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, 5 insertions, 4 deletions

diff --git a/compiler/rustc_codegen_llvm/src/allocator.rs b/compiler/rustc_codegen_llvm/src/allocator.rs
index 55ee6dcdf87..a2e6c7eb856 100644
--- a/compiler/rustc_codegen_llvm/src/allocator.rs
+++ b/compiler/rustc_codegen_llvm/src/allocator.rs
@@ -7,6 +7,7 @@ use rustc_middle::bug;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::{DebugInfo, OomStrategy};
 
+use crate::common::AsCCharPtr;
 use crate::llvm::{self, Context, False, Module, True, Type};
 use crate::{ModuleLlvm, attributes, debuginfo};
 
@@ -76,14 +77,14 @@ pub(crate) unsafe fn codegen(
     unsafe {
         // __rust_alloc_error_handler_should_panic
         let name = OomStrategy::SYMBOL;
-        let ll_g = llvm::LLVMRustGetOrInsertGlobal(llmod, name.as_ptr().cast(), name.len(), i8);
+        let ll_g = llvm::LLVMRustGetOrInsertGlobal(llmod, name.as_c_char_ptr(), name.len(), i8);
         llvm::set_visibility(ll_g, llvm::Visibility::from_generic(tcx.sess.default_visibility()));
         let val = tcx.sess.opts.unstable_opts.oom.should_panic();
         let llval = llvm::LLVMConstInt(i8, val as u64, False);
         llvm::LLVMSetInitializer(ll_g, llval);
 
         let name = NO_ALLOC_SHIM_IS_UNSTABLE;
-        let ll_g = llvm::LLVMRustGetOrInsertGlobal(llmod, name.as_ptr().cast(), name.len(), i8);
+        let ll_g = llvm::LLVMRustGetOrInsertGlobal(llmod, name.as_c_char_ptr(), name.len(), i8);
         llvm::set_visibility(ll_g, llvm::Visibility::from_generic(tcx.sess.default_visibility()));
         let llval = llvm::LLVMConstInt(i8, 0, False);
         llvm::LLVMSetInitializer(ll_g, llval);
@@ -115,7 +116,7 @@ fn create_wrapper_function(
         );
         let llfn = llvm::LLVMRustGetOrInsertFunction(
             llmod,
-            from_name.as_ptr().cast(),
+            from_name.as_c_char_ptr(),
             from_name.len(),
             ty,
         );
@@ -137,7 +138,7 @@ fn create_wrapper_function(
         }
 
         let callee =
-            llvm::LLVMRustGetOrInsertFunction(llmod, to_name.as_ptr().cast(), to_name.len(), ty);
+            llvm::LLVMRustGetOrInsertFunction(llmod, to_name.as_c_char_ptr(), to_name.len(), ty);
         if let Some(no_return) = no_return {
             // -> ! DIFlagNoReturn
             attributes::apply_to_llfn(callee, llvm::AttributePlace::Function, &[no_return]);