[clang] Polymorphic Cleanup type is moved despite not being POD types #156607
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…types Clang has a number of Cleanup types used in exception handling, these are presumed to be POD types that can be memmoved as needed, however this is not correct by default on platforms with pointer authentication that make vtable pointers address discriminated. This PR mitigates this problem by introducing a LLVM_MOVABLE_POLYMORPHIC_TYPE macro that can be used to annotate polymorphic types that are required to be movable, to override the use of address discrimination of the vtable pointer.
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Not sure who should be looking at the Compiler.h change? |
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Not really sure I get the motivation/what is happening here, but I don't know if there is a better person to review? Perhaps @efriedma-quic can give it a quick double-check as well?
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I've reviewed other changes here recently (#152866). The code is playing some weird games with memory allocation, using an std::vector as an arena. Probably there's some better way to write this. Strictly speaking, it's undefined behavior to memmove a polymorphic class. But this is how it works for now. Maybe worth leaving a comment explaining this.
Otherwise LGTM
If you build clang targeting arm64e, pointer authentication means vtable pointers are not memcopyable by default. The fix itself is trivial, I'm more concerned about people being ok with the location of the macro |
Clang as a number of Cleanup types used in exception handling, these are presumed to be POD types that can be memmoved as needed, however this is not correct by default on platforms with pointer authentication that make vtable pointers address discriminated.
This PR mitigates this problem by introducing a LLVM_MOVABLE_POLYMORPHIC_TYPE macro that can be used to annotate polymorphic types that are required to be movable, to override the use of address discrimination of the vtable pointer.