuff seems like a good idea, thanks!

Hm... I've been thinking about --sysroot, -I and -L flags in the
toolchain-file lately. AFAIK, any CMake package should be able to
build perfectly without manually specifying these flags. Actually, I
would go so far as saying that passing -I, -L (or --sysroot) may hide
bugs in CMakeLists.txt files because a package should use FIND_XXX()
macros and not depend on -I, -L or --sysroot.

However, my impression is that not all CMake packages are looking for
headers and libs using FIND_XXX() and actually relies on -I, -L flags
(or built-in compiler config) to build. Thus, it may be easier to add
these flags to the CMake infrastructure than to fix the packages. But I
think it is a bit of a hack/workaround...

CMAKE_C_FLAGS is a bit special because it includes not only (unneeded)
-I flags, but some important flags such as the -march flag. So we at
least need some way to get -march into the compiler line and using the whole
TARGET_CFLAGS is an easy way to do that. CMAKE_EXE_LINKER_FLAGS
is just -L flags, so this is IMO just a workaround broken packages...

There is also the possibility to pass CMAKE_EXE_LINKER_FLAGS as
<PKG>_CONF_OPT in each broken package.

What do you think?

Best regards,
Bjørn Forsman