[PATCH] D93164: [AST] Add generator for source location introspection

Tue Jan 18 14:40:10 PST 2022

smeenai added a comment.

In D93164#3252509 <https://reviews.llvm.org/D93164#3252509>, @lancethepants wrote:

> In D93164#3250945 <https://reviews.llvm.org/D93164#3250945>, @andrew-wja wrote:
>
>> In D93164#3048130 <https://reviews.llvm.org/D93164#3048130>, @lancethepants wrote:
>>
>>> In D93164#2653067 <https://reviews.llvm.org/D93164#2653067>, @mgorny wrote:
>>>
>>>> This change breaks cross-compilation now, as it tries running an executable built for the target system:
>>>>
>>>>   FAILED: tools/clang/lib/Tooling/ASTNodeAPI.json 
>>>>   cd /home/mgorny/llvm-project/build.arm64/tools/clang/lib/Tooling && /home/mgorny/llvm-project/build.arm64/bin/clang-ast-dump --skip-processing=0 --astheader=/home/mgorny/llvm-project/build.arm64/tools/clang/lib/Tooling/ASTTU.cpp -I /home/mgorny/llvm-project/build.arm64/lib/clang/13.0.0/include -I /home/mgorny/llvm-project/llvm/../clang/include -I /home/mgorny/llvm-project/build.arm64/tools/clang/include -I /home/mgorny/llvm-project/build.arm64/include -I /home/mgorny/llvm-project/llvm/include -I /sysroot/arm64/usr/include/c++/v1 -I /usr/lib/clang/11.0.1/include -I /sysroot/arm64/usr/include --json-output-path /home/mgorny/llvm-project/build.arm64/tools/clang/lib/Tooling/ASTNodeAPI.json
>>>>   /bin/sh: /home/mgorny/llvm-project/build.arm64/bin/clang-ast-dump: Exec format error
>>>>
>>>> I guess you can look at TableGens how to correctly generate and use host executables.
>>>
>>> I am now running into this error now that clang13 has released.  I cannot figure a way around this. I do not see any cmake options similar to the tablegens that allow you to specify the binary for the build system.  Am I missing something or is clang13 just broken for cross compilation?
>>
>> Another confirmation that this change has broken cross compilation. I have tried setting both `-DCLANG_TOOLING_BUILD_AST_INTROSPECTION=OFF` and `-DCMAKE_CROSSCOMPILING=ON` separately and in combination. This means that LLVM cannot be cross compiled for AArch64, which is a pretty serious problem!
>
> So I did find a solution. Maybe somewhere else in the forums or on irc. Can't remember for sure.
>
> -DCMAKE_SYSTEM_NAME="Linux"
> Add this is well to your cmake invocation. For some reason this triggers in cmake that we are cross-compiling. Why -DCMAKE_CROSSCOMPILING=ON is insufficient I have no idea why. I'm compiling on linux for linux, didn't think I'd need it.  Kind of unintuitive, but that should hopefully get you going.

I believe the relevant bit of CMake logic is https://gitlab.kitware.com/cmake/cmake/-/blob/a2e42a577b08dc65ba801e18e5c8be163df83455/Modules/CMakeDetermineSystem.cmake#L136-158. If `CMAKE_SYSTEM_NAME` isn't set, it'll set `CMAKE_CROSSCOMPILING` to `FALSE` internally.

Repository:
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https://reviews.llvm.org/D93164