Rollup merge of #132260 - Zalathar:type-safe-cast, r=compiler-errors

cg_llvm: Use a type-safe helper to cast `&str` and `&[u8]` to `*const c_char`

In `rustc_codegen_llvm` there are many uses of `.as_ptr().cast()` to convert a string or byte-slice to `*const c_char`, which then gets passed through FFI.

This works, but is fragile, because there's nothing constraining the pointer cast to actually be from `u8` to `c_char`. If the original value changes to something else that has an `as_ptr` method, or the context changes to expect something other than `c_char`, the cast will silently do the wrong thing.

By making the cast more explicit via a helper method, we can be sure that it will either perform the intended cast, or fail at compile time.

1 files changed, 4 insertions, 3 deletions

diff --git a/compiler/rustc_codegen_llvm/src/declare.rs b/compiler/rustc_codegen_llvm/src/declare.rs
index 33258cb46fa..d338c848754 100644
--- a/compiler/rustc_codegen_llvm/src/declare.rs
+++ b/compiler/rustc_codegen_llvm/src/declare.rs
@@ -20,6 +20,7 @@ use smallvec::SmallVec;
 use tracing::debug;
 
 use crate::abi::{FnAbi, FnAbiLlvmExt};
+use crate::common::AsCCharPtr;
 use crate::context::CodegenCx;
 use crate::llvm::AttributePlace::Function;
 use crate::llvm::Visibility;
@@ -41,7 +42,7 @@ fn declare_raw_fn<'ll>(
 ) -> &'ll Value {
     debug!("declare_raw_fn(name={:?}, ty={:?})", name, ty);
     let llfn = unsafe {
-        llvm::LLVMRustGetOrInsertFunction(cx.llmod, name.as_ptr().cast(), name.len(), ty)
+        llvm::LLVMRustGetOrInsertFunction(cx.llmod, name.as_c_char_ptr(), name.len(), ty)
     };
 
     llvm::SetFunctionCallConv(llfn, callconv);
@@ -68,7 +69,7 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
     /// return its Value instead.
     pub(crate) fn declare_global(&self, name: &str, ty: &'ll Type) -> &'ll Value {
         debug!("declare_global(name={:?})", name);
-        unsafe { llvm::LLVMRustGetOrInsertGlobal(self.llmod, name.as_ptr().cast(), name.len(), ty) }
+        unsafe { llvm::LLVMRustGetOrInsertGlobal(self.llmod, name.as_c_char_ptr(), name.len(), ty) }
     }
 
     /// Declare a C ABI function.
@@ -209,7 +210,7 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
     /// Gets declared value by name.
     pub(crate) fn get_declared_value(&self, name: &str) -> Option<&'ll Value> {
         debug!("get_declared_value(name={:?})", name);
-        unsafe { llvm::LLVMRustGetNamedValue(self.llmod, name.as_ptr().cast(), name.len()) }
+        unsafe { llvm::LLVMRustGetNamedValue(self.llmod, name.as_c_char_ptr(), name.len()) }
     }
 
     /// Gets defined or externally defined (AvailableExternally linkage) value by