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, 6 insertions, 5 deletions

diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index bf77fc56d08..e68ba96f14f 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/compiler/rustc_codegen_llvm/src/back/write.rs
@@ -34,6 +34,7 @@ use crate::back::owned_target_machine::OwnedTargetMachine;
 use crate::back::profiling::{
     LlvmSelfProfiler, selfprofile_after_pass_callback, selfprofile_before_pass_callback,
 };
+use crate::common::AsCCharPtr;
 use crate::errors::{
     CopyBitcode, FromLlvmDiag, FromLlvmOptimizationDiag, LlvmError, UnknownCompression,
     WithLlvmError, WriteBytecode,
@@ -596,9 +597,9 @@ pub(crate) unsafe fn llvm_optimize(
             llvm_selfprofiler,
             selfprofile_before_pass_callback,
             selfprofile_after_pass_callback,
-            extra_passes.as_ptr().cast(),
+            extra_passes.as_c_char_ptr(),
             extra_passes.len(),
-            llvm_plugins.as_ptr().cast(),
+            llvm_plugins.as_c_char_ptr(),
             llvm_plugins.len(),
         )
     };
@@ -1042,7 +1043,7 @@ unsafe fn embed_bitcode(
             llvm::LLVMSetInitializer(llglobal, llconst);
 
             let section = bitcode_section_name(cgcx);
-            llvm::LLVMSetSection(llglobal, section.as_ptr().cast());
+            llvm::LLVMSetSection(llglobal, section.as_c_char_ptr());
             llvm::set_linkage(llglobal, llvm::Linkage::PrivateLinkage);
             llvm::LLVMSetGlobalConstant(llglobal, llvm::True);
 
@@ -1066,9 +1067,9 @@ unsafe fn embed_bitcode(
             // We need custom section flags, so emit module-level inline assembly.
             let section_flags = if cgcx.is_pe_coff { "n" } else { "e" };
             let asm = create_section_with_flags_asm(".llvmbc", section_flags, bitcode);
-            llvm::LLVMAppendModuleInlineAsm(llmod, asm.as_ptr().cast(), asm.len());
+            llvm::LLVMAppendModuleInlineAsm(llmod, asm.as_c_char_ptr(), asm.len());
             let asm = create_section_with_flags_asm(".llvmcmd", section_flags, cmdline.as_bytes());
-            llvm::LLVMAppendModuleInlineAsm(llmod, asm.as_ptr().cast(), asm.len());
+            llvm::LLVMAppendModuleInlineAsm(llmod, asm.as_c_char_ptr(), asm.len());
         }
     }
 }