[lld-macho] Partial support for weak definitions

[int3]

Summary

This diff adds support for weak definitions, though it doesn't handle weak
symbols in dylibs quite correctly -- we need to emit binding opcodes for them
in the weak binding section rather than the lazy binding section.

What *is* covered in this diff:

1. Reading the weak flag from symbol table / export trie, and writing it to the export trie
2. Refining the symbol table's rules for choosing one symbol definition over another. Wrote a few dozen test cases to make sure we were matching ld64's behavior.

We can now link basic C++ programs.

[compnerd]

lld/MachO/ExportTrie.cpp

63

Can you please mark this explicit?

lld/MachO/ExportTrie.h

40

Are we sure we wont need any other flags? I wonder if it's better to just treat weakness as a flag. IIRC, there is a EXPORT_SYMBOL_FLAGS_REEXPORT and EXPORT_SYMBOL_FLAGS_KIND_THREAD_LOCAL that would be fairly good to account for.

lld/MachO/InputFiles.cpp

235

It's okay if you want to use braces, but please use them on both sides. However, I think that this is better written as:

if (sym.n_type & N_EXT)
  return symtab->addDefined(name, isec, value, sym.n_desc & N_WEAK_DEF);
return make<Defined>(name, isec, value, sym.n_desc & N_WEAK_DEF);

lld/MachO/SymbolTable.cpp

52

What do you think of doing an early return instead if the symbol was inserted?

Can you explain why currently it is not an error if the symbol is not inserted and not defined? Seems like a comment for that would be good.

[int3]

address comments

lld/MachO/ExportTrie.h

40

Yeah I wasn't super sure about how to organize this. My reason for making it a bool is so that the trie-decoding-specific logic can all live in ExportTrie.cpp. But having a whole bunch of boolean parameters in a callback isn't the prettiest either. But I figure we can switch it back later if necessary as we support more flags (or think of a different, cleaner API)

lld/MachO/InputFiles.cpp

235

oh yeah the braces were accidentally left over after some editing

lld/MachO/SymbolTable.cpp

52

not inserted and not defined => we will fall through to replaceSymbol below which will replace any Undefined/Lazy/Dylib symbols with the Defined one

[compnerd]

lld/MachO/ExportTrie.h

40

I'm pretty confident that we will need to add a few more flags at the very least. IMO the migration from uint64_t to bool here is really a step backwards.

lld/MachO/SymbolTable.cpp

52

I think that my confusion here is that the not inserted implies that it already exists, but because the cast to Defined failed, it cannot be a defined symbol, so you are replacing it with an undefined symbol or or something else? Do we know what is replacing the symbol? If it is not defined, then why is this function called addDefined?

[int3]

lld/MachO/ExportTrie.h

40

okay, I don't feel super strongly about this so I can revert

lld/MachO/SymbolTable.cpp

52

the cast to Defined failing means that the existing symbol isn't Defined, and so we're replacing it with a Defined symbol. I'm not sure why you think we may be replacing it with an undefined symbol, but note that replaceSymbol is changing the value and type of s via placement new (maybe you thought it was inserting s?)

[int3]

revert to flags

[smeenai]

lld/MachO/InputFiles.cpp

398

Super super nit: convention is to format the comments as /*isWeakDef=*/false

lld/MachO/Symbols.h

53

How would you feel about making the field private and adding an accessor which asserts it's only called on the right kind of symbol? (Ordinarily I would have suggested a virtual method with subclass overrides, but it looks like lld keeps Symbol free of virtual methods, and with an assert we wouldn't have any overhead in no-assert builds.)

77

Not that it holds any meaning for undefined symbols, but how come we're setting isWeakDef to true?

97

Nit: missing the comment for the boolean argument.

lld/test/MachO/weak-definition-direct-fetch.s

31

LLD will read archives of all formats fine, but technically we should pass --format=darwin to get a Darwin archive.

48

Was the order of -lweakfoo and -lfoo meant to be switched in this line?

65

I assume the intended behavior is that whichever comes first on the command line (the archive or the object) wins out. Is it worth testing that explicitly? (As in, by creating a different object file that's part of the archive, perhaps with the symbol in a different section.)

70

Huh, interesting.

lld/test/MachO/weak-definition-indirect-fetch.s

7

"some other symbol in the archive member being referenced" would be more precise.

14

Is it necessary to have the callq _foo?

lld/test/MachO/weak-definition-order.s

13

Do we need this test for archives as well?

lld/test/MachO/weak-definition-over-dysym.s

27

Doesn't this contradict the test in weak-definition-direct-fetch that I commented "Huh, interesting" on?

Is weak-definition-direct-fetch not testing all these cases already?

[int3]

address comments

lld/MachO/Symbols.h

53

I actually add virtual methods to Symbol in D83603, so I can do it here too

77

no reason really, Undefined symbols are just weak compared to everything else, so I figured why not :p but yeah not having redundant members will make more sense

lld/test/MachO/weak-definition-direct-fetch.s

48

oops yeah

65

I'm confused. Was your comment intended for this line? We're only testing archive vs dylib here...

But in any case, for object vs archive, the object always wins out. Lines 82-85 demonstrate that.

lld/test/MachO/weak-definition-indirect-fetch.s

14

nope, will remove

lld/test/MachO/weak-definition-order.s

13

from the other tests it's pretty clear that the weak flag has no impact on archive symbols, so I figured it wasn't really necessary to test them here...

lld/test/MachO/weak-definition-over-dysym.s

27

The difference is that this isn't a "direct fetch". Pulling in _bar causes _foo to be pulled in too and take priority over the dylib symbol.

[compnerd]

lld/MachO/SymbolTable.cpp

52

Ah, now I follow. I think it would be nice to have that as a comment.

[int3]

add comment

lld/MachO/Arch/X86_64.cpp

void X86_64::prepareSymbolRelocation(lld::macho::Symbol &sym,
                                      const InputSection *isec, const Reloc &r) {
   switch (r.type) {
   case X86_64_RELOC_GOT_LOAD:
     // TODO: implement mov -> lea relaxation for non-dynamic symbols
   case X86_64_RELOC_GOT:
     in.got->addEntry(sym);
     break;
   case X86_64_RELOC_BRANCH: {
+    // TODO: weak dysyms should go into the weak binding section instead
     if (auto *dysym = dyn_cast<DylibSymbol>(&sym))
       in.stubs->addEntry(*dysym);
     break;
   }
   case X86_64_RELOC_UNSIGNED: {
     if (auto *dysym = dyn_cast<DylibSymbol>(&sym)) {
       if (r.length != 3) {
         error("X86_64_RELOC_UNSIGNED referencing the dynamic symbol " +

lld/MachO/ExportTrie.h

private:
   void sortAndBuild(llvm::MutableArrayRef<const Symbol *> vec, TrieNode *node,
                     size_t lastPos, size_t pos);
 
   std::vector<const Symbol *> exported;
   std::vector<TrieNode *> nodes;
 };
 
 using TrieEntryCallback =
-    llvm::function_ref<void(const llvm::Twine & /*name*/, uint64_t /*flags*/)>;
+    llvm::function_ref<void(const llvm::Twine & /*name*/, bool /*isWeakDef*/)>;
 
 void parseTrie(const uint8_t *buf, size_t size, const TrieEntryCallback &);
 
 } // namespace macho
 } // namespace lld
 
 #endif

lld/MachO/ExportTrie.cpp

struct Edge {
   Edge(StringRef s, TrieNode *node) : substring(s), child(node) {}
 
   StringRef substring;
   struct TrieNode *child;
 };
 
 struct ExportInfo {
   uint64_t address;
+  uint8_t flags;
+  ExportInfo(const Symbol &sym)
+      : address(sym.getVA()),
+        flags(sym.isWeakDef ? EXPORT_SYMBOL_FLAGS_WEAK_DEFINITION : 0) {}
   // TODO: Add proper support for re-exports & stub-and-resolver flags.
 };
 
 } // namespace
 
 struct macho::TrieNode {
   std::vector<Edge> edges;
   Optional<ExportInfo> info;
   // Estimated offset from the start of the serialized trie to the current node.
   // This will converge to the true offset when updateOffset() is run to a
   // fixpoint.
   size_t offset = 0;
 
   // Returns whether the new estimated offset differs from the old one.
   bool updateOffset(size_t &nextOffset);
   void writeTo(uint8_t *buf) const;
 };
 
 bool TrieNode::updateOffset(size_t &nextOffset) {
   // Size of the whole node (including the terminalSize and the outgoing edges.)
   // In contrast, terminalSize only records the size of the other data in the
   // node.
   size_t nodeSize;
   if (info) {
-    uint64_t flags = 0;
     uint32_t terminalSize =
-        getULEB128Size(flags) + getULEB128Size(info->address);
+        getULEB128Size(info->flags) + getULEB128Size(info->address);
     // Overall node size so far is the uleb128 size of the length of the symbol
     // info + the symbol info itself.
     nodeSize = terminalSize + getULEB128Size(terminalSize);
   } else {
     nodeSize = 1; // Size of terminalSize (which has a value of 0)
   }
   // Compute size of all child edges.
   ++nodeSize; // Byte for number of children.
   for (Edge &edge : edges) {
     nodeSize += edge.substring.size() + 1             // String length.
                 + getULEB128Size(edge.child->offset); // Offset len.
   }
   // On input, 'nextOffset' is the new preferred location for this node.
   bool result = (offset != nextOffset);
   // Store new location in node object for use by parents.
   offset = nextOffset;
   nextOffset += nodeSize;
   return result;
 }
 
 void TrieNode::writeTo(uint8_t *buf) const {
   buf += offset;
   if (info) {
     // TrieNodes with Symbol info: size, flags address
-    uint64_t flags = 0; // TODO: emit proper flags
     uint32_t terminalSize =
-        getULEB128Size(flags) + getULEB128Size(info->address);
+        getULEB128Size(info->flags) + getULEB128Size(info->address);
     buf += encodeULEB128(terminalSize, buf);
-    buf += encodeULEB128(flags, buf);
+    buf += encodeULEB128(info->flags, buf);
     buf += encodeULEB128(info->address, buf);
   } else {
     // TrieNode with no Symbol info.
     *buf++ = 0; // terminalSize
   }
   // Add number of children. TODO: Handle case where we have more than 256.
   assert(edges.size() < 256);
   *buf++ = edges.size();
if (lastPos != pos && (isTerminal || prefixesDiverge)) {
     lastPos = pos;
   }
 
   sortAndBuild(vec.slice(0, i), node, lastPos, pos);
   sortAndBuild(vec.slice(j), node, lastPos, pos);
 
   if (isTerminal) {
     assert(j - i == 1); // no duplicate symbols
-    node->info = {pivotSymbol->getVA()};
+    node->info = ExportInfo(*pivotSymbol);
   } else {
     // This is the tail-call-optimized version of the following:
     // sortAndBuild(vec.slice(i, j - i), node, lastPos, pos + 1);
     vec = vec.slice(i, j - i);
     ++pos;
     goto tailcall;
   }
 }
void TrieParser::parse(const uint8_t *buf, const Twine &cumulativeString) {
 
   unsigned ulebSize;
   uint64_t terminalSize = decodeULEB128(buf, &ulebSize);
   buf += ulebSize;
   uint64_t flags = 0;
   size_t offset;
   if (terminalSize != 0) {
     flags = decodeULEB128(buf, &ulebSize);
-    callback(cumulativeString, flags);
+    callback(cumulativeString, flags & EXPORT_SYMBOL_FLAGS_WEAK_DEFINITION);
   }
   buf += terminalSize;
   uint8_t numEdges = *buf++;
   for (uint8_t i = 0; i < numEdges; ++i) {
     const char *cbuf = reinterpret_cast<const char *>(buf);
     StringRef substring = StringRef(cbuf, strnlen(cbuf, end - buf));
     buf += substring.size() + 1;
     offset = decodeULEB128(buf, &ulebSize);

lld/MachO/InputFiles.cpp

void InputFile::parseSymbols(ArrayRef<structs::nlist_64> nList,
   // resize(), not reserve(), because we are going to create N_ALT_ENTRY symbols
   // out-of-sequence.
   symbols.resize(nList.size());
   std::vector<size_t> altEntrySymIdxs;
 
   auto createDefined = [&](const structs::nlist_64 &sym, InputSection *isec,
                            uint32_t value) -> Symbol * {
     StringRef name = strtab + sym.n_strx;
-    if (sym.n_type & N_EXT)
+    if (sym.n_type & N_EXT) {
       // Global defined symbol
-      return symtab->addDefined(name, isec, value);
-    else
+      return symtab->addDefined(name, isec, value, sym.n_desc & N_WEAK_DEF);
+    } else
       // Local defined symbol
-      return make<Defined>(name, isec, value);
+      return make<Defined>(name, isec, value, sym.n_desc & N_WEAK_DEF);
   };
 
   for (size_t i = 0, n = nList.size(); i < n; ++i) {
     const structs::nlist_64 &sym = nList[i];
 
     // Undefined symbol
     if (!sym.n_sect) {
       StringRef name = strtab + sym.n_strx;
       symbols[i] = symtab->addUndefined(name);
if (const load_command *cmd = findCommand(hdr, LC_ID_DYLIB)) {
     error("dylib " + getName() + " missing LC_ID_DYLIB load command");
     return;
   }
 
   // Initialize symbols.
   if (const load_command *cmd = findCommand(hdr, LC_DYLD_INFO_ONLY)) {
     auto *c = reinterpret_cast<const dyld_info_command *>(cmd);
     parseTrie(buf + c->export_off, c->export_size,
-              [&](const Twine &name, uint64_t flags) {
-                symbols.push_back(symtab->addDylib(saver.save(name), umbrella));
+              [&](const Twine &name, bool isWeakDef) {
+                symbols.push_back(
+                    symtab->addDylib(saver.save(name), umbrella, isWeakDef));
               });
   } else {
     error("LC_DYLD_INFO_ONLY not found in " + getName());
     return;
   }
 
   if (hdr->flags & MH_NO_REEXPORTED_DYLIBS)
     return;

 DylibFile::DylibFile(std::shared_ptr<llvm::MachO::InterfaceFile> interface,
                      DylibFile *umbrella)
     : InputFile(DylibKind, MemoryBufferRef()) {
   if (umbrella == nullptr)
     umbrella = this;
 
   dylibName = saver.save(interface->getInstallName());
   // TODO(compnerd) filter out symbols based on the target platform
+  // TODO: handle weak defs
   for (const auto symbol : interface->symbols())
     if (symbol->getArchitectures().has(config->arch))
-      symbols.push_back(
-          symtab->addDylib(saver.save(symbol->getName()), umbrella));
+      symbols.push_back(symtab->addDylib(saver.save(symbol->getName()),
+                                         umbrella, /*isWeakDef*/ false));
   // TODO(compnerd) properly represent the hierarchy of the documents as it is
   // in theory possible to have re-exported dylibs from re-exported dylibs which
   // should be parent'ed to the child.
   for (auto document : interface->documents())
     reexported.push_back(make<DylibFile>(document, umbrella));
 }
 
 ArchiveFile::ArchiveFile(std::unique_ptr<llvm::object::Archive> &&f)

lld/MachO/SymbolTable.h

 
 class ArchiveFile;
 class DylibFile;
 class InputSection;
 class Symbol;
 
 class SymbolTable {
 public:
-  Symbol *addDefined(StringRef name, InputSection *isec, uint32_t value);
+  Symbol *addDefined(StringRef name, InputSection *isec, uint32_t value,
+                     bool isWeakDef);
 
   Symbol *addUndefined(StringRef name);
 
-  Symbol *addDylib(StringRef name, DylibFile *file);
+  Symbol *addDylib(StringRef name, DylibFile *file, bool isWeakDef);
 
   Symbol *addLazy(StringRef name, ArchiveFile *file,
                   const llvm::object::Archive::Symbol &sym);
 
   ArrayRef<Symbol *> getSymbols() const { return symVector; }
   Symbol *find(StringRef name);
 
 private:

lld/MachO/SymbolTable.cpp

std::pair<Symbol *, bool> SymbolTable::insert(StringRef name) {
 
   // Name is a new symbol.
   Symbol *sym = reinterpret_cast<Symbol *>(make<SymbolUnion>());
   symVector.push_back(sym);
   return {sym, true};
 }
 
 Symbol *SymbolTable::addDefined(StringRef name, InputSection *isec,
-                                uint32_t value) {
+                                uint32_t value, bool isWeakDef) {
   Symbol *s;
   bool wasInserted;
   std::tie(s, wasInserted) = insert(name);
 
-  if (!wasInserted && isa<Defined>(s))
+  if (!wasInserted) {
+    if (auto *defined = dyn_cast<Defined>(s)) {
+      if (isWeakDef)
+        return s;
+      if (!defined->isWeakDef)
         error("duplicate symbol: " + name);
+    }
+  }
 
-  replaceSymbol<Defined>(s, name, isec, value);
+  replaceSymbol<Defined>(s, name, isec, value, isWeakDef);
   return s;
 }
 
 Symbol *SymbolTable::addUndefined(StringRef name) {
   Symbol *s;
   bool wasInserted;
   std::tie(s, wasInserted) = insert(name);
 
   if (wasInserted)
     replaceSymbol<Undefined>(s, name);
   else if (LazySymbol *lazy = dyn_cast<LazySymbol>(s))
     lazy->fetchArchiveMember();
   return s;
 }
 
-Symbol *SymbolTable::addDylib(StringRef name, DylibFile *file) {
+Symbol *SymbolTable::addDylib(StringRef name, DylibFile *file, bool isWeakDef) {
   Symbol *s;
   bool wasInserted;
   std::tie(s, wasInserted) = insert(name);
 
-  if (wasInserted || isa<Undefined>(s))
-    replaceSymbol<DylibSymbol>(s, file, name);
+  if (wasInserted || isa<Undefined>(s) ||
+      (isa<DylibSymbol>(s) && !isWeakDef && s->isWeakDef))
+    replaceSymbol<DylibSymbol>(s, file, name, isWeakDef);
+
   return s;
 }
 
 Symbol *SymbolTable::addLazy(StringRef name, ArchiveFile *file,
                              const llvm::object::Archive::Symbol &sym) {
   Symbol *s;
   bool wasInserted;
   std::tie(s, wasInserted) = insert(name);
 
   if (wasInserted)
     replaceSymbol<LazySymbol>(s, file, sym);
-  else if (isa<Undefined>(s))
+  else if (isa<Undefined>(s) || (isa<DylibSymbol>(s) && s->isWeakDef))
     file->fetch(sym);
   return s;
 }
 
 SymbolTable *macho::symtab;

lld/MachO/Symbols.h

public:
   StringRef getName() const { return {name.data, name.size}; }
 
   uint64_t getVA() const;
 
   uint64_t getFileOffset() const;
 
   uint32_t gotIndex = UINT32_MAX;
 
+  // This bool is only meaningful for Defineds and DylibSymbols.
+  const bool isWeakDef;
+
 protected:
-  Symbol(Kind k, StringRefZ name) : symbolKind(k), name(name) {}
+  Symbol(Kind k, StringRefZ name, bool isWeakDef)
+      : isWeakDef(isWeakDef), symbolKind(k), name(name) {}
 
   Kind symbolKind;
   StringRefZ name;
 };
 
 class Defined : public Symbol {
 public:
-  Defined(StringRefZ name, InputSection *isec, uint32_t value)
-      : Symbol(DefinedKind, name), isec(isec), value(value) {}
+  Defined(StringRefZ name, InputSection *isec, uint32_t value, bool isWeakDef)
+      : Symbol(DefinedKind, name, isWeakDef), isec(isec), value(value) {}
 
   InputSection *isec;
   uint32_t value;
 
   static bool classof(const Symbol *s) { return s->kind() == DefinedKind; }
 };
 
 class Undefined : public Symbol {
 public:
-  Undefined(StringRefZ name) : Symbol(UndefinedKind, name) {}
+  Undefined(StringRefZ name)
+      : Symbol(UndefinedKind, name, /*isWeakDef*/ true) {}
 
   static bool classof(const Symbol *s) { return s->kind() == UndefinedKind; }
 };
 
 class DylibSymbol : public Symbol {
 public:
-  DylibSymbol(DylibFile *file, StringRefZ name)
-      : Symbol(DylibKind, name), file(file) {}
+  DylibSymbol(DylibFile *file, StringRefZ name, bool isWeakDef)
+      : Symbol(DylibKind, name, isWeakDef), file(file) {}
 
   static bool classof(const Symbol *s) { return s->kind() == DylibKind; }
 
   DylibFile *file;
   uint32_t stubsIndex = UINT32_MAX;
   uint32_t lazyBindOffset = UINT32_MAX;
 };
 
 class LazySymbol : public Symbol {
 public:
   LazySymbol(ArchiveFile *file, const llvm::object::Archive::Symbol &sym)
-      : Symbol(LazyKind, sym.getName()), file(file), sym(sym) {}
+      : Symbol(LazyKind, sym.getName(), false), file(file), sym(sym) {}
 
   static bool classof(const Symbol *s) { return s->kind() == LazyKind; }
 
   void fetchArchiveMember();
 
 private:
   ArchiveFile *file;
   const llvm::object::Archive::Symbol sym;

lld/MachO/SyntheticSections.cpp

void StubHelperSection::setup() {
   if (stubBinder == nullptr) {
     error("symbol dyld_stub_binder not found (normally in libSystem.dylib). "
           "Needed to perform lazy binding.");
     return;
   }
   in.got->addEntry(*stubBinder);
 
   inputSections.push_back(in.imageLoaderCache);
-  symtab->addDefined("__dyld_private", in.imageLoaderCache, 0);
+  symtab->addDefined("__dyld_private", in.imageLoaderCache, 0,
+                     /*isWeakDef*/ false);
 }
 
 ImageLoaderCacheSection::ImageLoaderCacheSection() {
   segname = segment_names::data;
   name = "__data";
   uint8_t *arr = bAlloc.Allocate<uint8_t>(WordSize);
   memset(arr, 0, WordSize);
   data = {arr, WordSize};

lld/test/MachO/weak-definition-direct-fetch.s

+# REQUIRES: x86
+# RUN: mkdir -p %t
+
+## This test exercises the various possible combinations of weak and non-weak
+## symbols that get referenced directly by a relocation in an object file.
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
+# RUN: echo ".globl _foo; .section __TEXT,nonweak; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/foo.o
+# RUN: echo ".globl _foo; .weak_definition _foo; .section __TEXT,weak; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/weakfoo.o
+
+# RUN: lld -flavor darwinnew -dylib -install_name \
+# RUN:   @executable_path/libfoo.dylib %t/foo.o -o %t/libfoo.dylib
+# RUN: lld -flavor darwinnew -dylib -install_name \
+# RUN:   @executable_path/libweakfoo.dylib %t/weakfoo.o -o %t/libweakfoo.dylib
+
+# RUN: llvm-objdump --macho --exports-trie %t/libweakfoo.dylib | FileCheck %s --check-prefix WEAK-DYLIB-CHECK
+# WEAK-DYLIB-CHECK: _foo [weak_def]
+
+## Make sure we are using the export trie and not the symbol table when linking
+## against these dylibs.
+# RUN: llvm-strip %t/libfoo.dylib
+# RUN: llvm-strip %t/libweakfoo.dylib
+# RUN: llvm-nm %t/libfoo.dylib 2>&1 | FileCheck %s --check-prefix=NOSYM
+# RUN: llvm-nm %t/libweakfoo.dylib 2>&1 | FileCheck %s --check-prefix=NOSYM
+# NOSYM: no symbols
+
+# RUN: rm -f %t/foo.a
+# RUN: llvm-ar rcs %t/foo.a %t/foo.o
+# RUN: rm -f %t/weakfoo.a
+# RUN: llvm-ar rcs %t/weakfoo.a %t/weakfoo.o
+
+## End of input file setup. The following lines check which symbol "wins" when
+## there are multiple definitions.
+
+# PREFER-NONWEAK-DYLIB:  __DATA __la_symbol_ptr 0x{{[0-9a-f]+}} libfoo _foo
+# PREFER-WEAK-OBJECT:    O __TEXT,weak _foo
+# PREFER-NONWEAK-OBJECT: O __TEXT,nonweak _foo
+
+## First, we test the cases where the symbols are of the same type (both from a
+## dylib, or both from an archive, etc.)
+##
+## For dylibs and object files, the non-weak symbol always wins. But the weak
+## flag has no effect when we are dealing with two archive symbols.
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-nonweak-dylibs -Z -L%t -lweakfoo -lfoo %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-nonweak-dylibs | FileCheck %s --check-prefix=PREFER-NONWEAK-DYLIB
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-weak-dylibs -Z -L%t -lweakfoo -lfoo %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/nonweak-weak-dylibs | FileCheck %s --check-prefix=PREFER-NONWEAK-DYLIB
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-nonweak-objs -Z -L%t %t/weakfoo.o %t/foo.o %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-nonweak-objs | FileCheck %s --check-prefix=PREFER-NONWEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-weak-objs -Z -L%t %t/foo.o %t/weakfoo.o %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/nonweak-weak-objs | FileCheck %s --check-prefix=PREFER-NONWEAK-OBJECT
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-nonweak-archives -Z -L%t %t/weakfoo.a %t/foo.a %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-nonweak-archives | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-weak-archives -Z -L%t %t/foo.a %t/weakfoo.a %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/nonweak-weak-archives | FileCheck %s --check-prefix=PREFER-NONWEAK-OBJECT
+
+## The remaining lines test symbol pairs of different types.
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-dylib-weak-ar -Z -L%t -lweakfoo %t/weakfoo.a %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-dylib-weak-ar | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-ar-weak-dylib -Z -L%t %t/weakfoo.a -lweakfoo %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-ar-weak-dylib | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-ar-nonweak-dylib -Z -L%t %t/weakfoo.a -lfoo %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-ar-nonweak-dylib | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-dylib-weak-ar -Z -L%t -lfoo %t/weakfoo.a %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/nonweak-dylib-weak-ar | FileCheck %s --check-prefix=PREFER-NONWEAK-DYLIB
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-dylib-weak-obj -Z -L%t -lweakfoo %t/weakfoo.o %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-dylib-weak-obj | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-obj-weak-dylib -Z -L%t %t/weakfoo.o -lweakfoo %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-obj-weak-dylib | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-obj-nonweak-dylib -Z -L%t %t/weakfoo.o -lfoo %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-obj-nonweak-dylib | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-dylib-weak-obj -Z -L%t -lfoo %t/weakfoo.o %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/nonweak-dylib-weak-obj | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-obj-nonweak-ar -Z -L%t %t/weakfoo.o %t/foo.a %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-obj-nonweak-ar | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-ar-weak-obj -Z -L%t %t/foo.a %t/weakfoo.o %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/nonweak-ar-weak-obj | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+
+.globl _main
+_main:
+  callq _foo
+  ret

lld/test/MachO/weak-definition-indirect-fetch.s

+# REQUIRES: x86
+# RUN: mkdir -p %t
+
+## This tests examines the effect of .weak_definition on symbols in an archive
+## that are not referenced directly, but which are still loaded due to some
+## other symbol in the archive being referenced.
+##
+## In this particular test, _foo isn't referenced directly, but both archives
+## will be fetched when linking against the main test file due to its references
+## to _bar and _baz.
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
+# RUN: echo ".globl _foo, _bar; .section __TEXT,nonweak; _bar: callq _foo; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/foo.o
+# RUN: echo ".globl _foo, _baz; .weak_definition _foo; .section __TEXT,weak; _baz: callq _foo; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/weakfoo.o
+
+# RUN: rm -f %t/foo.a
+# RUN: llvm-ar rcs %t/foo.a %t/foo.o
+# RUN: rm -f %t/weakfoo.a
+# RUN: llvm-ar rcs %t/weakfoo.a %t/weakfoo.o
+
+# PREFER-NONWEAK-OBJECT: O __TEXT,nonweak _foo
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-nonweak-archives -Z -L%t %t/weakfoo.a %t/foo.a %t/test.o
+# RUN: llvm-objdump --syms %t/weak-nonweak-archives | FileCheck %s --check-prefix=PREFER-NONWEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-weak-archives -Z -L%t %t/foo.a %t/weakfoo.a %t/test.o
+# RUN: llvm-objdump --syms %t/nonweak-weak-archives | FileCheck %s --check-prefix=PREFER-NONWEAK-OBJECT
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-nonweak-objs -Z -L%t %t/weakfoo.o %t/foo.o %t/test.o
+# RUN: llvm-objdump --syms %t/weak-nonweak-objs | FileCheck %s --check-prefix=PREFER-NONWEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-weak-objs -Z -L%t %t/foo.o %t/weakfoo.o %t/test.o
+# RUN: llvm-objdump --syms %t/nonweak-weak-objs | FileCheck %s --check-prefix=PREFER-NONWEAK-OBJECT
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-obj-nonweak-ar -Z -L%t %t/weakfoo.o %t/foo.a %t/test.o
+# RUN: llvm-objdump --syms %t/weak-obj-nonweak-ar | FileCheck %s --check-prefix=PREFER-NONWEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-ar-weak-obj -Z -L%t %t/foo.a %t/weakfoo.o %t/test.o
+# RUN: llvm-objdump --syms %t/nonweak-ar-weak-obj | FileCheck %s --check-prefix=PREFER-NONWEAK-OBJECT
+
+.globl _main
+_main:
+  callq _bar
+  callq _baz
+  ret

lld/test/MachO/weak-definition-order.s

+# REQUIRES: x86
+# RUN: mkdir -p %t
+
+## This test demonstrates that when we have two weak symbols of the same type,
+## we pick the one whose containing file appears earlier in the command-line
+## invocation.
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
+# RUN: echo ".globl _foo; .weak_definition _foo; .section __TEXT,weak1; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/weak1.o
+# RUN: echo ".globl _foo; .weak_definition _foo; .section __TEXT,weak2; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/weak2.o
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/obj12 -Z -L%t %t/weak1.o %t/weak2.o %t/test.o
+# RUN: llvm-objdump --syms %t/obj12 | FileCheck %s --check-prefix=WEAK1
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/obj21 -Z -L%t %t/weak2.o %t/weak1.o %t/test.o
+# RUN: llvm-objdump --syms %t/obj21 | FileCheck %s --check-prefix=WEAK2
+
+# WEAK1: O __TEXT,weak1 _foo
+# WEAK2: O __TEXT,weak2 _foo
+
+# RUN: lld -flavor darwinnew -dylib -install_name \
+# RUN:   @executable_path/libweak1.dylib %t/weak1.o -o %t/libweak1.dylib
+# RUN: lld -flavor darwinnew -dylib -install_name \
+# RUN:   @executable_path/libweak2.dylib %t/weak2.o -o %t/libweak2.dylib
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/dylib12 -Z -L%t -lweak1 -lweak2 %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind %t/dylib12 | FileCheck %s --check-prefix=DYLIB1
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/dylib21 -Z -L%t -lweak2 -lweak1 %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind %t/dylib21 | FileCheck %s --check-prefix=DYLIB2
+## TODO: these should really be in the weak binding section, not the lazy binding section
+# DYLIB1: __DATA   __la_symbol_ptr    0x{{[0-9a-f]*}} libweak1         _foo
+# DYLIB2: __DATA   __la_symbol_ptr    0x{{[0-9a-f]*}} libweak2         _foo
+
+.globl _main
+_main:
+  callq _foo
+  ret

lld/test/MachO/weak-definition-over-dysym.s

+# REQUIRES: x86
+# RUN: mkdir -p %t
+
+## This test demonstrates that when an archive file is fetched, its symbols
+## always override any conflicting dylib symbols, regardless of any weak
+## definition flags.
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
+# RUN: echo ".globl _foo; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/libfoo.o
+# RUN: lld -flavor darwinnew -dylib -install_name \
+# RUN:   @executable_path/libfoo.dylib %t/libfoo.o -o %t/libfoo.dylib
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
+# RUN: echo ".globl _foo, _bar; .section __TEXT,nonweak; _bar: callq _foo; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/foo.o
+# RUN: echo ".globl _foo, _bar; .weak_definition _foo; .section __TEXT,weak; _bar: callq _foo; _foo:" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/weakfoo.o
+
+# RUN: rm -f %t/foo.a
+# RUN: llvm-ar rcs %t/foo.a %t/foo.o
+# RUN: rm -f %t/weakfoo.a
+# RUN: llvm-ar rcs %t/weakfoo.a %t/weakfoo.o
+
+# PREFER-WEAK-OBJECT: O __TEXT,weak _foo
+# PREFER-NONWEAK-OBJECT: O __TEXT,nonweak _foo
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-dylib-weak-ar -Z -L%t -lfoo %t/weakfoo.a %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/nonweak-dylib-weak-ar | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-ar-nonweak-dylib -Z -L%t %t/weakfoo.a -lfoo %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-ar-nonweak-dylib | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/weak-obj-nonweak-dylib -Z -L%t %t/weakfoo.o -lfoo %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/weak-obj-nonweak-dylib | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+# RUN: lld -flavor darwinnew -L%S/Inputs/MacOSX.sdk/usr/lib -lSystem -o %t/nonweak-dylib-weak-obj -Z -L%t -lfoo %t/weakfoo.o %t/test.o
+# RUN: llvm-objdump --macho --lazy-bind --syms %t/nonweak-dylib-weak-obj | FileCheck %s --check-prefix=PREFER-WEAK-OBJECT
+
+.globl _main
+_main:
+  callq _foo
+  callq _bar
+  ret