From 0fa86f966062a66f46b6471310d07e00b701e398 Mon Sep 17 00:00:00 2001
From: Zalathar <Zalathar@users.noreply.github.com>
Date: Sat, 2 Nov 2024 11:44:15 +1100
Subject: [PATCH] Use a dedicated safe wrapper for `LLVMRustGetHostCPUName`

---
 compiler/rustc_codegen_llvm/src/llvm/ffi.rs   |  2 +-
 compiler/rustc_codegen_llvm/src/llvm_util.rs  | 32 ++++++++++++-------
 .../rustc_llvm/llvm-wrapper/PassWrapper.cpp   |  4 +--
 3 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 5fad7583e1a..0c0e3b92e59 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -2204,7 +2204,7 @@ unsafe extern "C" {
         Desc: &mut *const c_char,
     );
 
-    pub fn LLVMRustGetHostCPUName(len: *mut usize) -> *const c_char;
+    pub fn LLVMRustGetHostCPUName(LenOut: &mut size_t) -> *const u8;
 
     // This function makes copies of pointed to data, so the data's lifetime may end after this
     // function returns.
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index 9adb1299b3d..20144824d88 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -476,23 +476,31 @@ pub(crate) fn print(req: &PrintRequest, mut out: &mut String, sess: &Session) {
     }
 }
 
-fn handle_native(name: &str) -> &str {
-    if name != "native" {
-        return name;
-    }
-
-    unsafe {
-        let mut len = 0;
+/// Returns the host CPU name, according to LLVM.
+fn get_host_cpu_name() -> &'static str {
+    let mut len = 0;
+    // SAFETY: The underlying C++ global function returns a `StringRef` that
+    // isn't tied to any particular backing buffer, so it must be 'static.
+    let slice: &'static [u8] = unsafe {
         let ptr = llvm::LLVMRustGetHostCPUName(&mut len);
-        str::from_utf8(slice::from_raw_parts(ptr as *const u8, len)).unwrap()
+        assert!(!ptr.is_null());
+        slice::from_raw_parts(ptr, len)
+    };
+    str::from_utf8(slice).expect("host CPU name should be UTF-8")
+}
+
+/// If the given string is `"native"`, returns the host CPU name according to
+/// LLVM. Otherwise, the string is returned as-is.
+fn handle_native(cpu_name: &str) -> &str {
+    match cpu_name {
+        "native" => get_host_cpu_name(),
+        _ => cpu_name,
     }
 }
 
 pub(crate) fn target_cpu(sess: &Session) -> &str {
-    match sess.opts.cg.target_cpu {
-        Some(ref name) => handle_native(name),
-        None => handle_native(sess.target.cpu.as_ref()),
-    }
+    let cpu_name = sess.opts.cg.target_cpu.as_deref().unwrap_or_else(|| &sess.target.cpu);
+    handle_native(cpu_name)
 }
 
 /// The list of LLVM features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,
diff --git a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
index 3b7dc6de825..245edde2768 100644
--- a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
@@ -382,9 +382,9 @@ extern "C" void LLVMRustGetTargetFeature(LLVMTargetMachineRef TM, size_t Index,
   *Desc = Feat.Desc;
 }
 
-extern "C" const char *LLVMRustGetHostCPUName(size_t *len) {
+extern "C" const char *LLVMRustGetHostCPUName(size_t *OutLen) {
   StringRef Name = sys::getHostCPUName();
-  *len = Name.size();
+  *OutLen = Name.size();
   return Name.data();
 }