Wrong return type of extern functions

[honzasp]

Hi,

I was trying to use the LLVM C bindings from Rust, but I ran into a mysterious error when I tried to use LLVMGetTypeKind. The Rust program is like this:

#[allow(cstack)];
use std::libc::{c_uint};

pub enum Context_opaque {}
pub type ContextPtr = *Context_opaque;
pub enum Type_opaque {}
pub type TypePtr = *Type_opaque;

#[repr(C)]
pub enum LLVMTypeKind {
  LLVMVoidTypeKind,
  LLVMHalfTypeKind,
  LLVMFloatTypeKind,
  LLVMDoubleTypeKind,
  LLVMX86_FP80TypeKind,
  LLVMFP128TypeKind,
  LLVMPPC_FP128TypeKind,
  LLVMLabelTypeKind,
  LLVMIntegerTypeKind,
  LLVMFunctionTypeKind,
  LLVMStructTypeKind,
  LLVMArrayTypeKind,
  LLVMPointerTypeKind,
  LLVMVectorTypeKind,
  LLVMMetadataTypeKind,
  LLVMX86_MMXTypeKind
}

#[link_args = "-lLLVMCore -lLLVMSupport"]
extern {
  pub fn LLVMContextCreate() -> ContextPtr;
  pub fn LLVMContextDispose(c: ContextPtr);
  pub fn LLVMGetTypeKind(t: TypePtr) -> LLVMTypeKind;
  pub fn LLVMIntTypeInContext(c: ContextPtr, bits: c_uint) -> TypePtr;
}

fn main() {
  unsafe {
    let ctx_ptr = LLVMContextCreate();
    let int32_ptr = LLVMIntTypeInContext(ctx_ptr, 32);
    let kind = LLVMGetTypeKind(int32_ptr); // boom!
    println!("{}", kind as uint);
    LLVMContextDispose(ctx_ptr);
  }
}

When compiled and executed, LLVM crashes with

Unhandled TypeID.
UNREACHABLE executed at Core.cpp:164!
Aborted (core dumped)

After some investigation, I made rustc emit LLVM bitcode and found something strange:

declare void @LLVMGetTypeKind(%enum.LLVMTypeKind* sret, %enum.Type_opaque*) unnamed_addr

call void @LLVMGetTypeKind(%enum.LLVMTypeKind* sret %kind, %enum.Type_opaque* %11)

rustc declared the LLVMGetTypeKind function with wrong parameters, so the function, when called, got a pointer to unitialized value on stack instead of a ContextRef.

I tried to declare LLVMGetTypeKind as a function returning c_uint and everything worked well (it is probably the reason why rustc's LLVM bindings declare LLVMTypeKind as a series of static variables).

Is this a bug or a feature? If it is a feature, it is worth documenting! :)

[alexcrichton]

This may be related to #10308, cc @jld @nikomatsakis

[nikomatsakis]

Bug in ABI code, definitely -- @honzasp what target architecture / operating system?

[honzasp]

I wasn't sure, because the rustc's own LLVM bindings (in
rust/src/librustc/lib/llvm.rs) declare all C enums from the API as Rust
enums, except for LLVMTypeKind, which is defined as a u32 and the
variants are specified as static variables. ("blame"-ing the file on GitHub
points to commit a5ddc00, which in turn references #5347).

As for the version:

~ $ rustc --version
rustc 0.9-pre (85a1eff 2013-11-21 06:16:49 -0800)
host: i686-unknown-linux-gnu

[jld]

I'm pretty sure this is a duplicate of bug #10308, which will soon be fixed by PR #10652.

[jld]

Should be fixed on master now.

#10684, which changes rustc's own LLVM bindings to use an enum for TypeKind like the example at the top of this issue, passed local tests on i686-unknown-linux-gnu and is now in the bors queue.