[llvm-objcopy][MachO] Implement --redefine-sym and --redefine-syms

Similar to D46029 (ELF) and D70036 (COFF), but for MachO.
Note, when --strip-symbol (not implemented for MachO) is also specified,
--redefine-sym executes before --strip-symbol.

Reviewed By: jhenderson, seiya

Differential Revision: https://reviews.llvm.org/D70212

llvm/test/tools/llvm-objcopy/MachO/redefine-symbol.s

@@ -0,0 +1,51 @@
+# REQUIRES: x86-registered-target
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos %s -o %t
+
+## A non-existent symbol does not error.
+# RUN: llvm-objcopy --redefine-sym _func=_cnuf1234 --redefine-sym _foo=_ba --redefine-sym=_notexist= %t %t2 2>&1 | count 0
+# RUN: llvm-readobj --symbols %t2 | FileCheck %s
+
+# RUN: echo '_func _cnuf1234 #rename func' > %t.rename.txt
+# RUN: echo '  _foo _ba ' >> %t.rename.txt
+# RUN: echo '_notexist _notexist' >> %t.rename.txt
+# RUN: llvm-objcopy --redefine-syms %t.rename.txt %t %t3 2>&1 | count 0
+# RUN: cmp %t2 %t3
+
+# CHECK:      Symbol {
+# CHECK-NEXT:   Name: _ba (1)
+# CHECK-NEXT:   Extern
+# CHECK-NEXT:   Type: Section (0xE)
+# CHECK-NEXT:   Section: __const (0x2)
+# CHECK-NEXT:   RefType: UndefinedNonLazy (0x0)
+# CHECK-NEXT:   Flags [ (0x0)
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Value: 0x0
+# CHECK-NEXT: }
+# CHECK-NEXT: Symbol {
+# CHECK-NEXT:   Name: _cnuf1234 (5)
+# CHECK-NEXT:   Extern
+# CHECK-NEXT:   Type: Section (0xE)
+# CHECK-NEXT:   Section: __text (0x1)
+# CHECK-NEXT:   RefType: UndefinedNonLazy (0x0)
+# CHECK-NEXT:   Flags [ (0x0)
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Value: 0x0
+# CHECK-NEXT: }
+
+## Check that --redefine-sym executes before --strip-symbol.
+# RUN: llvm-objcopy --strip-symbol _foo --redefine-sym _foo=_ba %t %t.notstripped
+# RUN: llvm-readobj --symbols %t.notstripped | FileCheck %s --check-prefix=NOTSTRIPPED
+# NOTSTRIPPED: Name: _ba
+# NOTSTRIPPED: Name: _func
+
+## FIXME: _ba should be stripped after --strip-symbol is implemented.
+# RUN: llvm-objcopy --strip-symbol _ba --redefine-sym _foo=_ba %t %t.noba
+# RUN: llvm-readobj --symbols %t.noba | FileCheck %s --check-prefix=NOTSTRIPPED
+
+.globl _func
+_func:
+
+.section __TEXT,__const
+.globl _foo
+_foo:

llvm/tools/llvm-objcopy/MachO/MachOObjcopy.cpp

@@ -56,7 +56,13 @@ static void markSymbols(const CopyConfig &Config, Object &Obj) {
       (*ISE.Symbol)->Referenced = true;
 }
 
-static void removeSymbols(const CopyConfig &Config, Object &Obj) {
+static void updateAndRemoveSymbols(const CopyConfig &Config, Object &Obj) {
+  for (SymbolEntry &Sym : Obj.SymTable) {
+    auto I = Config.SymbolsToRename.find(Sym.Name);
+    if (I != Config.SymbolsToRename.end())
+      Sym.Name = I->getValue();
+  }
+
   auto RemovePred = [Config](const std::unique_ptr<SymbolEntry> &N) {
     if (N->Referenced)
       return false;
@@ -75,7 +81,7 @@ static Error handleArgs(const CopyConfig &Config, Object &Obj) {
       Config.NewSymbolVisibility || !Config.SymbolsToGlobalize.empty() ||
       !Config.SymbolsToKeep.empty() || !Config.SymbolsToLocalize.empty() ||
       !Config.SymbolsToWeaken.empty() || !Config.SymbolsToKeepGlobal.empty() ||
-      !Config.SectionsToRename.empty() || !Config.SymbolsToRename.empty() ||
+      !Config.SectionsToRename.empty() ||
       !Config.UnneededSymbolsToRemove.empty() ||
       !Config.SetSectionAlignment.empty() || !Config.SetSectionFlags.empty() ||
       Config.ExtractDWO || Config.KeepFileSymbols || Config.LocalizeHidden ||
@@ -95,7 +101,7 @@ static Error handleArgs(const CopyConfig &Config, Object &Obj) {
   if (Config.StripAll)
     markSymbols(Config, Obj);
 
-  removeSymbols(Config, Obj);
+  updateAndRemoveSymbols(Config, Obj);
 
   if (Config.StripAll)
     for (LoadCommand &LC : Obj.LoadCommands)

llvm/tools/llvm-objcopy/MachO/Object.h

@@ -110,6 +110,12 @@ struct SymbolEntry {
 struct SymbolTable {
   std::vector<std::unique_ptr<SymbolEntry>> Symbols;
 
+  using iterator = pointee_iterator<
+      std::vector<std::unique_ptr<SymbolEntry>>::const_iterator>;
+
+  iterator begin() const { return iterator(Symbols.begin()); }
+  iterator end() const { return iterator(Symbols.end()); }
+
   const SymbolEntry *getSymbolByIndex(uint32_t Index) const;
   SymbolEntry *getSymbolByIndex(uint32_t Index);
   void removeSymbols(