Definition __ZTSPKDu in itanium-base.exp is used for -export_symbol but is really undefined

[mulle-nat]

Bugzilla Link	43749
Resolution	INVALID
Resolved on	Jun 01, 2020 12:53
Version	9.0
OS	MacOS X
CC	@ldionne,@mclow

Extended Description

This happens when building on MacOS 10.13. I suppose some parts of the code gets #ifdef-ed out, but the symbollist isn't, that is passed to the linker.
This list is in lib/itanium-base.exp and used as input for -exported_symbols_list.

Now Apple's linker decided in its wisdom, that missing actual symbols are an error (and not a warning, what would be sane) and the build aborts.

All affected symbols are of the form _Z.*du. If I remove them before building things work out OK.

[mulle-nat]

assigned to @ldionne

[llvmbot]

I also have this problem. BTW, is it OK to have itanium symbols on x86_64 arch? Itanium is kind of different thing isn't it?

[ldionne]

What compiler are you using? I'm guessing you're using a fairly old Clang.

The issue is that the compiler emits type information for fundamental types in libc++abi, and your compiler doesn't know about char8_t yet, so it doesn't emit the type information for those. libc++abi tries to export these symbols and it fails to do so, because they haven't been generated in the dylib by the compiler.

Getting a linker error is quite nice, because otherwise you'd be producing a libc++abi.dylib that doesn't work properly at runtime (say if you try to use typeid(char8_t) in your program).

The fix is to use a recent Clang when building libc++ and libc++abi.

[outtersg]

(duplicate of #42070, where @ldionne's other comment is of great help to "bootstrap" on unmaintained platforms)