cg_llvm: Make the LLVM version-check bindings safe

compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs

@@ -97,7 +97,7 @@ pub(crate) mod Enzyme_AD {
     use rustc_session::filesearch;
 
     use super::{CConcreteType, CTypeTreeRef, Context};
-    use crate::llvm::{EnzymeTypeTree, LLVMRustVersionMajor};
+    use crate::llvm::{self, EnzymeTypeTree};
 
     type EnzymeSetCLBoolFn = unsafe extern "C" fn(*mut c_void, u8);
     type EnzymeSetCLStringFn = unsafe extern "C" fn(*mut c_void, *const c_char);
@@ -434,7 +434,7 @@ pub(crate) mod Enzyme_AD {
         }
 
         fn get_enzyme_path(sysroot: &Sysroot) -> Result<String, EnzymeLibraryError> {
-            let llvm_version_major = unsafe { LLVMRustVersionMajor() };
+            let llvm_version_major = llvm::LLVMRustVersionMajor();
 
             let path_buf = sysroot
                 .all_paths()

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -894,7 +894,11 @@ unsafe extern "C" {
         SLen: c_uint,
     ) -> MetadataKindId;
 
-    pub(crate) fn LLVMGetVersion(major: &mut c_uint, minor: &mut c_uint, patch: &mut c_uint);
+    /// Gets the actual version of LLVM that we are linked to at runtime.
+    ///
+    /// # Safety
+    /// Can be called without initializing LLVM.
+    pub(crate) safe fn LLVMGetVersion(major: &mut c_uint, minor: &mut c_uint, patch: &mut c_uint);
 
     pub(crate) fn LLVMDisposeTargetMachine(T: ptr::NonNull<TargetMachine>);
 
@@ -2176,9 +2180,9 @@ unsafe extern "C" {
     /// Returns the LLVM major version that the compiler was built with.
     ///
     /// Note that this is hard-coded as `LLVM_VERSION_MAJOR` when `RustWrapper.cpp` is built. This
-    /// could be different than what the runtime LLVM library reports in `LLVMGetVersion`, so we
+    /// could be different than what the runtime LLVM library reports in [`LLVMGetVersion`], so we
     /// assert their equality in `configure_llvm`.
-    pub(crate) fn LLVMRustVersionMajor() -> u32;
+    pub(crate) safe fn LLVMRustVersionMajor() -> u32;
 
     /// Add LLVM module flags.
     ///

compiler/rustc_codegen_llvm/src/llvm/offload_ffi.rs

@@ -14,7 +14,7 @@ use rustc_fs_util::path_to_c_string;
 use rustc_session::config::host_tuple;
 use rustc_session::filesearch;
 
-use crate::llvm::LLVMRustVersionMajor;
+use crate::llvm;
 
 pub(crate) struct RustOffloadWrapper {
     LLVMRustBundleImages: LLVMRustBundleImagesFn,
@@ -119,7 +119,7 @@ impl RustOffloadWrapper {
     fn get_offload_and_lld_paths(
         sysroot: &rustc_session::config::Sysroot,
     ) -> Result<(PathBuf, Option<PathBuf>), RustOffloadLibraryError> {
-        let llvm_version_major = unsafe { LLVMRustVersionMajor() };
+        let llvm_version_major = llvm::LLVMRustVersionMajor();
         let mut searched = Vec::new();
 
         for root in sysroot.all_paths() {

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -459,15 +459,13 @@ pub(crate) fn print_version() {
     println!("LLVM version: {major}.{minor}.{patch}");
 }
 
+/// Returns the version of LLVM that we are actually linked to at runtime.
 pub(crate) fn get_version() -> (u32, u32, u32) {
-    // Can be called without initializing LLVM
-    unsafe {
-        let mut llvm_major = 0;
-        let mut llvm_minor = 0;
-        let mut llvm_patch = 0;
-        llvm::LLVMGetVersion(&mut llvm_major, &mut llvm_minor, &mut llvm_patch);
-        (llvm_major, llvm_minor, llvm_patch)
-    }
+    let mut llvm_major = 0;
+    let mut llvm_minor = 0;
+    let mut llvm_patch = 0;
+    llvm::LLVMGetVersion(&mut llvm_major, &mut llvm_minor, &mut llvm_patch);
+    (llvm_major, llvm_minor, llvm_patch)
 }
 
 pub(crate) fn print_passes() {