https://github.com/rossburton created https://github.com/llvm/llvm-project/pull/160605
When cross-compiling the LLVM project as a whole (from llvm/), if it cannot find presupplied tools it will create a native build environment to build the tools it needs. However, when doing a standalone build of clang (that is, from clang/ and linking against an existing libLLVM) this doesn't work. Instead a _target_ binary is built which predictably then fails. The conventional workaround for this is to build the native tools in a separate native compile phase and pass the paths to the cross build, for example see OpenEmbedded[1] or Nix[2]. But we can do better! The first problem is that LLVM_USE_HOST_TOOLS is only set in the llvm/ CMakeLists.txt, so setup_host_tool() will never consider building a native binary. This can be solved by setting LLVM_USE_HOST_TOOLS based on CMAKE_CROSSCOMPILING in clang/CMakeLists.txt in the standalone case. Now setup_host_tool() will try to build a native tool, but it needs build_native_tool() from CrossCompile.cmake, so that also needs to be included. Finally, the native binary then fails because there's no provider for the dependency "CONFIGURE_Clang_NATIVE", so use llvm_create_cross_target to create the native environment. These few lines mirror what the lldb CMakeLists.txt does in the standalone case, so there is prior art for this. [1] https://git.openembedded.org/openembedded-core/tree/meta/recipes-devtools/clang/clang_git.bb?id=e18d697e92b55e57124e80234369d46575226386#n212 [2] https://github.com/NixOS/nixpkgs/blob/3354d448f2a26117a74638957b0131ce3da9c8c4/pkgs/development/compilers/llvm/common/tblgen.nix#L54 >From 2ff1134d1d2b9f3c207e3ebd98de922f9ef6c15a Mon Sep 17 00:00:00 2001 From: Ross Burton <[email protected]> Date: Wed, 24 Sep 2025 17:02:57 +0100 Subject: [PATCH] [clang] Support building native tools when cross-compiling standalone clang When cross-compiling the LLVM project as a whole (from llvm/), if it cannot find presupplied tools it will create a native build environment to build the tools it needs. However, when doing a standalone build of clang (that is, from clang/ and linking against an existing libLLVM) this doesn't work. Instead a _target_ binary is built which predictably then fails. The conventional workaround for this is to build the native tools in a separate native compile phase and pass the paths to the cross build, for example see OpenEmbedded[1] or Nix[2]. But we can do better! The first problem is that LLVM_USE_HOST_TOOLS is only set in the llvm/ CMakeLists.txt, so setup_host_tool() will never consider building a native binary. This can be solved by setting LLVM_USE_HOST_TOOLS based on CMAKE_CROSSCOMPILING in clang/CMakeLists.txt in the standalone case. Now setup_host_tool() will try to build a native tool, but it needs build_native_tool() from CrossCompile.cmake, so that also needs to be included. Finally, the native binary then fails because there's no provider for the dependency "CONFIGURE_Clang_NATIVE", so use llvm_create_cross_target to create the native environment. These few lines mirror what the lldb CMakeLists.txt does in the standalone case, so there is prior art for this. [1] https://git.openembedded.org/openembedded-core/tree/meta/recipes-devtools/clang/clang_git.bb?id=e18d697e92b55e57124e80234369d46575226386#n212 [2] https://github.com/NixOS/nixpkgs/blob/3354d448f2a26117a74638957b0131ce3da9c8c4/pkgs/development/compilers/llvm/common/tblgen.nix#L54 --- clang/CMakeLists.txt | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt index 1bb73599970c1..4eaa712899856 100644 --- a/clang/CMakeLists.txt +++ b/clang/CMakeLists.txt @@ -80,6 +80,12 @@ if(CLANG_BUILT_STANDALONE) include(GetErrcMessages) include(LLVMDistributionSupport) + if(CMAKE_CROSSCOMPILING) + set(LLVM_USE_HOST_TOOLS ON) + include(CrossCompile) + llvm_create_cross_target(Clang NATIVE "" Release) + endif() + set(PACKAGE_VERSION "${LLVM_PACKAGE_VERSION}") set(BUG_REPORT_URL "${LLVM_PACKAGE_BUGREPORT}" CACHE STRING "Default URL where bug reports are to be submitted.") _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
