Zig Bindgen - references

[kassane]

Previously I've been working with cbindgen which transpiles rust code into other languages, commonly used for C. However I've added zig support.

During this experiment I realized that zig can read mangled functions in both C++ and Rust (in the same way as c++filt) with the help of lld it can demangling functions (linked to libc++ + libunwind).

The best thing is the possibility of static linking in libraries written in these languages. (e.g. incubator-opendal w/ zig binding and zFFI)

• Support generation of Zig bindings mozilla/cbindgen#732 (comment)
• FFI Gen Feature oven-sh/bun#591 (comment)
• Enchanced support kassane/zFFI#2 (progress report - cbindgen-fork)
• Zig Support swig/swig#2471
• Zig Binding doesn't work with static libopendal_c apache/opendal#2471 (comment)

Another Reference

• Zig codegen Vexu/arocc#448

[lassade]

Very interesting! I will give a look into it but I'm maily interested in c++

one of my ideas with c2z is to have a copy of the memory model of c++ classes and structures in the zig side so we can just access them without the need to use opaque pointers

[kassane]

I don't know if it would be possible to retrieve the name of the translated functions using @extern to rename mangled functions and namespace.

Making it shorter, it is a possible alternative:

- extern fn @"_Z9enumerateRNSt3__16vectorIhNS_9allocatorIhEEEEm"(out_buf: *cpp.Vector(u8), count: usize) bool;
- pub const enumerate = @"_Z9enumerateRNSt3__16vectorIhNS_9allocatorIhEEEEm";
+ pub const enumerate = @extern(*const fn (out_buf: *cpp.Vector(u8), count: usize) bool, .{ .name = "_Z9enumerateRNSt3__16vectorIhNS_9allocatorIhEEEEm" });

---

I remember partially translating a C solution for demangling C++ and Rust functions. Original project used in mold linker is updated to v0 mangling, not C++ compatible.

https://github.com/kassane/rsDemangle-zig (legacy mangling, c++ compatible) based in old gist version.

[kassane]

Mangling for x86/x86_64 ABI:

abi_tag

• https://releases.llvm.org/16.0.0/tools/clang/docs/ItaniumMangleAbiTags.html
• http://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangle.abi-tag - GNU

sample

#include <vector>

__attribute__((abi_tag("cxx11")))
bool enumerate(std::vector<uint8_t>& out_buf, size_t count);

output

$>objdump -x c013_cpp_vector.obj | grep 'enumerate'
[924](sec  1)(fl 0x00)(ty   20)(scl   2) (nx 0) 0x0000000000000000 _Z9enumerateB5cxx11RNSt3__16vectorIhNS_9allocatorIhEEEEy
00000000000000c4 IMAGE_REL_AMD64_SECREL  _Z9enumerateB5cxx11RNSt3__16vectorIhNS_9allocatorIhEEEEy
00000000000000c8 IMAGE_REL_AMD64_SECTION  _Z9enumerateB5cxx11RNSt3__16vectorIhNS_9allocatorIhEEEEy
0000000000000180 IMAGE_REL_AMD64_SECREL  _Z9enumerateB5cxx11RNSt3__16vectorIhNS_9allocatorIhEEEEy
0000000000000184 IMAGE_REL_AMD64_SECTION  _Z9enumerateB5cxx11RNSt3__16vectorIhNS_9allocatorIhEEEEy
$> objdump -x c013_cpp_vector.o| grep 'enumerate'                                      
0000000000000000 g     F .text  00000000000000b9 _Z9enumerateB5cxx11RNSt3__16vectorIhNS_9allocatorIhEEEEm

Z9enumerateB5cxx11RNSt3__16vectorIhNS_9allocatorIhEEEEm | => cxx11 tag added

GNU x LLVM x MSVC

• Policies/Binary Compatibility - KDE
• MSVC compat - LLVM
• Microsoft C++ Name Mangling Scheme

Issue related

• Different mangled name for template specialization for clang and gcc llvm/llvm-project#62765
• Can't build a working DLL with cargo on Windows dtolnay/cxx#1153