Re: [Buildroot] [PATCH v1 2/3] package/log4cxx: fix boost-fallback (only check for boost if really needed)

From: Thomas Petazzoni via buildroot <buildroot@buildroot.org>
To: Peter Seiderer <ps.report@gmx.net>
Cc: Fabrice Fontaine <fontaine.fabrice@gmail.com>, buildroot@buildroot.org
Subject: Re: [Buildroot] [PATCH v1 2/3] package/log4cxx: fix boost-fallback (only check for boost if really needed)
Date: Sun, 30 Jan 2022 23:40:14 +0100	[thread overview]
Message-ID: <20220130234014.3cf1a805@windsurf> (raw)
In-Reply-To: <20220128124538.31789-2-ps.report@gmx.net>

On Fri, 28 Jan 2022 13:45:37 +0100
Peter Seiderer <ps.report@gmx.net> wrote:

> - add patch 0002-boost-fallback-only-check-for-boost-if-really-needed.patch
>   to check for boost if really needed (in case of legacy c++ standard < c++17)
> 
> Fixes:
> 
>   - http://autobuild.buildroot.net/results/8d49ab7cd9952f6a13bdd330e875012d0601f1d2
> 
>   -- Found Boost: .../host/x86_64-buildroot-linux-uclibc/sysroot/usr/include (found version "1.78.0") found components: thread chrono missing components: date_time atomic
>   CMake Error at .../build/log4cxx-0.12.0/boost-fallback-compile-tests/CMakeFiles/CMakeTmp/CMakeLists.txt:19 (add_executable):
>     Target "cmTC_aac37" links to target "Boost::date_time" but the target was
>     not found.  Perhaps a find_package() call is missing for an IMPORTED
>     target, or an ALIAS target is missing?
> 
>   CMake Error at .../build/log4cxx-0.12.0/boost-fallback-compile-tests/CMakeFiles/CMakeTmp/CMakeLists.txt:19 (add_executable):
>     Target "cmTC_aac37" links to target "Boost::atomic" but the target was not
>     found.  Perhaps a find_package() call is missing for an IMPORTED target, or
>     an ALIAS target is missing?
> 
> Signed-off-by: Peter Seiderer <ps.report@gmx.net>
> ---
>  ...nly-check-for-boost-if-really-needed.patch | 36 +++++++++++++++++++
>  1 file changed, 36 insertions(+)
>  create mode 100644 package/log4cxx/0002-boost-fallback-only-check-for-boost-if-really-needed.patch

Took me a while to understand what was going on here, but I think I got it:

 * If we have gcc < 7.x, then log4cxx needs boost, and makes sure boost
   is built with the date-time support.

 * If we have gcc >= 7.x, then log4cxx does not need boost, but the
   CMake logic in src/cmake/boost-fallback/boost-fallback.cmake kicks
   in anyway, and tests if date-time is provided, which fails.

So what your patch does is to only conditionally do the Boost checks in
src/cmake/boost-fallback/boost-fallback.cmake if Boost is really needed.

Looks good to me: applied!

Thanks a lot!

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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