When mixing ObjC, C++ and Rust in the same binary on aarch64-apple-darwin targets (e.g. like in Firefox), lld from LLVM 15 complains about "too many personalities". This is a regression from #92845 and affects beta.

For some reason, since #92845, this code in lld is hit: https://github.com/llvm/llvm-project/blob/d30dccd21f2c3bc1ed6cd054c131436a1af548e1/lld/MachO/UnwindInfoSection.cpp#L300

Ultimately, this leads to https://github.com/llvm/llvm-project/blob/d30dccd21f2c3bc1ed6cd054c131436a1af548e1/lld/MachO/UnwindInfoSection.cpp#L378
where there are 4 personalities instead of 3:

• ___objc_personality_v0,
• ___gxx_personality_v0,
• _rust_eh_personality
• <internal>

With previous rust versions, only the first three ones would be there. It looks like the relocation that triggers the <internal> is related to the rust_eh_personality function in library/std/src/personality/gcc.rs itself.

STR:

• Create a bar.cc file with content:

#include <stdexcept>

extern "C" void qux();

void bar() { qux(); throw std::runtime_error("foo"); }

• Create a foo.m file with content:

void foo() { @try {} @finally {} }

• Create a qux.rs file with content:

#![crate_type = "staticlib"]

extern "C" {
    fn foo();
}

#[no_mangle]
pub unsafe extern "C" fn qux() {
    println!("foo");
    foo();
}

• Create a Makefile file with content:

TARGET = --target=aarch64-apple-darwin

lib.dylib: bar.o foo.o libqux.a
	clang++ -o $@ $^ -fuse-ld=lld -dynamiclib $(TARGET) -lobjc

bar.o: bar.cc
	clang++ -o $@ -c $^ $(TARGET)

foo.o: foo.m
	clang -o $@ -c $^ $(TARGET)

libqux.a: qux.rs
	rustc $^ $(TARGET)

• Get clang 15 + lld and make sure it's in your $PATH.
• Set SDKROOT to point to a macOS SDK
• Run make

This does not happen on x86_64-apple-darwin, but interestingly the list of personalities there is:

• ___objc_personality_v0,
• ___gxx_personality_v0,
• <internal>
  (no _rust_eh_personality).

With rust 1.64, the list of personalities was:

• ___objc_personality_v0,
• ___gxx_personality_v0,
• _rust_eh_personality