--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lld/MachO/MarkLive.cpp	Tue Jun 08 06:07:14 2021 +0900
@@ -0,0 +1,189 @@
+//===- MarkLive.cpp -------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "MarkLive.h"
+#include "Config.h"
+#include "OutputSegment.h"
+#include "SymbolTable.h"
+#include "Symbols.h"
+#include "UnwindInfoSection.h"
+#include "mach-o/compact_unwind_encoding.h"
+#include "llvm/Support/TimeProfiler.h"
+
+namespace lld {
+namespace macho {
+
+using namespace llvm;
+using namespace llvm::MachO;
+
+// Set live bit on for each reachable chunk. Unmarked (unreachable)
+// InputSections will be ignored by Writer, so they will be excluded
+// from the final output.
+void markLive() {
+  TimeTraceScope timeScope("markLive");
+
+  // We build up a worklist of sections which have been marked as live. We only
+  // push into the worklist when we discover an unmarked section, and we mark
+  // as we push, so sections never appear twice in the list.
+  SmallVector<InputSection *, 256> worklist;
+
+  auto enqueue = [&](InputSection *s) {
+    if (s->live)
+      return;
+    s->live = true;
+    worklist.push_back(s);
+  };
+
+  auto addSym = [&](Symbol *s) {
+    s->used = true;
+    if (auto *d = dyn_cast<Defined>(s))
+      if (d->isec)
+        enqueue(d->isec);
+  };
+
+  // Add GC roots.
+  if (config->entry)
+    addSym(config->entry);
+  for (Symbol *sym : symtab->getSymbols()) {
+    if (auto *defined = dyn_cast<Defined>(sym)) {
+      // -exported_symbol(s_list)
+      if (!config->exportedSymbols.empty() &&
+          config->exportedSymbols.match(defined->getName())) {
+        // FIXME: Instead of doing this here, maybe the Driver code doing
+        // the matching should add them to explicitUndefineds? Then the
+        // explicitUndefineds code below would handle this automatically.
+        assert(!defined->privateExtern &&
+               "should have been rejected by driver");
+        addSym(defined);
+        continue;
+      }
+
+      // public symbols explicitly marked .no_dead_strip
+      if (defined->referencedDynamically || defined->noDeadStrip) {
+        addSym(defined);
+        continue;
+      }
+
+      // FIXME: When we implement these flags, make symbols from them GC roots:
+      // * -reexported_symbol(s_list)
+      // * -alias(-list)
+      // * -init
+
+      // In dylibs and bundles, all external functions are GC roots.
+      // FIXME: -export_dynamic should enable this for executables too.
+      if (config->outputType != MH_EXECUTE && !defined->privateExtern) {
+        addSym(defined);
+        continue;
+      }
+    }
+  }
+  // -u symbols
+  for (Symbol *sym : config->explicitUndefineds)
+    if (auto *defined = dyn_cast<Defined>(sym))
+      addSym(defined);
+  // local symbols explicitly marked .no_dead_strip
+  for (const InputFile *file : inputFiles)
+    if (auto *objFile = dyn_cast<ObjFile>(file))
+      for (Symbol *sym : objFile->symbols)
+        if (auto *defined = dyn_cast_or_null<Defined>(sym))
+          if (!defined->isExternal() && defined->noDeadStrip)
+            addSym(defined);
+  if (auto *stubBinder =
+          dyn_cast_or_null<DylibSymbol>(symtab->find("dyld_stub_binder")))
+    addSym(stubBinder);
+  for (InputSection *isec : inputSections) {
+    // Sections marked no_dead_strip
+    if (isec->flags & S_ATTR_NO_DEAD_STRIP) {
+      enqueue(isec);
+      continue;
+    }
+
+    // mod_init_funcs, mod_term_funcs sections
+    if (sectionType(isec->flags) == S_MOD_INIT_FUNC_POINTERS ||
+        sectionType(isec->flags) == S_MOD_TERM_FUNC_POINTERS) {
+      enqueue(isec);
+      continue;
+    }
+
+    // Dead strip runs before UnwindInfoSection handling so we need to keep
+    // __LD,__compact_unwind alive here.
+    // But that section contains absolute references to __TEXT,__text and
+    // keeps most code alive due to that. So we can't just enqueue() the
+    // section: We must skip the relocations for the functionAddress
+    // in each CompactUnwindEntry.
+    // See also scanEhFrameSection() in lld/ELF/MarkLive.cpp.
+    if (isec->segname == segment_names::ld &&
+        isec->name == section_names::compactUnwind) {
+      isec->live = true;
+      const int compactUnwindEntrySize =
+          target->wordSize == 8 ? sizeof(CompactUnwindEntry<uint64_t>)
+                                : sizeof(CompactUnwindEntry<uint32_t>);
+      for (const Reloc &r : isec->relocs) {
+        // This is the relocation for the address of the function itself.
+        // Ignore it, else these would keep everything alive.
+        if (r.offset % compactUnwindEntrySize == 0)
+          continue;
+
+        if (auto *s = r.referent.dyn_cast<Symbol *>())
+          addSym(s);
+        else {
+          auto *referentIsec = r.referent.get<InputSection *>();
+          assert(!referentIsec->isCoalescedWeak());
+          enqueue(referentIsec);
+        }
+      }
+      continue;
+    }
+  }
+
+  do {
+    // Mark things reachable from GC roots as live.
+    while (!worklist.empty()) {
+      InputSection *s = worklist.pop_back_val();
+      assert(s->live && "We mark as live when pushing onto the worklist!");
+
+      // Mark all symbols listed in the relocation table for this section.
+      for (const Reloc &r : s->relocs) {
+        if (auto *s = r.referent.dyn_cast<Symbol *>()) {
+          addSym(s);
+        } else {
+          auto *referentIsec = r.referent.get<InputSection *>();
+          assert(!referentIsec->isCoalescedWeak());
+          enqueue(referentIsec);
+        }
+      }
+    }
+
+    // S_ATTR_LIVE_SUPPORT sections are live if they point _to_ a live section.
+    // Process them in a second pass.
+    for (InputSection *isec : inputSections) {
+      // FIXME: Check if copying all S_ATTR_LIVE_SUPPORT sections into a
+      // separate vector and only walking that here is faster.
+      if (!(isec->flags & S_ATTR_LIVE_SUPPORT) || isec->live)
+        continue;
+
+      for (const Reloc &r : isec->relocs) {
+        bool referentLive;
+        if (auto *s = r.referent.dyn_cast<Symbol *>())
+          referentLive = s->isLive();
+        else
+          referentLive = r.referent.get<InputSection *>()->live;
+        if (referentLive)
+          enqueue(isec);
+      }
+    }
+
+    // S_ATTR_LIVE_SUPPORT could have marked additional sections live,
+    // which in turn could mark additional S_ATTR_LIVE_SUPPORT sections live.
+    // Iterate. In practice, the second iteration won't mark additional
+    // S_ATTR_LIVE_SUPPORT sections live.
+  } while (!worklist.empty());
+}
+
+} // namespace macho
+} // namespace lld