Hacker News Reader

Comment by davidbalbert | Hacker News Reader

The article references a few compiler extensions: __builtin_xnu_type_signature, __builtin_xnu_type_summary, and the xnu_usage_semantics attribute.

I can see references to these builtins in the latest xnu source[1], but not in upstream llvm[2], or Apple's forks of llvm[3] and clang[4].

It's been possible to build your own XNU[5] for a long time. Is that still possible now?

  [1]: https://github.com/apple-oss-distributions/xnu
  [2]: https://github.com/llvm/llvm-project
  [3]: https://github.com/apple-oss-distributions/llvmCore
  [4]: https://github.com/apple-oss-distributions/clang
  [5]: https://kernelshaman.blogspot.com/2021/02/building-xnu-for-macos-112-intel-apple.html

View on HN

I believe Apple’s toolchain ship with this.

You're right. Just compiled the following program with clang from Xcode 14 (Apple clang version 14.0.0 (clang-1400.0.29.102)) without issue.

  #include <stdio.h>
  
  struct foo {
   uintptr_t p __attribute__((xnu_usage_semantics("pointer")));
  };
  
  int main() {
   struct foo f = { 100 };
  
   printf("%lu\n", f.p);
   return 0;
  }

Doesn't seem -Wxnu-typed-allocators (which I forgot to mention above) is present in my version. Didn't test the others.

I also just realized that the latest tagged release of https://github.com/apple-oss-distributions/clang is 800.0.38, my clang is reporting 1400.0.29.102. Is Apple no longer releasing the source for their compilers?

The article sounded to me like Apple had a private fork with extra tooling to help with their kernel work.

Heh... and it was just a few weeks ago I was assured that all of the platform internals were fully open sourced. ;-)

I doubt that they have opened the custom C compiler used in iBoot for example.

https://support.apple.com/guide/security/memory-safe-iboot-i...

They have not.

A lot of the internals are, but certainly not all. And they always lag behind with what is currently released, sometimes by several months.

It's funny, that's pretty much what I said...

The clang that ships in Xcode uses fake version numbers, but yes, some of it remains proprietary.

Apple never did release everything that their compilers do, that is why cppreference has a column for Apple's clang, and why watchOS can use bitcode as binary format, even though the official LLVM bitcode isn't stable.

Reply on news.ycombinator.com