[macho2yaml] Fixup offset for nodes in export trie.

[cishida]

Summary

The offset recorded in export trie nodes is used to capture symbol
information like address and node size. This offset should be relative to the
root of the trie. This updates to processExportNode to follow that
expectation.

[pete]

LGTM

[steven_wu]

LGTM

[cishida]

Start test at clean state & verify against PR test.

llvm/test/tools/obj2yaml/MachO/simple-exporttrie.yaml

+# Test that obj2yaml + yaml2obj can round-trip mach-o library simple export trie entries.
+#
+# RUN: rm -rf %t &&  mkdir -p %t
+# RUN: yaml2obj %s -o %t/libfoo.dylib | FileCheck %s --allow-empty --implicit-check-not warning: --implicit-check-not error:
+# RUN: llvm-nm --dyldinfo-only %t/libfoo.dylib | FileCheck %s --check-prefix=NM
+# NM: 3fb0 T _foo
+
+# RUN: obj2yaml %t/libfoo.dylib | FileCheck %s --check-prefix=YAML
+# YAML: LinkEditData:
+# YAML-NEXT:  ExportTrie:
+# YAML:    Children:
+#YAML-NEXT:      - TerminalSize:    3
+#YAML-NEXT:        NodeOffset:      8
+#YAML-NEXT:        Name:            _foo
+#YAML-NEXT:        Flags:           0x0
+#YAML-NEXT:        Address:         0x3FB0
+#YAML-NEXT:        Other:           0x0
+#YAML-NEXT:        ImportName:      ''
+
+
+
+
+# This file was produced using:
+#  int foo() {return 1;} > tmp.c 
+#  xcrun clang -Wl,-ld64 -isysroot `xcrun --show-sdk-path -sdk macosx` --target=arm64-apple-macos11.3 -dynamiclib -o libfoo.dylib -install_name @rpath/libfoo.dylib tmp.c
+
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x100000C
+  cpusubtype:      0x0
+  filetype:        0x6
+  ncmds:           13
+  sizeofcmds:      680
+  flags:           0x100085
+  reserved:        0x0
+LoadCommands:
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         232
+    segname:         __TEXT
+    vmaddr:          0
+    vmsize:          16384
+    fileoff:         0
+    filesize:        16384
+    maxprot:         5
+    initprot:        5
+    nsects:          2
+    flags:           0
+    Sections:
+      - sectname:        __text
+        segname:         __TEXT
+        addr:            0x3FB0
+        size:            8
+        offset:          0x3FB0
+        align:           2
+        reloff:          0x0
+        nreloc:          0
+        flags:           0x80000400
+        reserved1:       0x0
+        reserved2:       0x0
+        reserved3:       0x0
+        content:         20008052C0035FD6
+      - sectname:        __unwind_info
+        segname:         __TEXT
+        addr:            0x3FB8
+        size:            72
+        offset:          0x3FB8
+        align:           2
+        reloff:          0x0
+        nreloc:          0
+        flags:           0x0
+        reserved1:       0x0
+        reserved2:       0x0
+        reserved3:       0x0
+        content:         010000001C000000000000001C000000000000001C00000002000000B03F00003400000034000000B93F00000000000034000000030000000C000100100001000000000000000002
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         72
+    segname:         __LINKEDIT
+    vmaddr:          16384
+    vmsize:          16384
+    fileoff:         16384
+    filesize:        361
+    maxprot:         1
+    initprot:        1
+    nsects:          0
+    flags:           0
+  - cmd:             LC_ID_DYLIB
+    cmdsize:         48
+    dylib:
+      name:            24
+      timestamp:       1
+      current_version: 0
+      compatibility_version: 0
+    Content:         '@rpath/libfoo.dylib'
+    ZeroPadBytes:    5
+  - cmd:             LC_DYLD_INFO_ONLY
+    cmdsize:         48
+    rebase_off:      0
+    rebase_size:     0
+    bind_off:        0
+    bind_size:       0
+    weak_bind_off:   0
+    weak_bind_size:  0
+    lazy_bind_off:   0
+    lazy_bind_size:  0
+    export_off:      16384
+    export_size:     16
+  - cmd:             LC_SYMTAB
+    cmdsize:         24
+    symoff:          16408
+    nsyms:           2
+    stroff:          16440
+    strsize:         24
+  - cmd:             LC_DYSYMTAB
+    cmdsize:         80
+    ilocalsym:       0
+    nlocalsym:       0
+    iextdefsym:      0
+    nextdefsym:      1
+    iundefsym:       1
+    nundefsym:       1
+    tocoff:          0
+    ntoc:            0
+    modtaboff:       0
+    nmodtab:         0
+    extrefsymoff:    0
+    nextrefsyms:     0
+    indirectsymoff:  0
+    nindirectsyms:   0
+    extreloff:       0
+    nextrel:         0
+    locreloff:       0
+    nlocrel:         0
+  - cmd:             LC_UUID
+    cmdsize:         24
+    uuid:            A2CF51D8-828B-3E0F-B8FA-0DF9C5D1C91A
+  - cmd:             LC_BUILD_VERSION
+    cmdsize:         32
+    platform:        1
+    minos:           721664
+    sdk:             917504
+    ntools:          1
+    Tools:
+      - tool:            3
+        version:         59441152
+  - cmd:             LC_SOURCE_VERSION
+    cmdsize:         16
+    version:         0
+  - cmd:             LC_LOAD_DYLIB
+    cmdsize:         56
+    dylib:
+      name:            24
+      timestamp:       2
+      current_version: 87556096
+      compatibility_version: 65536
+    Content:         '/usr/lib/libSystem.B.dylib'
+    ZeroPadBytes:    6
+  - cmd:             LC_FUNCTION_STARTS
+    cmdsize:         16
+    dataoff:         16400
+    datasize:        8
+  - cmd:             LC_DATA_IN_CODE
+    cmdsize:         16
+    dataoff:         16408
+    datasize:        0
+  - cmd:             LC_CODE_SIGNATURE
+    cmdsize:         16
+    dataoff:         16464
+    datasize:        281
+LinkEditData:
+  ExportTrie:
+    TerminalSize:    0
+    NodeOffset:      0
+    Name:            ''
+    Flags:           0x0
+    Address:         0x0
+    Other:           0x0
+    ImportName:      ''
+    Children:
+      - TerminalSize:    3
+        NodeOffset:      8
+        Name:            _foo
+        Flags:           0x0
+        Address:         0x3FB0
+        Other:           0x0
+        ImportName:      ''
+  NameList:
+    - n_strx:          2
+      n_type:          0xF
+      n_sect:          1
+      n_desc:          0
+      n_value:         16304
+    - n_strx:          7
+      n_type:          0x1
+      n_sect:          0
+      n_desc:          256
+      n_value:         0
+  StringTable:
+    - ' '
+    - _foo
+    - dyld_stub_binder
+  FunctionStarts:  [ 0x3FB0 ]
+...

llvm/tools/obj2yaml/macho2yaml.cpp

  *  | Addr:  0x00000000    |      | Addr:  0x00001160 |
  *  ------------------------      ---------------------
  *
  * This graph represents the trie for the exports "__mh_execute_header" and
  * "_main". In the graph only the "_main" and "__mh_execute_header" nodes are
  * terminal.
 */
 
-const uint8_t *processExportNode(const uint8_t *CurrPtr,
+const uint8_t *processExportNode(const uint8_t *Start, const uint8_t *CurrPtr,
                                  const uint8_t *const End,
                                  MachOYAML::ExportEntry &Entry) {
   if (CurrPtr >= End)
     return CurrPtr;
   unsigned Count = 0;
   Entry.TerminalSize = decodeULEB128(CurrPtr, &Count);
   CurrPtr += Count;
   if (Entry.TerminalSize != 0) {
Entry.Children.insert(Entry.Children.begin(), (size_t)childrenCount,
                         MachOYAML::ExportEntry());
   for (auto &Child : Entry.Children) {
     Child.Name = std::string(reinterpret_cast<const char *>(CurrPtr));
     CurrPtr += Child.Name.length() + 1;
     Child.NodeOffset = decodeULEB128(CurrPtr, &Count);
     CurrPtr += Count;
   }
   for (auto &Child : Entry.Children) {
-    CurrPtr = processExportNode(CurrPtr, End, Child);
+    CurrPtr = processExportNode(Start, Start + Child.NodeOffset, End, Child);
   }
   return CurrPtr;
 }
 
 void MachODumper::dumpExportTrie(std::unique_ptr<MachOYAML::Object> &Y) {
   MachOYAML::LinkEditData &LEData = Y->LinkEdit;
   // The exports trie can be in LC_DYLD_INFO or LC_DYLD_EXPORTS_TRIE
   auto ExportsTrie = Obj.getDyldInfoExportsTrie();
   if (ExportsTrie.empty())
     ExportsTrie = Obj.getDyldExportsTrie();
-  processExportNode(ExportsTrie.begin(), ExportsTrie.end(), LEData.ExportTrie);
+  processExportNode(ExportsTrie.begin(), ExportsTrie.begin(), ExportsTrie.end(),
+                    LEData.ExportTrie);
 }
 
 template <typename nlist_t>
 MachOYAML::NListEntry constructNameList(const nlist_t &nlist) {
   MachOYAML::NListEntry NL;
   NL.n_strx = nlist.n_strx;
   NL.n_type = nlist.n_type;
   NL.n_sect = nlist.n_sect;