Hi, we also had this problem and the thing it that clang checks for a valid GCC/libstdc++ installation by looking for the crtbegin.o file in the related lib directory. So it doesn't work if you just have the headers for libstdc++, you also need to recreate the folder-structure that leads to the crtbegin.o file, otherwise clang doesn't recognize this as a valid sysroot.
There are some patches on the phabricator to fix this, but I don't think any of them has landed yet. Otherwise look in the /test/ directory and grep for "--sysroot" to get a more examples. Cheers, - Raphael 2017-06-13 14:55 GMT+02:00 Paul Smith via cfe-users <cfe-users@lists.llvm.org>: > Can someone point to any detailed information about how these flags > work? I have a custom-compiled version of GCC on Linux and I'm trying > to build Clang 4.0.0 for this system as well. I would like it to use > libstdc++ from my custom-compiled GCC installation to allow linking of > other libraries built with libstdc++. > > I also have a sysroot that I use with GCC so it compiles against a known > set of system headers and libraries (based on Red Hat 6.3 in this case). > This sysroot is directly extracted from a Red Hat system (technically, > it's extracted from the RPMs) so the layout is straightforward and using > the --sysroot for GCC locates it without any problems. > > However, I can't get clang to work with either of these environments no > matter what options I provide it. > > For --sysroot for example, I have this: > > /my/sysroot/lib > /my/sysroot/lib64 > /my/sysroot/usr/include > /my/sysroot/usr/lib > /my/sysroot/usr/lib64 > /my/sysroot/usr/libexec > > If I use "gcc --sysroot=/my/sysroot" all works fine. If I use "clang > --syroot=mysysroot" no system headers are found. I used strace on the > clang binary to try to figure out what it's looking for and it searches > for all of these things in my sysroot directory: > > /my/sysroot/usr/local/cuda > /my/sysroot/usr/local/cuda-8.0 > /my/sysroot/usr/local/cuda-7.5 > /my/sysroot/usr/local/cuda-7.0 > /my/sysroot/lib/x86_64-linux-gnu > /my/sysroot/lib/x86_64-generic-linux-gnu >> /my/sysroot/lib/../lib64 > /my/sysroot/usr/lib/x86_64-generic-linux-gnu >> /my/sysroot/usr/lib/../lib64 > /my/sysroot/usr/lib/x86_64-generic-linux-gnu/../../lib64 >> /my/sysroot/lib >> /my/sysroot/usr/lib > > Of these only the four marked exist in my sysroot. But the big thing > here is that at no time does clang look for /my/sysroot/usr/include, and > indeed when the preprocessor tries to find headers it doesn't look > there, and none of my system header files are found! > > Do I have to add these myself with -isystem even when I specify > --sysroot and the header directory is right there? Is --sysroot not > intended to be used to locate header files? > > > For --gcc-toolchain the situation is similar although clang looks in > MANY more places to try to locate the GCC toolchain. However, I build > GCC myself and I have a completely standard installation: what you get > when you run make / make install after a configure --prefix. My GCC > installation looks like: > > /my/gcc/bin > /my/gcc/lib/gcc/x86_64-generic-linux-gnu/7.1.0/include > /my/gcc/lib64 > /my/gcc/libexec/gcc/x86_64-generic-linux-gnu/7.1.0 > /my/gcc/x86_64-generic-linux-gnu/bin > /my/gcc/x86_64-generic-linux-gnu/include/c++/7.1.0/... > > /my/gcc/x86_64-generic-linux-gnu/include/c++/7.1.0/x86_64-generic-linux-gnu/... > /my/gcc/x86_64-generic-linux-gnu/lib > /my/gcc/x86_64-generic-linux-gnu/lib64 > > (I have a GCC 6.2 install too and the layout is basically identical.) > When I use --gcc-toolchain with clang it looks in about 50 different > directories but doesn't seem to be able to locate this: a standard > unmodified installation of GCC. I've tried numerous different values > for --gcc-toolchain but none seem to work. > > > Am I doing something wrong here? Or is this just not going to work and > I'll have to figure out all the include directories, etc. I need by hand > and add them via -isystem etc. myself? > > > Thanks for any help you can provide! > _______________________________________________ > cfe-users mailing list > cfe-users@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users _______________________________________________ cfe-users mailing list cfe-users@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
