[lld-macho] Bind re-exported symbols directly to implicitly-linked umbrellas

[int3]

Summary

Suppose we are linking against libFoo, which re-exports the
implicitly-bound libSystem, which in turn re-exports some
non-explicitly-bound library like /usr/lib/system/libsystem_c.dylib.
Then any bindings we have to a symbol in libsystem_c should use
libSystem (and not libFoo) as the umbrella library.

[smeenai]

LGTM

lld/MachO/InputFiles.cpp

for (uint32_t i = 0, n = hdr->ncmds; i < n; ++i) {
     auto *cmd = reinterpret_cast<const load_command *>(p);
     p += cmd->cmdsize;
 
     if (!(hdr->flags & MH_NO_REEXPORTED_DYLIBS) &&
         cmd->cmd == LC_REEXPORT_DYLIB) {
       const auto *c = reinterpret_cast<const dylib_command *>(cmd);
       StringRef reexportPath =
           reinterpret_cast<const char *>(c) + read32le(&c->dylib.name);
-      loadReexport(reexportPath, umbrella, nullptr);
+      loadReexport(reexportPath, exportingFile, nullptr);
     }
 
     // FIXME: What about LC_LOAD_UPWARD_DYLIB, LC_LAZY_LOAD_DYLIB,
     // LC_LOAD_WEAK_DYLIB, LC_REEXPORT_DYLIB (..are reexports from dylibs with
     // MH_NO_REEXPORTED_DYLIBS loaded for -flat_namespace)?
     if (config->namespaceKind == NamespaceKind::flat &&
         cmd->cmd == LC_LOAD_DYLIB) {
       const auto *c = reinterpret_cast<const dylib_command *>(cmd);
case SymbolKind::ObjectiveCInstanceVariable:
       break;
     }
   }
 
   const InterfaceFile *topLevel =
       interface.getParent() == nullptr ? &interface : interface.getParent();
 
   for (InterfaceFileRef intfRef : interface.reexportedLibraries())
-    loadReexport(intfRef.getInstallName(), umbrella, topLevel);
+    loadReexport(intfRef.getInstallName(), exportingFile, topLevel);
 }
 
 ArchiveFile::ArchiveFile(std::unique_ptr<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/implicit-dylibs.s

 # RUN: echo "" | llvm-mc -filetype=obj -triple=x86_64-apple-darwin -o %t/reexporter.o
 
 # RUN: %lld -dylib -lSystem %t/libfoo.o -o %t/libfoo.dylib
 # RUN: %lld -dylib -lSystem %t/libtoplevel.o -o %t/usr/lib/libtoplevel.dylib -install_name /usr/lib/libtoplevel.dylib
 # RUN: %lld -dylib -lSystem %t/libsublevel.o -o %t/usr/lib/system/libsublevel.dylib -install_name /usr/lib/system/libsublevel.dylib
 # RUN: %lld -dylib -lSystem %t/libunused.o -o %t/usr/lib/libunused.dylib -install_name /usr/lib/libunused.dylib
 
 ## Bar.framework is nested within Foo.framework.
-# RUN: %lld -dylib -lSystem %t/framework-baz.o -o %t/System/Library/Frameworks/Foo.framework/Frameworks/Bar.framework/Versions/A/Bar \
+# RUN: %lld -dylib -lSystem %t/framework-bar.o -o %t/System/Library/Frameworks/Foo.framework/Frameworks/Bar.framework/Versions/A/Bar \
 # RUN:   -install_name /System/Library/Frameworks/Foo.framework/Frameworks/Bar.framework/Versions/A/Bar
 # RUN: ln -sf %t/System/Library/Frameworks/Foo.framework/Frameworks/Bar.framework/Versions/A/Bar \
 # RUN:   %t/System/Library/Frameworks/Foo.framework/Frameworks/Bar.framework/Bar
 
 ## Have Foo re-export Bar.
 # RUN: %lld -dylib -F %t/System/Library/Frameworks/Foo.framework/Frameworks \
 # RUN:   -framework Bar -sub_umbrella Bar -lSystem %t/framework-foo.o -o %t/System/Library/Frameworks/Foo.framework/Versions/A/Foo \
 # RUN:   -install_name /System/Library/Frameworks/Foo.framework/Versions/A/Foo
 # RUN: ln -sf %t/System/Library/Frameworks/Foo.framework/Versions/A/Foo %t/System/Library/Frameworks/Foo.framework/Foo
 
-# RUN: %lld -dylib -lSystem %t/framework-bar.o -o %t/Baz.framework/Versions/A/Baz \
+# RUN: %lld -dylib -lSystem %t/framework-baz.o -o %t/Baz.framework/Versions/A/Baz \
 # RUN:   -install_name %t/Baz.framework/Versions/A/Baz
 # RUN: ln -sf %t/Baz.framework/Versions/A/Baz %t/Baz.framework/Baz
 
 # RUN: %lld -dylib -syslibroot %t -framework Foo -F %t -framework Baz \
 # RUN:   -lc++ -ltoplevel -lunused %t/usr/lib/system/libsublevel.dylib %t/libfoo.dylib \
 # RUN:   -sub_library libc++ -sub_library libfoo -sub_library libtoplevel \
 # RUN:   -sub_library libsublevel -sub_library libunused \
 # RUN:   -sub_umbrella Baz -sub_umbrella Foo \
 # RUN:   %t/reexporter.o -o %t/libreexporter.dylib
 
 # RUN: llvm-mc -filetype obj -triple x86_64-apple-darwin %t/test.s -o %t/test.o
 # RUN: %lld -syslibroot %t -o %t/test -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 _foo
 # CHECK-DAG: __DATA __data {{.*}} pointer 0 libtoplevel   _toplevel
 # CHECK-DAG: __DATA __data {{.*}} pointer 0 libreexporter _sublevel
 # CHECK-DAG: __DATA __data {{.*}} pointer 0 Foo           _framework_foo
-# CHECK-DAG: __DATA __data {{.*}} pointer 0 libreexporter _framework_bar
+# CHECK-DAG: __DATA __data {{.*}} pointer 0 Foo           _framework_bar
 # CHECK-DAG: __DATA __data {{.*}} pointer 0 libreexporter _framework_baz
 # CHECK-DAG: __DATA __data {{.*}} pointer 0 libc++abi     ___gxx_personality_v0
 
 # RUN: llvm-objdump --macho --all-headers %t/test | FileCheck %s \
 # RUN:   --check-prefix=LOAD -DDIR=%t --implicit-check-not LC_LOAD_DYLIB
 ## Check that we don't create duplicate LC_LOAD_DYLIBs.
 # RUN: %lld -syslibroot %t -o %t/test -lSystem -L%t -lreexporter -ltoplevel %t/test.o
 # RUN: llvm-objdump --macho --all-headers %t/test | FileCheck %s \