[Mach-O] Deduplicate comdat sections

rui314 · May 21, 2022 · 0b6fa20 · 0b6fa20
1 parent e293d56
commit 0b6fa20
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Showing 2 changed files with 23 additions and 0 deletions.
diff --git a/macho/dead-strip.cc b/macho/dead-strip.cc
@@ -61,6 +61,10 @@ static bool refers_live_subsection(Subsection<E> &subsec) {
 
 template <typename E>
 static void mark(Context<E> &ctx, const std::vector<Subsection<E> *> &rootset) {
+  for (ObjectFile<E> *file : ctx.objs)
+    for (std::unique_ptr<Subsection<E>> &subsec : file->subsections)
+      subsec->is_alive = false;
+
   for (Subsection<E> *subsec : rootset)
     visit(ctx, *subsec);
 

diff --git a/macho/main.cc b/macho/main.cc
@@ -92,6 +92,23 @@ static void create_internal_file(Context<E> &ctx) {
   add("___dso_handle");
 }
 
+// Remove unreferenced subsections to eliminate code and data
+// referenced by duplicated weakdef symbols.
+template <typename E>
+static void remove_unreferenced_subsections(Context<E> &ctx) {
+  for (ObjectFile<E> *file : ctx.objs)
+    for (Symbol<E> *sym : file->syms)
+      if (sym->file == file && sym->subsec)
+        sym->subsec->is_alive = true;
+
+  for (ObjectFile<E> *file : ctx.objs) {
+    std::erase_if(file->subsections,
+                  [](const std::unique_ptr<Subsection<E>> &subsec) {
+      return !subsec->is_alive;
+    });
+  }
+}
+
 template <typename E>
 static bool compare_segments(const std::unique_ptr<OutputSegment<E>> &a,
                              const std::unique_ptr<OutputSegment<E>> &b) {
@@ -535,6 +552,8 @@ static int do_main(int argc, char **argv) {
   std::erase_if(ctx.objs, [](ObjectFile<E> *file) { return !file->is_alive; });
   std::erase_if(ctx.dylibs, [](DylibFile<E> *file) { return !file->is_alive; });
 
+  remove_unreferenced_subsections(ctx);
+
   if (ctx.arg.trace) {
     for (ObjectFile<E> *file : ctx.objs)
       SyncOut(ctx) << *file;