set subsections_via_symbols for ld64 helper sections

Author: usamoi

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -2001,7 +2001,7 @@ fn add_linked_symbol_object(
         return;
     }
 
-    let Some(mut file) = super::metadata::create_object_file(sess) else {
+    let Some(mut file) = super::metadata::create_object_file(sess, true) else {
         return;
     };
 

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -200,7 +200,10 @@ pub(super) fn get_metadata_xcoff<'a>(path: &Path, data: &'a [u8]) -> Result<&'a
     }
 }
 
-pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static>> {
+pub(crate) fn create_object_file(
+    sess: &Session,
+    set_subsections_via_symbols: bool,
+) -> Option<write::Object<'static>> {
     let endianness = match sess.target.options.endian {
         Endian::Little => Endianness::Little,
         Endian::Big => Endianness::Big,
@@ -221,6 +224,11 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
 
         file.set_macho_build_version(macho_object_build_version_for_target(sess))
     }
+    if binary_format == BinaryFormat::MachO {
+        if set_subsections_via_symbols {
+            file.set_subsections_via_symbols();
+        }
+    }
     if binary_format == BinaryFormat::Coff {
         // Disable the default mangler to avoid mangling the special "@feat.00" symbol name.
         let original_mangling = file.mangling();
@@ -455,7 +463,7 @@ pub(crate) fn create_wrapper_file(
     section_name: String,
     data: &[u8],
 ) -> (Vec<u8>, MetadataPosition) {
-    let Some(mut file) = create_object_file(sess) else {
+    let Some(mut file) = create_object_file(sess, false) else {
         if sess.target.is_like_wasm {
             return (
                 create_metadata_file_for_wasm(sess, data, &section_name),
@@ -543,7 +551,7 @@ pub fn create_compressed_metadata_file(
     packed_metadata.write_all(&(metadata.stub_or_full().len() as u64).to_le_bytes()).unwrap();
     packed_metadata.extend(metadata.stub_or_full());
 
-    let Some(mut file) = create_object_file(sess) else {
+    let Some(mut file) = create_object_file(sess, false) else {
         if sess.target.is_like_wasm {
             return create_metadata_file_for_wasm(sess, &packed_metadata, ".rustc");
         }

tests/ui/linking/executable-no-mangle-strip.rs

@@ -0,0 +1,22 @@
+//@ build-pass
+
+// Regression test for <https://github.com/rust-lang/rust/issues/139744>.
+// Functions in the binary marked with no_mangle should be GC-ed if they
+// are not indirectly referenced by main.
+
+unsafe extern "C" {
+    unsafe static THIS_SYMBOL_SHOULD_BE_UNDEFINED: usize;
+}
+
+#[unsafe(no_mangle)]
+pub unsafe fn used() {
+    println!("THIS_SYMBOL_SHOULD_BE_UNDEFINED = {}", unsafe { THIS_SYMBOL_SHOULD_BE_UNDEFINED });
+}
+
+pub fn marker() -> usize {
+    0
+}
+
+fn main() {
+    assert_eq!(marker(), 0_usize);
+}