[lld-macho] Handle TAPI and regular re-exports uniformly

[int3]

Summary

The re-exports list in a TAPI document can either refer to other inlined
TAPI documents, or to on-disk files (which may themselves be TBD or
regular files.) Similarly, the re-exports of a regular dylib can refer
to a TBD file.

[int3]

lld/test/MachO/Inputs/iPhoneSimulator.sdk/usr/lib/libSystem.tbd

24

is not re-exported*

[int3]

update

[smeenai]

lld/MachO/Driver.cpp

133

IIUC, the previous version would prefer the tbd to the dylib, and resolveDylibPath will prefer the dylib to the TBD.

IIRC, if ld64 finds both a TBD and a dylib for the same file, it verifies the TBD against the dylib and falls back to the dylib in case of a mismatch. I don't think we need to implement that (and I don't think LLVM's version of TextAPI has the equivalence checking logic yet anyway), so perhaps always preferring the dylib in that case (as you're doing now) is reasonable.

182

This matches ld64's behavior as far as I can tell, so it looks good, but can you add a test? Both for this and for the standard search paths only being searched for under the syslibroots?

(This and the tests should also probably be their own diff.)

387–389

Can we get a test for this fix as well? (It should also probably be its own diff.)

lld/MachO/InputFiles.cpp

375

If I'm understanding correctly, this will only be able to find any inline documents we've seen in our input files thus far. Does this match ld64, or is it able to find inline documents from later files?

448–449

Nit: we're inconsistent about reexport vs reExport

lld/test/MachO/Inputs/MacOSX.sdk/usr/lib/libc++abi.tbd

5

Should this be libc++abi?

lld/test/MachO/reexport-stub.s

16

I thought that for sub-libraries, the bind information reflected the actual sub-library the symbol was coming from, and that seems to be the case in a basic test I did with ld64. Can you confirm how this is supposed to behave?

(IIRC there's options to re-export specific symbols, and those bind to the re-exporting library.)

[int3]

address some comments

lld/MachO/Driver.cpp

133

yeah, I did inadvertently change things here. From a quick glance at the code, I think your description of ld64's behavior is correct. ld64 can also take an environment variable that makes it always prefer the TAPI file. Do you know if having both the TAPI and the dylib has a real use case? Given the amount of logic ld64 has devoted to it, I guess there might be, but it seems odd. Maybe I could just raise an error for now if both are present?

182

yeah, sneaking this in here was sloppy, my bad :p

D85992: [lld-macho] Fall back to raw path if we don't find anything under syslibroot

387–389

whoops, I did not mean to leave this change in at all. It isn't a fix, it's wrong :p

lld/MachO/InputFiles.cpp

375

ld64 is indeed able to find documents from later files. It seems like pretty bizarre behavior to me, though -- what would be the use case? (In my initial implementation, I actually tried to limit re-exports in tbds to reference just those in the same file because I thought that made the most sense, but it was more awkward to implement that...)

lld/test/MachO/reexport-stub.s

16

Swapping ld64 for lld in this particular test gives the same result. (sub-library.s tests something similar, and ld64 binds to the parent library there too.) Can you share the test you did that showed a binding to the sub-library?

[smeenai]

lld/MachO/Driver.cpp

133

The Xcode 12 betas have both dylibs and TBDs present (for at least some of the SDKs), so erroring out in that case wouldn't be ideal. (I don't think the final Xcode releases every have dylibs.) I think it's fine to just use the dylib if you have both, and perhaps add a TODO to consider adding verification like ld64 has.

lld/MachO/InputFiles.cpp

375

Yeah, I'd also find it weird to reference sub-documents from other files, and I don't know if it's actually used in the SDKs.

lld/test/MachO/reexport-stub.s

16

I'm using ld64 530 from Xcode 11.3.1. If I try to run this test as-is (albeit with clang instead of llvm-mc), when I try to link test, I get an error:

ld: malformed mach-o, symbol table not in __LINKEDIT file './libreexporter.dylib'

I can just add a dummy symbol to work around that, and then

$ cat reexporter.s
.globl foo
foo:
	ret

$ cat test.s
.globl _main
_main:
	ret
.data
	.quad	___gxx_personality_v0

$ clang -c reexporter.s test.s
$ ld -dylib -lc++ -sub_library libc++ reexporter.o -o libreexporter.dylib
$ ld -o test -lSystem -L. -lreexporter test.o
$ objdump --bind test
Bind table:
segment  section            address    type       addend dylib            symbol
__DATA   __data             0x100001000 pointer         0 libc++           ___gxx_personality_v0

[int3]

lld/test/MachO/reexport-stub.s

16

hm, I must have messed up my first attempt, because I was able to see the binding to libc++ on my second try. But I figured out why sub-library.s doesn't repro the issue: bindings only get routed directly to re-exports if those re-exports have "public install names", i.e. if they live under /usr/lib/ or if they are a top-level framework under /System/Library/Frameworks/. I couldn't find any code comments explaining why, but I'm guessing it's an optimization -- I suppose the libraries with "public install names" form a stable ABI, and the only reason they get re-exported by other libraries is to provide some convenience to the user (who doesn't need to pass in half a dozen linker flags). Avoiding unnecessary re-export processing at runtime is probably a performance win.

Addressing this seems somewhat orthogonal to this diff, so a TODO comment should suffice for now?

[smeenai]

lld/test/MachO/reexport-stub.s

16

Ah, interesting. And yup, a TODO sounds good.

[int3]

add TODOs

lld/MachO/InputFiles.cpp

375

For a quick sanity check, I got lld to load all the non-Swift TBDs under the iPhone simulator's /usr/lib folder, and it worked fine. I did it twice, the second time with all the command-line -l arguments in reverse, and that worked too. So it seems like we don't have any cross-file references to inline documents.

[int3]

lld/test/MachO/reexport-stub.s

16

I've added the TODO to the DylibFile ctor.

[int3]

lld/MachO/Driver.cpp

387–389

my bad, a fix for this is actually necessary. Initial attempt was wrong though x:

real fix here: D86180

[int3]

rebase

[int3]

lld/test/MachO/reexport-stub.s

16

The manpage entry for -no_implicit_dylibs confirms my guess:

-no_implicit_dylibs
            When creating a two-level namespace final linked image, normally the
            linker will hoist up public dylibs that are implicitly linked to make the
            two-level namespace encoding more efficient for dyld.  For example, Cocoa
            re-exports AppKit and AppKit re-exports Foundation.  If you link with
            -framework Cocoa and use a symbol from Foundation, the linker will
            implicitly add a load command to load Foundation and encode the symbol as
            coming from Foundation.  If you use this option, the linker will not add
            a load command for Foundation and encode the symbol as coming from Cocoa.
            Then at runtime dyld will have to search Cocoa and AppKit before finding
            the symbol in Foundation.

[int3]

restrict TAPI re-exports from referring to documents in other TBD files

[smeenai]

LGTM. Thanks for limiting re-exports to sub-documents in the same TBD!

lld/MachO/InputFiles.cpp

370

Nit: make this static.

lld/test/MachO/reexport-stub.s

16

Ah, good find.

[leonardchan]

Hi! I believe our mac builders are failing after this change with

FAIL: lld :: MachO/invalid/stub-link.s (2106 of 2478)
******************** TEST 'lld :: MachO/invalid/stub-link.s' FAILED ********************
Script:
--
: 'RUN: at line 3';   mkdir -p /b/s/w/ir/k/staging/llvm_build/tools/lld/test/MachO/invalid/Output/stub-link.s.tmp
: 'RUN: at line 5';   /b/s/w/ir/k/staging/llvm_build/bin/llvm-mc -filetype obj -triple x86_64-apple-ios /b/s/w/ir/k/llvm-project/lld/test/MachO/invalid/stub-link.s -o /b/s/w/ir/k/staging/llvm_build/tools/lld/test/MachO/invalid/Output/stub-link.s.tmp/test.o
: 'RUN: at line 6';   not lld -flavor darwinnew -o /b/s/w/ir/k/staging/llvm_build/tools/lld/test/MachO/invalid/Output/stub-link.s.tmp/test -Z -L/b/s/w/ir/k/llvm-project/lld/test/MachO/invalid/../Inputs/iPhoneSimulator.sdk/usr/lib -lSystem /b/s/w/ir/k/staging/llvm_build/tools/lld/test/MachO/invalid/Output/stub-link.s.tmp/test.o 2>&1 | /b/s/w/ir/k/staging/llvm_build/bin/FileCheck /b/s/w/ir/k/llvm-project/lld/test/MachO/invalid/stub-link.s
--
Exit Code: 1

Command Output (stderr):
--
/b/s/w/ir/k/llvm-project/lld/test/MachO/invalid/stub-link.s:8:14: error: CHECK-DAG: expected string not found in input
# CHECK-DAG: error: undefined symbol __cache_handle_memory_pressure_event
             ^
<stdin>:1:1: note: scanning from here
lld: error: undefined symbol _from_non_reexported_tapi_dylib, referenced from test.o
^
<stdin>:1:6: note: possible intended match here
lld: error: undefined symbol _from_non_reexported_tapi_dylib, referenced from test.o
     ^

Input file: <stdin>
Check file: /b/s/w/ir/k/llvm-project/lld/test/MachO/invalid/stub-link.s

-dump-input=help explains the following input dump.

Input was:
<<<<<<
         1: lld: error: undefined symbol _from_non_reexported_tapi_dylib, referenced from test.o
dag:8'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
dag:8'1          ?                                                                               possible intended match
>>>>>>

--

I see that you sent out a fix for the objc.s test. Would you mind taking a look at this one? Thanks.

Builder: https://luci-milo.appspot.com/p/fuchsia/builders/ci/clang-mac-x64/b8870848238102897488?

[int3]

Hmm, oddly enough the LLVM buildbots seem ok with it. But @thakis also mentioned the build failure on D86180: [lld-macho] Make it possible to re-export .tbd files...

I'm kicking off a build on another machine now. If I still can't figure it out in a bit I'll disable the test.

lld/MachO/CMakeLists.txt

 set(LLVM_TARGET_DEFINITIONS Options.td)
 tablegen(LLVM Options.inc -gen-opt-parser-defs)
 add_public_tablegen_target(MachOOptionsTableGen)
 
 add_lld_library(lldMachO2
   Arch/X86_64.cpp
   Driver.cpp
+  DriverUtils.cpp
   ExportTrie.cpp
   InputFiles.cpp
   InputSection.cpp
   MergedOutputSection.cpp
   OutputSection.cpp
   OutputSegment.cpp
   SymbolTable.cpp
   Symbols.cpp

lld/MachO/Config.h

struct Configuration {
   Symbol *entry;
   bool hasReexports = false;
   uint32_t headerPad;
   llvm::StringRef installName;
   llvm::StringRef outputFile;
   llvm::MachO::Architecture arch;
   PlatformInfo platform;
   llvm::MachO::HeaderFileType outputType;
+  std::vector<llvm::StringRef> systemLibraryRoots;
   std::vector<llvm::StringRef> librarySearchPaths;
   std::vector<llvm::StringRef> frameworkSearchPaths;
   std::vector<llvm::StringRef> runtimePaths;
   llvm::DenseMap<llvm::StringRef, SymbolPriorityEntry> priorities;
 };
 
 // The symbol with the highest priority should be ordered first in the output
 // section (modulo input section contiguity constraints). Using priority

lld/MachO/Driver.cpp

 //===- Driver.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 "Driver.h"
 #include "Config.h"
+#include "DriverUtils.h"
 #include "InputFiles.h"
 #include "OutputSection.h"
 #include "OutputSegment.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
 #include "SyntheticSections.h"
 #include "Target.h"
 #include "Writer.h"
if (!suffix.empty()) {
         // only append suffix if realpath() succeeds
         Twine suffixed = location + suffix;
         if (fs::exists(suffixed))
           return suffixed.str();
       }
       // Suffix lookup failed, fall through to the no-suffix case.
     }
 
-    if (Optional<std::string> path = findWithExtension(symlink, {".tbd", ""}))
+    if (Optional<std::string> path = resolveDylibPath(symlink))
       return path;
   }
   return {};
 }
 
 static TargetInfo *createTargetInfo(opt::InputArgList &args) {
   StringRef arch = args.getLastArgValue(OPT_arch, "x86_64");
   config->arch = llvm::MachO::getArchitectureFromName(
if (path::is_absolute(path, path::Style::posix)) {
         path::append(buffer, path);
         // Do not warn about paths that are computed via the syslib roots
         if (fs::is_directory(buffer)) {
           paths.push_back(saver.save(buffer.str()));
           found = true;
         }
       }
     }
     if (!found && warnIfNotDirectory(optionLetter, path))
       paths.push_back(path);
   }
 
   // `-Z` suppresses the standard "system" search paths.
   if (args.hasArg(OPT_Z))
     return;
 
   for (auto const &path : systemPaths) {
static void addFile(StringRef path) {
   }
   case file_magic::macho_object:
     inputFiles.push_back(make<ObjFile>(mbref));
     break;
   case file_magic::macho_dynamically_linked_shared_lib:
     inputFiles.push_back(make<DylibFile>(mbref));
     break;
   case file_magic::tapi_file: {
-    Expected<std::unique_ptr<InterfaceFile>> result = TextAPIReader::get(mbref);
-    if (!result) {
-      error("could not load TAPI file at " + mbref.getBufferIdentifier() +
-            ": " + toString(result.takeError()));
+    Optional<DylibFile *> dylibFile = makeDylibFromTAPI(mbref);
+    if (!dylibFile)
       return;
-    }
-    inputFiles.push_back(make<DylibFile>(**result));
+    inputFiles.push_back(*dylibFile);
     break;
   }
   default:
     error(path + ": unhandled file type");
   }
 }
 
 static void addFileList(StringRef path) {

 // We expect sub-library names of the form "libfoo", which will match a dylib
 // with a path of .*/libfoo.{dylib, tbd}.
 // XXX ld64 seems to ignore the extension entirely when matching sub-libraries;
 // I'm not sure what the use case for that is.
 static bool markSubLibrary(StringRef searchName) {
   for (InputFile *file : inputFiles) {
     if (auto *dylibFile = dyn_cast<DylibFile>(file)) {
       StringRef filename = path::filename(dylibFile->getName());
       if (filename.consume_front(searchName) &&
           (filename == ".dylib" || filename == ".tbd")) {
         dylibFile->reexport = true;
         return true;
       }
     }
   }
   return false;
 }
 
 static inline char toLowerDash(char x) {
bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
   config->entry = symtab->addUndefined(args.getLastArgValue(OPT_e, "_main"));
   config->outputFile = args.getLastArgValue(OPT_o, "a.out");
   config->installName =
       args.getLastArgValue(OPT_install_name, config->outputFile);
   config->headerPad = args::getHex(args, OPT_headerpad, /*Default=*/32);
   config->outputType = args.hasArg(OPT_dylib) ? MH_DYLIB : MH_EXECUTE;
   config->runtimePaths = args::getStrings(args, OPT_rpath);
 
-  std::vector<StringRef> roots;
+  std::vector<StringRef> &roots = config->systemLibraryRoots;
   for (const Arg *arg : args.filtered(OPT_syslibroot))
     roots.push_back(arg->getValue());
   // NOTE: the final `-syslibroot` being `/` will ignore all roots
   if (roots.size() && roots.back() == "/")
     roots.clear();
   // NOTE: roots can never be empty - add an empty root to simplify the library
   // and framework search path computation.
   if (roots.empty())

lld/MachO/DriverUtils.h

+//===- DriverUtils.h --------------------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_MACHO_DRIVER_UTILS_H
+#define LLD_MACHO_DRIVER_UTILS_H
+
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/MemoryBuffer.h"
+
+namespace lld {
+namespace macho {
+
+class DylibFile;
+
+// Check for both libfoo.dylib and libfoo.tbd (in that order).
+llvm::Optional<std::string> resolveDylibPath(llvm::StringRef path);
+
+llvm::Optional<DylibFile *> makeDylibFromTAPI(llvm::MemoryBufferRef mbref,
+                                              DylibFile *umbrella = nullptr);
+
+} // namespace macho
+} // namespace lld
+
+#endif

lld/MachO/DriverUtils.cpp

+//===- DriverUtils.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 "DriverUtils.h"
+#include "InputFiles.h"
+
+#include "lld/Common/ErrorHandler.h"
+#include "lld/Common/Memory.h"
+#include "llvm/Support/Path.h"
+#include "llvm/TextAPI/MachO/TextAPIReader.h"
+
+using namespace llvm;
+using namespace llvm::MachO;
+using namespace llvm::sys;
+using namespace lld;
+using namespace lld::macho;
+
+Optional<std::string> macho::resolveDylibPath(StringRef path) {
+  // TODO: if a tbd and dylib are both present, we should check to make sure
+  // they are consistent.
+  if (fs::exists(path))
+    return std::string(path);
+
+  SmallString<261> location = path;
+  path::replace_extension(location, ".tbd");
+  if (fs::exists(location))
+    return std::string(location);
+
+  return {};
+}
+
+Optional<DylibFile *> macho::makeDylibFromTAPI(MemoryBufferRef mbref,
+                                               DylibFile *umbrella) {
+  Expected<std::unique_ptr<InterfaceFile>> result = TextAPIReader::get(mbref);
+  if (!result) {
+    error("could not load TAPI file at " + mbref.getBufferIdentifier() + ": " +
+          toString(result.takeError()));
+    return {};
+  }
+  return make<DylibFile>(**result, umbrella);
+}

lld/MachO/InputFiles.cpp

 //
 // Without the above differences, I think you can use your knowledge about ELF
 // and COFF for Mach-O.
 //
 //===----------------------------------------------------------------------===//
 
 #include "InputFiles.h"
 #include "Config.h"
+#include "DriverUtils.h"
 #include "ExportTrie.h"
 #include "InputSection.h"
 #include "MachOStructs.h"
 #include "OutputSection.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
 #include "Target.h"
 
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Memory.h"
+#include "llvm/ADT/iterator.h"
 #include "llvm/BinaryFormat/MachO.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 
 using namespace llvm;
 using namespace llvm::MachO;
 using namespace llvm::support::endian;
ObjFile::ObjFile(MemoryBufferRef mb) : InputFile(ObjKind, mb) {
   }
 
   // The relocations may refer to the symbols, so we parse them after we have
   // parsed all the symbols.
   for (size_t i = 0, n = subsections.size(); i < n; ++i)
     parseRelocations(sectionHeaders[i], subsections[i]);
 }
 
+// The path can point to either a dylib or a .tbd file.
+static Optional<DylibFile *> loadDylib(StringRef path, DylibFile *umbrella) {
+  Optional<MemoryBufferRef> mbref = readFile(path);
+  if (!mbref) {
+    error("could not read dylib file at " + path);
+    return {};
+  }
+
+  file_magic magic = identify_magic(mbref->getBuffer());
+  if (magic == file_magic::tapi_file)
+    return makeDylibFromTAPI(*mbref, umbrella);
+  assert(magic == file_magic::macho_dynamically_linked_shared_lib);
+  return make<DylibFile>(*mbref, umbrella);
+}
+
+// TBD files are parsed into a series of TAPI documents (InterfaceFiles), with
+// the first document storing child pointers to the rest of them. When we are
+// processing a given TBD file, we store that top-level document here. When
+// processing re-exports, we search its children for potentially matching
+// documents in the same TBD file. Note that the children themselves don't
+// point to further documents, i.e. this is a two-level tree.
+//
+// ld64 allows a TAPI re-export to reference documents nested within other TBD
+// files, but that seems like a strange design, so this is an intentional
+// deviation.
+const InterfaceFile *currentTopLevelTapi = nullptr;
+
+// Re-exports can either refer to on-disk files, or to documents within .tbd
+// files.
+static Optional<DylibFile *> loadReexport(StringRef path, DylibFile *umbrella) {
+  if (path::is_absolute(path, path::Style::posix))
+    for (StringRef root : config->systemLibraryRoots)
+      if (Optional<std::string> dylibPath =
+              resolveDylibPath((root + path).str()))
+        return loadDylib(*dylibPath, umbrella);
+
+  // TODO: Expand @loader_path, @executable_path etc
+
+  if (currentTopLevelTapi != nullptr) {
+    for (InterfaceFile &child :
+         make_pointee_range(currentTopLevelTapi->documents())) {
+      if (path == child.getInstallName())
+        return make<DylibFile>(child, umbrella);
+      assert(child.documents().empty());
+    }
+  }
+
+  if (Optional<std::string> dylibPath = resolveDylibPath(path))
+    return loadDylib(*dylibPath, umbrella);
+
+  error("unable to locate re-export with install name " + path);
+  return {};
+}
+
 DylibFile::DylibFile(MemoryBufferRef mb, DylibFile *umbrella)
     : InputFile(DylibKind, mb) {
   if (umbrella == nullptr)
     umbrella = this;
 
   auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
   auto *hdr = reinterpret_cast<const mach_header_64 *>(mb.getBufferStart());
 
   // Initialize dylibName.
   if (const load_command *cmd = findCommand(hdr, LC_ID_DYLIB)) {
     auto *c = reinterpret_cast<const dylib_command *>(cmd);
     dylibName = reinterpret_cast<const char *>(cmd) + read32le(&c->dylib.name);
   } else {
     error("dylib " + getName() + " missing LC_ID_DYLIB load command");
     return;
   }
 
   // Initialize symbols.
+  // TODO: if a re-exported dylib is public (lives in /usr/lib or
+  // /System/Library/Frameworks), we should bind to its symbols directly
+  // instead of the re-exporting umbrella library.
   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) {
                 bool isWeakDef = flags & EXPORT_SYMBOL_FLAGS_WEAK_DEFINITION;
                 bool isTlv = flags & EXPORT_SYMBOL_FLAGS_KIND_THREAD_LOCAL;
                 symbols.push_back(symtab->addDylib(saver.save(name), umbrella,
                                                    isWeakDef, isTlv));
for (uint32_t i = 0, n = hdr->ncmds; i < n; ++i) {
     auto *cmd = reinterpret_cast<const load_command *>(p);
     p += cmd->cmdsize;
     if (cmd->cmd != LC_REEXPORT_DYLIB)
       continue;
 
     auto *c = reinterpret_cast<const dylib_command *>(cmd);
     StringRef reexportPath =
         reinterpret_cast<const char *>(c) + read32le(&c->dylib.name);
-    // TODO: Expand @loader_path, @executable_path etc in reexportPath
-    Optional<MemoryBufferRef> buffer = readFile(reexportPath);
-    if (!buffer) {
-      error("unable to read re-exported dylib at " + reexportPath);
-      return;
-    }
-    reexported.push_back(make<DylibFile>(*buffer, umbrella));
+    if (Optional<DylibFile *> reexport = loadReexport(reexportPath, umbrella))
+      reexported.push_back(*reexport);
   }
 }
 
 DylibFile::DylibFile(const InterfaceFile &interface, DylibFile *umbrella)
     : InputFile(DylibKind, interface) {
   if (umbrella == nullptr)
     umbrella = this;
 
for (const auto symbol : interface.symbols()) {
     case SymbolKind::ObjectiveCClassEHType:
       addSymbol("_OBJC_EHTYPE_$_" + symbol->getName());
       break;
     case SymbolKind::ObjectiveCInstanceVariable:
       addSymbol("_OBJC_IVAR_$_" + symbol->getName());
       break;
     }
   }
-  // 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 (const std::shared_ptr<InterfaceFile> &intf : interface.documents())
-    reexported.push_back(make<DylibFile>(*intf, umbrella));
+
+  bool isTopLevelTapi = false;
+  if (currentTopLevelTapi == nullptr) {
+    currentTopLevelTapi = &interface;
+    isTopLevelTapi = true;
+  }
+
+  for (InterfaceFileRef intfRef : interface.reexportedLibraries())
+    if (Optional<DylibFile *> reexport =
+            loadReexport(intfRef.getInstallName(), umbrella))
+      reexported.push_back(*reexport);
+
+  if (isTopLevelTapi)
+    currentTopLevelTapi = nullptr;
 }
 
 ArchiveFile::ArchiveFile(std::unique_ptr<llvm::object::Archive> &&f)
     : InputFile(ArchiveKind, f->getMemoryBufferRef()), file(std::move(f)) {
   for (const object::Archive::Symbol &sym : file->symbols())
     symtab->addLazy(sym.getName(), this, sym);
 }
 

lld/test/MachO/Inputs/MacOSX.sdk/usr/lib/libc++.tbd

 --- !tapi-tbd-v3
 archs:            [ i386, x86_64 ]
-uuids:            [ 'i386: 00000000-0000-0000-0000-000000000000', 'x86_64: 00000000-0000-0000-0000-0
-0000000001' ]
+uuids:            [ 'i386: 00000000-0000-0000-0000-000000000000', 'x86_64: 00000000-0000-0000-0000-000000000001' ]
 platform:         macosx
 install-name:     '/usr/lib/libc++.dylib'
 current-version:  1281
 exports:
   - archs:        [ i386, x86_64 ]
+    re-exports:   [ '/usr/lib/libc++abi.dylib' ]
 ...

lld/test/MachO/Inputs/MacOSX.sdk/usr/lib/libc++abi.tbd

 --- !tapi-tbd-v3
 archs:            [ i386, x86_64 ]
-uuids:            [ 'i386: 00000000-0000-0000-0000-000000000000', 'x86_64: 00000000-0000-0000-0000-0
-0000000001' ]
+uuids:            [ 'i386: 00000000-0000-0000-0000-000000000000', 'x86_64: 00000000-0000-0000-0000-000000000001' ]
 platform:         macosx
-install-name:     '/usr/lib/libc++.dylib'
+install-name:     '/usr/lib/libc++abi.dylib'
 current-version:  1281
 exports:
   - archs:        [ i386, x86_64 ]
+    symbols:      [ ___gxx_personality_v0 ]
 ...

lld/test/MachO/Inputs/iPhoneSimulator.sdk/usr/lib/libSystem.tbd

 install-name:     '/usr/lib/libcache.dylib'
 current-version:  83
 parent-umbrella:  System
 exports:
   - archs:      [ i386 ]
     symbols:    [ __cache_handle_memory_pressure_event ]
   - archs:      [ i386, x86_64 ]
     symbols:    [ _cache_create, _cache_destroy, _cache_get ]
+
+# The following TAPI document is not re-exported by any other document in this
+# TBD file, and should therefore be inaccessible.
+--- !tapi-tbd-v3
+archs:            [ i386, x86_64 ]
+uuids:            [ 'i386: 00000000-0000-0000-0000-000000000003', 'x86_64: 00000000-0000-0000-0000-000000000004' ]
+platform:         ios
+install-name:     '/usr/lib/libnotreexported.dylib'
+exports:
+  - archs:      [ i386, x86_64 ]
+    symbols:    [ _from_non_reexported_tapi_dylib ]
 ...

lld/test/MachO/invalid/stub-link.s

 # REQUIRES: x86
 
 # RUN: mkdir -p %t
 #
 # RUN: llvm-mc -filetype obj -triple x86_64-apple-ios %s -o %t/test.o
 # RUN: not lld -flavor darwinnew -o %t/test -Z -L%S/../Inputs/iPhoneSimulator.sdk/usr/lib -lSystem %t/test.o 2>&1 | FileCheck %s
 
-# CHECK: error: undefined symbol __cache_handle_memory_pressure_event
+# CHECK-DAG: error: undefined symbol __cache_handle_memory_pressure_event
+# CHECK-DAG: error: undefined symbol _from_non_reexported_tapi_dylib
 
 .section __TEXT,__text
 .global _main
 
 _main:
   movq __cache_handle_memory_pressure_event@GOTPCREL(%rip), %rax
+  movq _from_non_reexported_tapi_dylib@GOTPCREL(%rip), %rax
   ret

lld/test/MachO/reexport-stub.s

 # REQUIRES: x86
 # RUN: mkdir -p %t
 
 ## This test verifies that a non-TBD dylib can re-export a TBD library.
 
 # RUN: echo "" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/reexporter.o
 # RUN: lld -flavor darwinnew -dylib -syslibroot %S/Inputs/MacOSX.sdk -lc++ -sub_library libc++ \
 # RUN:   %t/reexporter.o -o %t/libreexporter.dylib
 # RUN: llvm-objdump --macho --all-headers %t/libreexporter.dylib | FileCheck %s --check-prefix=DYLIB-HEADERS
 # DYLIB-HEADERS:     cmd     LC_REEXPORT_DYLIB
 # DYLIB-HEADERS-NOT: Load command
 # DYLIB-HEADERS:     name    /usr/lib/libc++.dylib
+
+# RUN: llvm-mc -filetype obj -triple x86_64-apple-darwin %s -o %t/test.o
+# RUN: lld -flavor darwinnew -o %t/test -syslibroot %S/Inputs/MacOSX.sdk -lSystem -L%t -lreexporter %t/test.o
+# RUN: llvm-objdump --bind --no-show-raw-insn -d %t/test | FileCheck %s
+
+# CHECK: Bind table:
+# CHECK-DAG: __DATA __data {{.*}} pointer 0 libreexporter ___gxx_personality_v0
+
+.text
+.globl _main
+
+_main:
+  ret
+
+.data
+  .quad ___gxx_personality_v0

lld/test/MachO/stub-link.s

 # REQUIRES: x86
 
 # RUN: mkdir -p %t
 #
 # RUN: llvm-mc -filetype obj -triple x86_64-apple-darwin %s -o %t/test.o
-# RUN: lld -flavor darwinnew -o %t/test -syslibroot %S/Inputs/MacOSX.sdk -lSystem -framework CoreFoundation %t/test.o
+# RUN: lld -flavor darwinnew -o %t/test -syslibroot %S/Inputs/MacOSX.sdk -lSystem -lc++ -framework CoreFoundation %t/test.o
 #
 # RUN: llvm-objdump --bind --no-show-raw-insn -d -r %t/test | FileCheck %s
 
 # CHECK: Disassembly of section __TEXT,__text:
 # CHECK: movq {{.*}} # [[ADDR:[0-9a-f]+]]
 
 # CHECK: Bind table:
 # CHECK-DAG: __DATA_CONST __got 0x[[ADDR]] pointer 0 libSystem ___nan
 # CHECK-DAG: __DATA __data {{.*}} pointer 0 CoreFoundation _OBJC_CLASS_$_NSObject
 # CHECK-DAG: __DATA __data {{.*}} pointer 0 CoreFoundation _OBJC_METACLASS_$_NSObject
 # CHECK-DAG: __DATA __data {{.*}} pointer 0 CoreFoundation _OBJC_IVAR_$_NSConstantArray._count
 # CHECK-DAG: __DATA __data {{.*}} pointer 0 CoreFoundation _OBJC_EHTYPE_$_NSException
+# CHECK-DAG: __DATA __data {{.*}} pointer 0 libc++         ___gxx_personality_v0
 
 .section __TEXT,__text
 .global _main
 
 _main:
+## This symbol is defined in an inner TAPI document within libSystem.tbd.
   movq ___nan@GOTPCREL(%rip), %rax
   ret
 
 .data
   .quad _OBJC_CLASS_$_NSObject
   .quad _OBJC_METACLASS_$_NSObject
   .quad _OBJC_IVAR_$_NSConstantArray._count
   .quad _OBJC_EHTYPE_$_NSException
+
+## This symbol is defined in libc++abi.tbd, but we are linking test.o against
+## libc++.tbd (which re-exports libc++abi). Linking against this symbol verifies
+## that .tbd file re-exports can refer not just to TAPI documents within the
+## same .tbd file, but to other on-disk files as well.
+  .quad ___gxx_personality_v0

lld/test/MachO/sub-library.s

 
 ## Check that we fail gracefully if the sub-library is missing
 # RUN: not lld -flavor darwinnew -dylib -Z -o %t/sub-library -sub_library libmissing %t/sub-library.o 2>&1 \
 # RUN:   | FileCheck %s --check-prefix=MISSING-SUB-LIBRARY
 # MISSING-SUB-LIBRARY: error: -sub_library libmissing does not match a supplied dylib
 # RUN: rm -f %t/libgoodbye.dylib
 # RUN: not lld -flavor darwinnew -o %t/sub-library -Z -L%t -lsuper %t/sub-library.o 2>&1 \
 # RUN:  | FileCheck %s --check-prefix=MISSING-REEXPORT -DDIR=%t
-# MISSING-REEXPORT: error: unable to read re-exported dylib at [[DIR]]/libgoodbye.dylib
+# MISSING-REEXPORT: error: unable to locate re-export with install name [[DIR]]/libgoodbye.dylib
 
 .text
 .globl _main
 
 _main:
   movl $0x2000004, %eax # write() syscall
   mov $1, %rdi # stdout
   movq _hello_world@GOTPCREL(%rip), %rsi