Use LC_DYLD_EXPORTS_TRIE to locate the dyld trie structure if present

[jingham]

Summary

The pointer to the dyld trie data structure which lldb needs to parse to get "trampoline kinds" on Darwin used to be a field in the LC_DYLD_INFO load command. A new load command was added recently dedicated to this purpose: LC_DYLD_EXPORTS_TRIE. The format of the trie did not change, however. So all we have to do is use the new command if present. The commands are supposed to be mutually exclusive, so I added an lldb_assert to warn if they are not.

Without this patch TestIndirectSymbols.py fails on systems that use the new command, so there wasn't a need to write a test for this change.

[JDevlieghere]

LGTM

lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp

size_t ObjectFileMachO::ParseSymtab() {
   if (!module_sp)
     return 0;
 
   Progress progress(llvm::formatv("Parsing symbol table for {0}",
                                   m_file.GetFilename().AsCString("<Unknown>")));
 
   llvm::MachO::symtab_command symtab_load_command = {0, 0, 0, 0, 0, 0};
   llvm::MachO::linkedit_data_command function_starts_load_command = {0, 0, 0, 0};
+  llvm::MachO::linkedit_data_command exports_trie_load_command = {0, 0, 0, 0};
   llvm::MachO::dyld_info_command dyld_info = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
   // The data element of type bool indicates that this entry is thumb
   // code.
   typedef AddressDataArray<lldb::addr_t, bool, 100> FunctionStarts;
 
   // Record the address of every function/data that we add to the symtab.
   // We add symbols to the table in the order of most information (nlist
   // records) to least (function starts), and avoid duplicating symbols
case LC_LOAD_UPWARD_DYLIB: {
         if (lc.cmd == LC_REEXPORT_DYLIB) {
           m_reexported_dylibs.AppendIfUnique(file_spec);
         }
 
         dylib_files.Append(file_spec);
       }
     } break;
 
+    case LC_DYLD_EXPORTS_TRIE:
+      exports_trie_load_command.cmd = lc.cmd;
+      exports_trie_load_command.cmdsize = lc.cmdsize;
+      if (m_data.GetU32(&offset, &exports_trie_load_command.dataoff, 2) ==
+          nullptr) // fill in offset and size fields
+        memset(&exports_trie_load_command, 0,
+               sizeof(exports_trie_load_command));
+      break;
     case LC_FUNCTION_STARTS:
       function_starts_load_command.cmd = lc.cmd;
       function_starts_load_command.cmdsize = lc.cmdsize;
       if (m_data.GetU32(&offset, &function_starts_load_command.dataoff, 2) ==
-          nullptr) // fill in symoff, nsyms, stroff, strsize fields
+          nullptr) // fill in data offset and size fields
         memset(&function_starts_load_command, 0,
                sizeof(function_starts_load_command));
       break;
 
     default:
       break;
     }
     offset = cmd_offset + lc.cmdsize;
if (is_local_shared_cache_image) {
       lldb::addr_t linkedit_offset = linkedit_section_sp->GetFileOffset();
       lldb::offset_t linkedit_slide =
           linkedit_offset - m_linkedit_original_offset;
       symtab_load_command.symoff += linkedit_slide;
       symtab_load_command.stroff += linkedit_slide;
       dyld_info.export_off += linkedit_slide;
       m_dysymtab.indirectsymoff += linkedit_slide;
       function_starts_load_command.dataoff += linkedit_slide;
+      exports_trie_load_command.dataoff += linkedit_slide;
     }
 
     nlist_data.SetData(m_data, symtab_load_command.symoff,
                        nlist_data_byte_size);
     strtab_data.SetData(m_data, symtab_load_command.stroff,
                         strtab_data_byte_size);
 
+    // We shouldn't have exports data from both the LC_DYLD_INFO command
+    // AND the LC_DYLD_EXPORTS_TRIE command in the same binary:
+    lldbassert(!((dyld_info.export_size > 0) 
+                 && (exports_trie_load_command.datasize > 0)));
     if (dyld_info.export_size > 0) {
       dyld_trie_data.SetData(m_data, dyld_info.export_off,
                              dyld_info.export_size);
+    } else if (exports_trie_load_command.datasize > 0) {
+      dyld_trie_data.SetData(m_data, exports_trie_load_command.dataoff,
+                             exports_trie_load_command.datasize);
     }
 
     if (m_dysymtab.nindirectsyms != 0) {
       indirect_symbol_index_data.SetData(m_data, m_dysymtab.indirectsymoff,
                                          m_dysymtab.nindirectsyms * 4);
     }
     if (function_starts_load_command.cmd) {
       function_starts_data.SetData(m_data, function_starts_load_command.dataoff,