问题
I have LLVM 3.3 with Clang, and
$ /tmp/clang/bin/clang -print-search-dirs
programs: =/tmp/clang/bin:/usr/lib/gcc/i486-linux-gnu/4.4/../../../../i486-linux-gnu/bin
libraries: =/tmp/clang/bin/../lib/clang/3.3:/usr/lib/gcc/i486-linux-gnu/4.4:/usr/lib/gcc/i486-linux-gnu/4.4/../../../../lib32:/usr/lib/../lib32:/usr/lib/i486-linux-gnu/../../lib32:/usr/lib/gcc/i486-linux-gnu/4.4/../../..:/lib:/usr/lib
How can I instruct Clang to usage an stdlib (e.g. libgcc) directory other than /usr/lib/gcc/i486-linux-gnu/4.4? I'd like to make it use /tmp/mygccstd instead.
It's also looking in /usr/lib and /lib. How do I disable that?
回答1:
On my system I have 3 compilers installed. gcc-7.3.0, gcc-7.2.0, and clang-6.0
gcc-7.3.0 is installed to the system path and is the system default compiler.
gcc-7.2.0 is installed to /usr/local and is a build requirement for a specific tool.
clang-6.0 is installed to /usr/local and is used for it's stricter warnings/errors.
My boost libraries are compiled with gcc-7.2.0 and I wished to use clang to compile my specific tool. By default, with -stdlib=libstdc++ clang would find gcc-7.3.0 and boost would fail to link.
To get around this I used the following compile flags:
-stdlib=libstdc++ # Tell clang to parse the headers as libstdc++ not libc++
-cxx-isystem /usr/local/include/c++/7.2.0/ # includes for libstdc++
-cxx-isystem /usr/local/include/c++/7.2.0/x86_64-pc-linux-gnu/ # includes for libstdc
And the following linker flags:
-L/usr/local/lib64/ # static libstdc++
-L/usr/local/lib/gcc/x86_64-pc-linux-gnu/7.2.0/ #static libgcc
You can fill in your own linker paths with the directories that hold libstdc++.a and libgcc.a and these will depend on where your compiler is installed to.
回答2:
This is documented in the libcxx docs:
- https://libcxx.llvm.org/docs/UsingLibcxx.html
clang++ -std=c++17 -stdlib=libc++ -nostdinc++ \
-I<libcxx-install-prefix>/include/c++/v1 \
-L<libcxx-install-prefix>/lib \
-Wl,-rpath,<libcxx-install-prefix>/lib \
test.cpp
<libcxx-install-prefix> will be the <location of clang binary>/../../
This stops the compiler from using system dylib.
- How to specify custom libc++
- When running clang built from source, how to specify location of libc++, or, someone explain to me what -stdlib=libc++ does
回答3:
A combination of -B and --sysroot did the trick for the libraries. A combination of -nostdinc, -isystem and -cxx-isystem did the trick for the includes. Not all these flags are displayed by clang --help, some of them I learned from man gcc, some other reading the Clang source code, and some other online.
-gcc-toolchain also made a difference, but it was using weird rules to find the libraries, disallowing symlinks in the pathname components etc., so I ended up using the other flags above instead.
来源：https://stackoverflow.com/questions/20530105/how-to-specify-a-custom-stdlib-directory-for-llvm