558553272d
Stop emitting the `dso_local` LLVM attribute for external symbols under the static relocation model on macOS. This matches Clang's behavior:973cb2c326/clang/lib/CodeGen/CodeGenModule.cpp (L1038-L1040)
Even if `dso_local` were properly supported in this way on macOS, it seems incorrect to add this annotation as liberally as we did. The `dso_local` annotation is for symbols that ultimately end up in the same linkage unit, but we were adding this annotation even for `static` values inside `extern` blocks marked with `#[link(type="framework")]`, which should be considered dynamically linked. Note that Clang likewise avoids emitting `dso_local` for `dllimport` symbols:973cb2c326/clang/lib/CodeGen/CodeGenModule.cpp (L1005-L1007)
This issue caused breakage in the `ring` crate, which links to a symbol defined in `Security.framework` that ultimately resolves to address `0x0`:b94d61e044/src/rand.rs (L390)
For this symbol, the use of `dso_local` causes LLVM to emit a relocation of type `X86_64_RELOC_SIGNED`, which is a 32-bit signed PC-relative offset. If the binary is large enough, `0x0` might be out of range, and the link will fail. Avoiding `dso_local` causes LLVM to use the GOT instead, emitting a relocation of type `X86_64_RELOC_GOT_LOAD`, which will properly handle the large offset and cause the link to succeed. As a side note, the static relocation model is effectively deprecated for security reasons on macOS, as it prohibits PIE. It's also completely unsupported on Apple Silicon, so I don't think it's worth going to the effort of properly supporting this model on that platform.