Missing C++ headers when cross compiling from Darwin-ARM64 to Linux-x86-64 with Debian sysroot

[mutalibmohammed]

I'm trying to cross-compile from MacOS arm64 to Linux x86-64 while using libstdc++ instead of libc++. I've created a sysroot based on Debian Trixie with libstdc++. The C++ headers are located in: /usr/include/c++/14 The sysroot was created with sudo debootstrap --arch=amd64 --variant=minbase stable sysroot-deb-amd64-stable.

When I compile my project, clang is unable to find the C++ headers.

This is the search path it uses.

#include <...> search starts here:
external/toolchains_llvm++llvm+llvm_toolchain_llvm/lib/clang/20/include
external/+_repo_rules+org_chromium_sysroot_linux_amd64/usr/include/x86_64-linux-gnu
external/+_repo_rules+org_chromium_sysroot_linux_amd64/usr/include
End of search list.

However, when I use the Debian Stretch sysroot that is used in toolchains_llvm tests, I observe these search paths:

#include <...> search starts here:
 external/+_repo_rules2+org_chromium_sysroot_linux_amd64/usr/lib/gcc/x86_64-linux-gnu/6/../../../../include/c++/6
 external/+_repo_rules2+org_chromium_sysroot_linux_amd64/usr/lib/gcc/x86_64-linux-gnu/6/../../../../include/x86_64-linux-gnu/c++/6
 external/+_repo_rules2+org_chromium_sysroot_linux_amd64/usr/lib/gcc/x86_64-linux-gnu/6/../../../../include/c++/6/backward
 external/toolchains_llvm++llvm+llvm_toolchain_llvm/lib/clang/20/include
 external/+_repo_rules2+org_chromium_sysroot_linux_amd64/usr/include/x86_64-linux-gnu
 external/+_repo_rules2+org_chromium_sysroot_linux_amd64/usr/include
End of search list.

What am I missing from my sysroot that is causing Clang to not find the installed headers? What workaround can I use in Bazel to correctly configure the llvm toolchain?

clang version 20.1.2 (https://github.com/llvm/llvm-project 58df0ef89dd64126512e4ee27b4ac3fd8ddf6247)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: external/toolchains_llvm++llvm+llvm_toolchain_llvm/bin
Found candidate GCC installation: external/+_repo_rules+org_chromium_sysroot_linux_amd64/lib/gcc/x86_64-linux-gnu/14
Selected GCC installation: external/+_repo_rules+org_chromium_sysroot_linux_amd64/lib/gcc/x86_64-linux-gnu/14
Candidate multilib: .;@m64
Selected multilib: .;@m64

[scasagrande]

You can build your own:

• https://steven.casagrande.io/posts/2024/sysroot-generation-toolchains-llvm/
• https://github.com/scasagrande/toolchains_llvm_sysroot

Use rules_distroless and Debian bookworm as a base:

• https://github.com/malt3/sysroots

And I remember seeing another example where a sysroot was built by layering the exact desired deb files, but I don't have the link handy right now