[llvm-objcopy][MachO] Support ARM64_RELOC_ADDEND

An ARM64_RELOC_ADDEND relocation reuses the symbol field for the addend value.
We should pass through such relocations.

Reviewed By: alexander-shaposhnikov

Differential Revision: https://reviews.llvm.org/D104967

Author: MaskRay

llvm/test/tools/llvm-objcopy/MachO/arm64-relocs.s

@@ -0,0 +1,16 @@
+# REQUIRES: aarch64-registered-target
+
+# RUN: llvm-mc -filetype=obj -triple=arm64-apple-darwin %s -o %t
+# RUN: llvm-objcopy %t %t.copy
+# RUN: cmp %t %t.copy
+
+.text
+.globl _foo, _bar
+_foo:
+  ## ARM64_RELOC_ADDEND and ARM64_RELOC_BRANCH26
+  bl _bar + 123
+
+_bar:
+  ret
+
+.subsections_via_symbols

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

@@ -94,6 +94,7 @@ Expected<std::vector<std::unique_ptr<Section>>> static extractSections(
     S.Content =
         StringRef(reinterpret_cast<const char *>(Data->data()), Data->size());
 
+    const uint32_t CPUType = MachOObj.getHeader().cputype;
     S.Relocations.reserve(S.NReloc);
     for (auto RI = MachOObj.section_rel_begin(SecRef->getRawDataRefImpl()),
               RE = MachOObj.section_rel_end(SecRef->getRawDataRefImpl());
@@ -102,6 +103,10 @@ Expected<std::vector<std::unique_ptr<Section>>> static extractSections(
       R.Symbol = nullptr; // We'll fill this field later.
       R.Info = MachOObj.getRelocation(RI->getRawDataRefImpl());
       R.Scattered = MachOObj.isRelocationScattered(R.Info);
+      unsigned Type = MachOObj.getAnyRelocationType(R.Info);
+      // TODO Support CPU_TYPE_ARM.
+      R.IsAddend = !R.Scattered && (CPUType == MachO::CPU_TYPE_ARM64 &&
+                                    Type == MachO::ARM64_RELOC_ADDEND);
       R.Extern = !R.Scattered && MachOObj.getPlainRelocationExternal(R.Info);
       S.Relocations.push_back(R);
     }
@@ -222,7 +227,7 @@ void MachOReader::setSymbolInRelocationInfo(Object &O) const {
   for (LoadCommand &LC : O.LoadCommands)
     for (std::unique_ptr<Section> &Sec : LC.Sections)
       for (auto &Reloc : Sec->Relocations)
-        if (!Reloc.Scattered) {
+        if (!Reloc.Scattered && !Reloc.IsAddend) {
           const uint32_t SymbolNum =
               Reloc.getPlainRelocationSymbolNum(MachOObj.isLittleEndian());
           if (Reloc.Extern) {

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

@@ -261,7 +261,7 @@ void MachOWriter::writeSections() {
              Sec->Content.size());
       for (size_t Index = 0; Index < Sec->Relocations.size(); ++Index) {
         RelocationInfo RelocInfo = Sec->Relocations[Index];
-        if (!RelocInfo.Scattered) {
+        if (!RelocInfo.Scattered && !RelocInfo.IsAddend) {
           const uint32_t SymbolNum = RelocInfo.Extern
                                          ? (*RelocInfo.Symbol)->Index
                                          : (*RelocInfo.Sec)->Index;

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

@@ -180,6 +180,9 @@ struct RelocationInfo {
   Optional<const Section *> Sec;
   // True if Info is a scattered_relocation_info.
   bool Scattered;
+  // True if the type is an ADDEND. r_symbolnum holds the addend instead of a
+  // symbol index.
+  bool IsAddend;
   // True if the r_symbolnum points to a section number (i.e. r_extern=0).
   bool Extern;
   MachO::any_relocation_info Info;