[mach-o] Add support for using export tries

On Darwin at runtime, dyld will prefer to use the export trie of a dylib instead
of the traditional symbol table (which is large and requires a binary search).

This change enables the linker to generate an export trie and to prefer it if
found in a dylib being linked against.  This also simples the yaml for dylibs
because the yaml form of the trie can be reduced to just a sequence of names.

llvm-svn: 217066

1 files changed, 29 insertions, 1 deletions

diff --git a/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryReader.cpp b/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryReader.cpp
index fc43141ca24..6fcee3bf059 100644
--- a/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryReader.cpp
+++ b/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryReader.cpp
@@ -33,6 +33,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/Object/MachO.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -45,6 +46,8 @@
 #include <system_error>
 
 using namespace llvm::MachO;
+using llvm::object::ExportEntry;
+using llvm::object::MachOObjectFile;
 
 namespace lld {
 namespace mach_o {
@@ -231,6 +234,7 @@ readBinary(std::unique_ptr<MemoryBuffer> &mb,
 
   // Walk load commands looking for segments/sections and the symbol table.
   const data_in_code_entry *dataInCode = nullptr;
+  const dyld_info_command *dyldInfo = nullptr;
   uint32_t dataInCodeSize = 0;
   ec = forEachLoadCommand(lcRange, lcCount, swap, is64,
                     [&] (uint32_t cmd, uint32_t size, const char* lc) -> bool {
@@ -406,6 +410,7 @@ readBinary(std::unique_ptr<MemoryBuffer> &mb,
                                             start + read32(swap, ldc->dataoff));
       dataInCodeSize = read32(swap, ldc->datasize);
       }
+      break;
     case LC_LOAD_DYLIB:
     case LC_LOAD_WEAK_DYLIB:
     case LC_REEXPORT_DYLIB:
@@ -417,6 +422,10 @@ readBinary(std::unique_ptr<MemoryBuffer> &mb,
       f->dependentDylibs.push_back(entry);
       }
       break;
+    case LC_DYLD_INFO:
+    case LC_DYLD_INFO_ONLY:
+      dyldInfo = reinterpret_cast<const dyld_info_command*>(lc);
+      break;
     }
     return false;
   });
@@ -434,11 +443,30 @@ readBinary(std::unique_ptr<MemoryBuffer> &mb,
     }
   }
 
+  if (dyldInfo) {
+    // If any exports, extract and add to normalized exportInfo vector.
+    if (dyldInfo->export_size) {
+      const uint8_t *trieStart = reinterpret_cast<const uint8_t*>(start +
+                                                          dyldInfo->export_off);
+      ArrayRef<uint8_t> trie(trieStart, dyldInfo->export_size);
+      for (const ExportEntry &trieExport : MachOObjectFile::exports(trie)) {
+        Export normExport;
+        normExport.name = trieExport.name().copy(f->ownedAllocations);
+        normExport.offset = trieExport.address();
+        normExport.kind = ExportSymbolKind(trieExport.flags() & EXPORT_SYMBOL_FLAGS_KIND_MASK);
+        normExport.flags = trieExport.flags() & ~EXPORT_SYMBOL_FLAGS_KIND_MASK;
+        normExport.otherOffset = trieExport.other();
+        if (!trieExport.otherName().empty())
+          normExport.otherName = trieExport.otherName().copy(f->ownedAllocations);
+        f->exportInfo.push_back(normExport);
+      }
+    }
+  }
+
   return std::move(f);
 }
 
 
-
 class MachOReader : public Reader {
 public:
   MachOReader(MachOLinkingContext &ctx) : _ctx(ctx) {}