Hi, Jonathan Wakely <jwakely.gcc@xxxxxxxxx> skribis: > On Wed, 22 Jul 2020 at 21:39, Ludovic Courtès <ludovic.courtes@xxxxxxxx> wrote: >> >> Hello, >> >> While building GCC on a non-FHS distro, we do something like¹: >> >> export CPLUS_INCLUDE_PATH=/path/to/host/gcc/include/c++:/path/to/host/gcc/include > > That looks wrong. Why are you doing this? Doesn't your host GCC > already know where its headers are? It does. With Guix, CPLUS_INCLUDE_PATH is automatically populated with all the include/ and include/c++/ directories of dependencies, which includes GCC’s own libstdc++. We could override that, but I’m trying to understand what’s going on. >> This ensures the host GCC’s C++ headers are found by ‘xgcc’ during >> build. > > Why do you want that to happen? > > It's wrong in general, but it's specifically wrong in your case > because the host compiler is a different version to the one you're > trying to build. There is absolutely no guarantee that GCC 10.1 can > compile the libstdc++ headers from GCC 7.5, and trying to do so is not > supported. Is it wrong? I’m talking about the first time where ‘libstdc++-v3/configure’ runs, which itself checks for C++ features. It’s checking for C++ features of the host compiler/C++ library, isn’t it? Thanks for your feedback! Ludo’.
