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Make LLVMRustGetOrInsertGlobal always return a GlobalVariable

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`Module::getOrInsertGlobal` returns a `Constant*`, which is a super
class of `GlobalVariable`, but if the given type doesn't match an
existing declaration, it returns a bitcast of that global instead.
This causes UB when we pass that to `LLVMGetVisibility` which
unconditionally casts the opaque argument to a `GlobalValue*`.

Instead, we can do our own get-or-insert without worrying whether
existing types match exactly. It's not relevant when we're just trying
to get/set the linkage and visibility, and if types are needed we can
bitcast or error nicely from `rustc_codegen_llvm` instead.
This commit is contained in:
Josh Stone 2021-11-19 19:33:29 -08:00
parent a77da2d454
commit 023cc968e1
2 changed files with 45 additions and 1 deletions
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12
compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
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@ -124,8 +124,18 @@ extern "C" LLVMValueRef LLVMRustGetOrInsertFunction(LLVMModuleRef M,
extern "C" LLVMValueRef
LLVMRustGetOrInsertGlobal(LLVMModuleRef M, const char *Name, size_t NameLen, LLVMTypeRef Ty) {
Module *Mod = unwrap(M);
StringRef NameRef(Name, NameLen);
return wrap(unwrap(M)->getOrInsertGlobal(NameRef, unwrap(Ty)));
// We don't use Module::getOrInsertGlobal because that returns a Constant*,
// which may either be the real GlobalVariable*, or a constant bitcast of it
// if our type doesn't match the original declaration. We always want the
// GlobalVariable* so we can access linkage, visibility, etc.
GlobalVariable *GV = Mod->getGlobalVariable(NameRef, true);
if (!GV)
GV = new GlobalVariable(*Mod, unwrap(Ty), false,
GlobalValue::ExternalLinkage, nullptr, NameRef);
return wrap(GV);
}
extern "C" LLVMValueRef