Rollup merge of rust-lang#131962 - Zalathar:llvm-set-section, r=Swatinem,workingjubilee

Make `llvm::set_section` take a `&CStr`

There's no reason to convert the section name to an intermediate `String`, when the LLVM-C API wants a C string anyway.

Follow-up to rust-lang#131876.

Author: matthiaskrgr

compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

@@ -1,3 +1,5 @@
+use std::ffi::CStr;
+
 use itertools::Itertools as _;
 use rustc_codegen_ssa::traits::{BaseTypeCodegenMethods, ConstCodegenMethods};
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
@@ -305,7 +307,7 @@ fn generate_coverage_map<'ll>(
 /// specific, well-known section and name.
 fn save_function_record(
     cx: &CodegenCx<'_, '_>,
-    covfun_section_name: &str,
+    covfun_section_name: &CStr,
     mangled_function_name: &str,
     source_hash: u64,
     filenames_ref: u64,

compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs

@@ -1,5 +1,5 @@
 use std::cell::RefCell;
-use std::ffi::CString;
+use std::ffi::{CStr, CString};
 
 use libc::c_uint;
 use rustc_codegen_ssa::traits::{
@@ -292,10 +292,10 @@ pub(crate) fn save_cov_data_to_mod<'ll, 'tcx>(
     .unwrap();
     debug!("covmap var name: {:?}", covmap_var_name);
 
-    let covmap_section_name = llvm::build_string(|s| unsafe {
+    let covmap_section_name = CString::new(llvm::build_byte_buffer(|s| unsafe {
         llvm::LLVMRustCoverageWriteMapSectionNameToString(cx.llmod, s);
-    })
-    .expect("Rust Coverage section name failed UTF-8 conversion");
+    }))
+    .expect("covmap section name should not contain NUL");
     debug!("covmap section name: {:?}", covmap_section_name);
 
     let llglobal = llvm::add_global(cx.llmod, cx.val_ty(cov_data_val), &covmap_var_name);
@@ -310,7 +310,7 @@ pub(crate) fn save_cov_data_to_mod<'ll, 'tcx>(
 
 pub(crate) fn save_func_record_to_mod<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
-    covfun_section_name: &str,
+    covfun_section_name: &CStr,
     func_name_hash: u64,
     func_record_val: &'ll llvm::Value,
     is_used: bool,
@@ -354,9 +354,9 @@ pub(crate) fn save_func_record_to_mod<'ll, 'tcx>(
 /// - `__llvm_covfun` on Linux
 /// - `__LLVM_COV,__llvm_covfun` on macOS (includes `__LLVM_COV,` segment prefix)
 /// - `.lcovfun$M` on Windows (includes `$M` sorting suffix)
-pub(crate) fn covfun_section_name(cx: &CodegenCx<'_, '_>) -> String {
-    llvm::build_string(|s| unsafe {
+pub(crate) fn covfun_section_name(cx: &CodegenCx<'_, '_>) -> CString {
+    CString::new(llvm::build_byte_buffer(|s| unsafe {
         llvm::LLVMRustCoverageWriteFuncSectionNameToString(cx.llmod, s);
-    })
-    .expect("Rust Coverage function record section name failed UTF-8 conversion")
+    }))
+    .expect("covfun section name should not contain NUL")
 }

compiler/rustc_codegen_llvm/src/llvm/mod.rs

@@ -210,10 +210,9 @@ impl MemoryEffects {
     }
 }
 
-pub fn set_section(llglobal: &Value, section_name: &str) {
-    let section_name_cstr = CString::new(section_name).expect("unexpected CString error");
+pub fn set_section(llglobal: &Value, section_name: &CStr) {
     unsafe {
-        LLVMSetSection(llglobal, section_name_cstr.as_ptr());
+        LLVMSetSection(llglobal, section_name.as_ptr());
     }
 }