Clang `__builtin_strlen` is expanded with the wrong calling convention.

CHERIoT-Platform / llvm-project

Fork of LLVM adding CHERIoT, based on the CHERI LLVM fork

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Clang `__builtin_strlen` is expanded with the wrong calling convention. #29

Closed davidchisnall closed 5 months ago

davidchisnall commented 5 months ago

The std::string constructor calls a strlen builtin. This ends up being expanded to a strlen call without the matching calling convention and so results in link failures.

davidchisnall commented 5 months ago

There are two related issues here:

Clang does not put the right calling convention in this builtin.
Clang does not give it the right mangled name.

Clang can give it whatever name you want if you provide a prototype here, so I believe the right solution is to treat these as separate bugs and:

Make clang use the CHERIoT libcalls calling convention for all builtins that are expanded in the front end.
Add a prototype in cdefs.h that does the right thing for the builtin.