[llvm-readobj/MachO] Ensure we always have a valid reference to SegmentName

[davide]

Summary

This way we don't end up printing garbage. Found while testing lld-macho.

[davide]

git-clang-format.

[grosbach]

Interesting. Would it be better to change the StringRef to a std::string instead? That way the data structure itself maintains the full info.

[davide]

I think it's a good idea (we should probably do the same for Section, but we can take care of that in a separate commit).

Thanks!

[grosbach]

LGTM

llvm-readobj/MachODumper.cpp

struct MachOSection {
     uint32_t Flags;
     uint32_t Reserved1;
     uint32_t Reserved2;
     uint32_t Reserved3;
   };
 
   struct MachOSegment {
     StringRef CmdName;
-    StringRef SegName;
     uint64_t cmdsize;
     uint64_t vmaddr;
     uint64_t vmsize;
     uint64_t fileoff;
     uint64_t filesize;
     uint32_t maxprot;
     uint32_t initprot;
     uint32_t nsects;

 }
 
 static void getSegment(const MachOObjectFile *Obj,
                        const MachOObjectFile::LoadCommandInfo &L,
                        MachOSegment &Segment) {
   if (!Obj->is64Bit()) {
     MachO::segment_command SC = Obj->getSegmentLoadCommand(L);
     Segment.CmdName = "LC_SEGMENT";
-    Segment.SegName = SC.segname;
     Segment.cmdsize = SC.cmdsize;
     Segment.vmaddr = SC.vmaddr;
     Segment.vmsize = SC.vmsize;
     Segment.fileoff = SC.fileoff;
     Segment.filesize = SC.filesize;
     Segment.maxprot = SC.maxprot;
     Segment.initprot = SC.initprot;
     Segment.nsects = SC.nsects;
     Segment.flags = SC.flags;
     return;
   }
   MachO::segment_command_64 SC = Obj->getSegment64LoadCommand(L);
   Segment.CmdName = "LC_SEGMENT_64";
-  Segment.SegName = SC.segname;
   Segment.cmdsize = SC.cmdsize;
   Segment.vmaddr = SC.vmaddr;
   Segment.vmsize = SC.vmsize;
   Segment.fileoff = SC.fileoff;
   Segment.filesize = SC.filesize;
   Segment.maxprot = SC.maxprot;
   Segment.initprot = SC.initprot;
   Segment.nsects = SC.nsects;
for (const auto &Load : Obj->load_commands()) {
     }
   }
 }
 
 void MachODumper::printMachOSegment() {
   for (const auto &Load : Obj->load_commands()) {
     if (Load.C.cmd == MachO::LC_SEGMENT || Load.C.cmd == MachO::LC_SEGMENT_64) {
       MachOSegment MOSegment;
+      StringRef SegName;
       getSegment(Obj, Load, MOSegment);
+      if (!Obj->is64Bit()) {
+        MachO::segment_command SC = Obj->getSegmentLoadCommand(Load);
+        SegName = SC.segname;
+      } else {
+        MachO::segment_command_64 SC = Obj->getSegment64LoadCommand(Load);
+        SegName = SC.segname;
+      }
       DictScope Group(W, "Segment");
       W.printString("Cmd", MOSegment.CmdName);
-      W.printString("Name", MOSegment.SegName);
+      W.printString("Name", SegName);
       W.printNumber("Size", MOSegment.cmdsize);
       W.printHex("vmaddr", MOSegment.vmaddr);
       W.printHex("vmsize", MOSegment.vmsize);
       W.printNumber("fileoff", MOSegment.fileoff);
       W.printNumber("filesize", MOSegment.filesize);
       W.printString("maxprot", getMask(MOSegment.maxprot));
       W.printString("initprot", getMask(MOSegment.initprot));
       W.printNumber("nsects", MOSegment.nsects);