From 8fc67fba019505eb9ee542acf74c4a9e86bd1de7 Mon Sep 17 00:00:00 2001
From: Nick Kledzik <kledzik@apple.com>
Date: Wed, 13 Aug 2014 23:55:41 +0000
Subject: [mach-o] Support re-exported dylibs

In general two-level namespace means each program records exactly which dylib
each undefined (imported) symbol comes from.  But, sometimes the implementor
wants to hide the implementation dylib.  For instance libSytem.dylib is the base
dylib all Darwin programs must link with.  A few years ago it was split up
into two dozen dylibs by all are hidden behind libSystem.dylib which re-exports
each sub-dylib.  All clients still think libSystem.dylib is the implementor.

To support this, the linker must load "indirect" dylibs and not just the
"direct" dylibs specified on the command line.  This is done in the
createImplicitFiles() method after all command line specified files are
loaded.  Since an indirect dylib may have already been loaded as a direct dylib
(or indirectly via a previous direct dylib), the MachOLinkingContext keeps
a list of all loaded dylibs.

With this change hello world can now be linked against the real OS or SDK.

llvm-svn: 215605
---
 .../MachO/MachONormalizedFileBinaryReader.cpp      | 45 +++++++++++++++-------
 1 file changed, 32 insertions(+), 13 deletions(-)

(limited to 'lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryReader.cpp')

diff --git a/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryReader.cpp b/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryReader.cpp
index 27162450d64..fc43141ca24 100644
--- a/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryReader.cpp
+++ b/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryReader.cpp
@@ -28,6 +28,7 @@
 
 #include "lld/Core/Error.h"
 #include "lld/Core/LLVM.h"
+#include "lld/Core/SharedLibraryFile.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
@@ -233,8 +234,9 @@ readBinary(std::unique_ptr<MemoryBuffer> &mb,
   uint32_t dataInCodeSize = 0;
   ec = forEachLoadCommand(lcRange, lcCount, swap, is64,
                     [&] (uint32_t cmd, uint32_t size, const char* lc) -> bool {
-    if (is64) {
-      if (cmd == LC_SEGMENT_64) {
+    switch(cmd) {
+    case LC_SEGMENT_64:
+      if (is64) {
         const segment_command_64 *seg =
                               reinterpret_cast<const segment_command_64*>(lc);
         const unsigned sectionCount = (swap
@@ -276,8 +278,9 @@ readBinary(std::unique_ptr<MemoryBuffer> &mb,
           f->sections.push_back(section);
         }
       }
-    } else {
-      if (cmd == LC_SEGMENT) {
+      break;
+    case LC_SEGMENT:
+      if (!is64) {
         const segment_command *seg =
                               reinterpret_cast<const segment_command*>(lc);
         const unsigned sectionCount = (swap
@@ -319,8 +322,8 @@ readBinary(std::unique_ptr<MemoryBuffer> &mb,
           f->sections.push_back(section);
         }
       }
-    }
-    if (cmd == LC_SYMTAB) {
+      break;
+    case LC_SYMTAB: {
       const symtab_command *st = reinterpret_cast<const symtab_command*>(lc);
       const char *strings = start + read32(swap, st->stroff);
       const uint32_t strSize = read32(swap, st->strsize);
@@ -389,15 +392,31 @@ readBinary(std::unique_ptr<MemoryBuffer> &mb,
             f->localSymbols.push_back(sout);
         }
       }
-    } else if (cmd == LC_ID_DYLIB) {
+      }
+      break;
+    case LC_ID_DYLIB: {
       const dylib_command *dl = reinterpret_cast<const dylib_command*>(lc);
       f->installName = lc + read32(swap, dl->dylib.name);
-    } else if (cmd == LC_DATA_IN_CODE) {
+      }
+      break;
+    case LC_DATA_IN_CODE: {
       const linkedit_data_command *ldc =
                             reinterpret_cast<const linkedit_data_command*>(lc);
       dataInCode = reinterpret_cast<const data_in_code_entry*>(
                                             start + read32(swap, ldc->dataoff));
       dataInCodeSize = read32(swap, ldc->datasize);
+      }
+    case LC_LOAD_DYLIB:
+    case LC_LOAD_WEAK_DYLIB:
+    case LC_REEXPORT_DYLIB:
+    case LC_LOAD_UPWARD_DYLIB: {
+      const dylib_command *dl = reinterpret_cast<const dylib_command*>(lc);
+      DependentDylib entry;
+      entry.path = lc + read32(swap, dl->dylib.name);
+      entry.kind = LoadCommandType(cmd);
+      f->dependentDylibs.push_back(entry);
+      }
+      break;
     }
     return false;
   });
@@ -422,7 +441,7 @@ readBinary(std::unique_ptr<MemoryBuffer> &mb,
 
 class MachOReader : public Reader {
 public:
-  MachOReader(MachOLinkingContext::Arch arch) : _arch(arch) {}
+  MachOReader(MachOLinkingContext &ctx) : _ctx(ctx) {}
 
   bool canParse(file_magic magic, StringRef ext,
                 const MemoryBuffer &mb) const override {
@@ -437,7 +456,7 @@ public:
   parseFile(std::unique_ptr<MemoryBuffer> &mb, const Registry &registry,
             std::vector<std::unique_ptr<File>> &result) const override {
     // Convert binary file to normalized mach-o.
-    auto normFile = readBinary(mb, _arch);
+    auto normFile = readBinary(mb, _ctx.arch());
     if (std::error_code ec = normFile.getError())
       return ec;
     // Convert normalized mach-o to atoms.
@@ -450,16 +469,16 @@ public:
     return std::error_code();
   }
 private:
-  MachOLinkingContext::Arch _arch;
+  MachOLinkingContext &_ctx;
 };
 
 
 } // namespace normalized
 } // namespace mach_o
 
-void Registry::addSupportMachOObjects(const MachOLinkingContext &ctx) {
+void Registry::addSupportMachOObjects(MachOLinkingContext &ctx) {
   MachOLinkingContext::Arch arch = ctx.arch();
-  add(std::unique_ptr<Reader>(new mach_o::normalized::MachOReader(arch)));
+  add(std::unique_ptr<Reader>(new mach_o::normalized::MachOReader(ctx)));
   addKindTable(Reference::KindNamespace::mach_o, ctx.archHandler().kindArch(), 
                ctx.archHandler().kindStrings());
   add(std::unique_ptr<YamlIOTaggedDocumentHandler>(
-- 
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