Cross compilation - C++ header inclusion

[naveens007]

I need to generate the class diagrams for code base that I normally cross compiler using a Google gn based build system.
The cross compile command (using clang 15.0.4) works OK but not compile_command.json that I generated with -MJ option and fed to clang-uml

The diagram generation fails because C++ map header cannot be found. Is there a way to work around ?

**ERROR: Failed to generate class diagram 'ArkTS' due to following issues:

• [FATAL] xxx/xxxx/myHeader.h:19: 'map' file not found**

[bkryza]

@naveens007 The error basically says that Clang cannot find std header. If you're on Linux/macos, try adding --query-driver . to the clang-uml command line invocation which will ask whatever compiler is used in compile_command.json to add it's system include paths to the compilation database.

If this doesn't work, you will have to add them manually using --add-compile-flags -isystemYOURSYSTEMPATH.

If this still doesn't work please try to share some more information (your OS, at least 1 entry from your compile_commands.json, your .clang-uml config file).

[naveens007]

Thanks for prompt response. The --query-driver option helps to get past the issue but I ran into other issues with my target headers e.g.

 - [ERROR] /home/xxxx/ohos/tools/out/llvm-install/include/libcxx-ohos/include/c++/v1/cstddef:50: no member named 'nullptr_t' in the global namespace
 - [ERROR] /home/xxx/ohos/tools/out/llvm-install/include/libcxx-ohos/include/c++/v1/__type_traits/is_null_pointer.h:24: use of undeclared identifier 'nullptr_t'; did you mean 'nullptr'?
 - [ERROR] /home/xxxx/ohos/tools/out/llvm-install/include/libcxx-ohos/include/c++/v1/__type_traits/is_null_pointer.h:24: template argument for template type parameter must be a type

My compile_commands.json has huge entries , so will not be able to share. What is clang-uml trying to do internally ? It might help me troubleshoot.

[bkryza]

With respect to compilation flags clang-uml uses similar method as clang-tidy or clangd, basically it takes the compilation flags from the compilation database and passes it to Clang, which then parses the sources and creates AST, which is then used by clang-uml to generate the diagrams.

If you call --query-driver . it calls the compiler specified in compile_commands.json to ask it what are it's system include paths and adds them to the compilations database right after argv[0] (i.e. the compiler path).

Unless Clang can parse the sources, clang-uml won't be able to generate any diagrams. Unfortunately it is very hard sometimes to figure out the compilation flags when cross-compiling, however if your are able to use for instance clang-tidy on your code, than it should be possible, but you'll have to figure out the paths and other compilation flags if necessary.

There was an issue #292 some time ago, where someone was trying to use it for embedded C++ toolchain and there was a lot of flags that were needed to be added...