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> is still mostly dependent on C (even C++ really, due to LLVM/Clang) I'm not following the assertion that compilation with LLVM/Clang introduces a C++ depende

> is still mostly dependent on C (even C++ really, due to LLVM/Clang) I'm not following the assertion that compilation with LLVM/Clang introduces a C++ dependency on the language being compiled (Rust here).

ziandrome22 3y ago
You will need to generate code for the target which means LLVM/Clang (a C++ project) must support at the very least some amount of codegen for that target.
- steveklabnik 3y ago
  You can use the cranelift backend, written in Rust, if you prefer. Nothing about LLVM being the best choice by default has to do with the choice of implementation language.
  - Vecr 3y ago
    Or more likely for something that needs to be high performance mrustc, but you obviously have to be careful there.
    - steveklabnik 3y ago
      mrustc is written in C++, so I don't see how it's a counter to what the parent is proposing. I also don't know anything about mrustc's performance characteristics, I didn't think performance was a goal, but it's also been a while since I've checked in on it.
      - Vecr 3y ago
        Oh right, I don't even know if there's a C compiler that's not written in C++ that can compile the output of mrustc anyway, so there's that.
AYoung010 3y ago
I think the assertion is based on the fact that LLVM is written in C++. Doesn’t directly introduce a C++ dependency to the kernel, but it does introduce it to the toolchain.
- kibwen 3y ago
  But rustc is a cross-compiler, you only need a C compiler for one platform and you get a Rust compiler for all platforms. And it's not like LLVM is doing anything that fundamentally prevents it from being written in Rust (see also the Cranelift backend for Rust, written in Rust). I'm still not quite sure what the concrete concern is. Can you elaborate?
- fleventynine 3y ago
  Modern GCC is also primarily written in C++, and has had C++ deps since 2013: https://github.com/gcc-mirror/gcc/blob/master/gcc/input.cc https://github.com/gcc-mirror/gcc/blob/master/gcc/input.cc
vlovich123 3y ago
This comment confuses me. > In August 2012, the GCC steering committee announced that GCC now uses C++ as its implementation language.[57] This means that to build GCC from sources, a C++ compiler is required that understands ISO/IEC C++03 standard. > On May 18, 2020, GCC moved away from ISO/IEC C++03 standard to ISO/IEC C++11 standard (i.e. needed to compile, bootstrap, the compiler itself; by default it however compiles later versions of C++).[58] So for the past >10 years, gcc and clang have both had a C++ dependency. What is unique about LLVM/Clang here?
- jjtheblunt 3y ago
  If I understand what you’re considering, it’s that the compiler itself may have been compiled from C++ sources, so dependencies in that accounting scheme derive from transitive closure. Alternatively i consider a compiler might only be presented as a binary, with no visibility as to its own source code, so i consider in that case just a Rust program and a binary that compiles it to a native binary linking with binary object files also of unspecified source code languages.
  - vlovich123 3y ago
    Sorry, we’re in agreement. My reply was meant to reply to the parent claiming there’s a C++ dependency in the tool chain when building everything from source - that’s true for the Linux kernel today since building GCC requires a C++ compiler as well.

ziandrome22 3y ago

You will need to generate code for the target which means LLVM/Clang (a C++ project) must support at the very least some amount of codegen for that target.

steveklabnik 3y ago
You can use the cranelift backend, written in Rust, if you prefer. Nothing about LLVM being the best choice by default has to do with the choice of implementation language.
- Vecr 3y ago
  Or more likely for something that needs to be high performance mrustc, but you obviously have to be careful there.
  - steveklabnik 3y ago
    mrustc is written in C++, so I don't see how it's a counter to what the parent is proposing. I also don't know anything about mrustc's performance characteristics, I didn't think performance was a goal, but it's also been a while since I've checked in on it.
    - Vecr 3y ago
      Oh right, I don't even know if there's a C compiler that's not written in C++ that can compile the output of mrustc anyway, so there's that.

AYoung010 3y ago

I think the assertion is based on the fact that LLVM is written in C++. Doesn’t directly introduce a C++ dependency to the kernel, but it does introduce it to the toolchain.

kibwen 3y ago
But rustc is a cross-compiler, you only need a C compiler for one platform and you get a Rust compiler for all platforms. And it's not like LLVM is doing anything that fundamentally prevents it from being written in Rust (see also the Cranelift backend for Rust, written in Rust). I'm still not quite sure what the concrete concern is. Can you elaborate?
fleventynine 3y ago
Modern GCC is also primarily written in C++, and has had C++ deps since 2013: https://github.com/gcc-mirror/gcc/blob/master/gcc/input.cc https://github.com/gcc-mirror/gcc/blob/master/gcc/input.cc

vlovich123 3y ago

This comment confuses me. > In August 2012, the GCC steering committee announced that GCC now uses C++ as its implementation language.[57] This means that to build GCC from sources, a C++ compiler is required that understands ISO/IEC C++03 standard. > On May 18, 2020, GCC moved away from ISO/IEC C++03 standard to ISO/IEC C++11 standard (i.e. needed to compile, bootstrap, the compiler itself; by default it however compiles later versions of C++).[58] So for the past >10 years, gcc and clang have both had a C++ dependency. What is unique about LLVM/Clang here?

jjtheblunt 3y ago
If I understand what you’re considering, it’s that the compiler itself may have been compiled from C++ sources, so dependencies in that accounting scheme derive from transitive closure. Alternatively i consider a compiler might only be presented as a binary, with no visibility as to its own source code, so i consider in that case just a Rust program and a binary that compiles it to a native binary linking with binary object files also of unspecified source code languages.
- vlovich123 3y ago
  Sorry, we’re in agreement. My reply was meant to reply to the parent claiming there’s a C++ dependency in the tool chain when building everything from source - that’s true for the Linux kernel today since building GCC requires a C++ compiler as well.