[llvm-readobj] Support -needed-libs option for Mach-O files

[phosek]

Summary

This implements the -needed-libs option functionality in Mach-O dumper.

[phosek]

To give more context, I'm planning on implementing this feature for COFF as well and then using llvm-readobj in D41272 to have a solution that works across all platforms.

[davide]

Can you please add a testcase, Petr?

[phosek]

Done

[phosek]

@davide Is there anything else?

[davide]

I'm across the pond fo the rest of the year, sorry if communication is a little slow :)

tools/llvm-readobj/MachODumper.cpp

42–43

this is Mach-O specific no? So it should be grouped with the others.

687–692

maybe this would be more readable if it used a switch, not sure if it's entirely feasible.

695

static_cast<> and auto *.

701

Why you need this stable sort?

[phosek]

tools/llvm-readobj/MachODumper.cpp

42–43

This should be implemented for all formats, see https://github.com/llvm-mirror/llvm/blob/master/tools/llvm-readobj/ObjDumper.h#L42. It's currently implemented for ELF, I'm trying to add an implementation for Mach-O (D41527) and COFF (D41529).

701

I have followed the ELF implementation which also uses stable sort, I'm not sure why it's used there.

[davide]

LGTM with one comment addressed. Thanks.

tools/llvm-readobj/MachODumper.cpp

701

I'd rather not cargo cult this here unless we have a good reason to. We shouldn't need this call, should we?

[phosek]

tools/llvm-readobj/MachODumper.cpp

701

I think having a stable output order may be useful in some cases. Also if that's what we're already doing for ELF version, we should probably be consistent across all formats?

[davide]

tools/llvm-readobj/MachODumper.cpp

701

I think we should have a stable order of these *regardless*. I'm nervous about adding a call to std::stable_sort() unless we have a good reason for it, because it might hide bugs elsewhere in the reader.

[phosek]

tools/llvm-readobj/MachODumper.cpp

701

Understood, the problem is that load_command() doesn't provide any guarantees about the ordering, the order should be the same as the order in which the commands were read from the file, but commands are also not guaranteed to be sorted and after briefly checking a few binaries they definitely aren't. So the way to guarantee ordering would be to sort LoadCommands in MachOObjectFile constructor when reading the file, is that what you're suggesting?

tools/llvm-readobj/MachODumper.cpp

public:
   void printFileHeaders() override;
   void printSections() override;
   void printRelocations() override;
   void printSymbols() override;
   void printDynamicSymbols() override;
   void printUnwindInfo() override;
   void printStackMap() const override;
 
+  void printNeededLibraries() override;
+
   // MachO-specific.
   void printMachODataInCode() override;
   void printMachOVersionMin() override;
   void printMachODysymtab() override;
   void printMachOSegment() override;
   void printMachOIndirectSymbols() override;
   void printMachOLinkerOptions () override;
 
if (Obj->isLittleEndian())
      prettyPrintStackMap(
                       llvm::outs(),
                       StackMapV2Parser<support::little>(StackMapContentsArray));
   else
      prettyPrintStackMap(llvm::outs(),
                          StackMapV2Parser<support::big>(StackMapContentsArray));
 }
 
+void MachODumper::printNeededLibraries() {
+  ListScope D(W, "NeededLibraries");
+
+  using LibsTy = std::vector<StringRef>;
+  LibsTy Libs;
+
+  for (const auto &Command : Obj->load_commands()) {
+    if (Command.C.cmd == MachO::LC_LOAD_DYLIB ||
+        Command.C.cmd == MachO::LC_ID_DYLIB ||
+        Command.C.cmd == MachO::LC_LOAD_WEAK_DYLIB ||
+        Command.C.cmd == MachO::LC_REEXPORT_DYLIB ||
+        Command.C.cmd == MachO::LC_LAZY_LOAD_DYLIB ||
+        Command.C.cmd == MachO::LC_LOAD_UPWARD_DYLIB) {
+      MachO::dylib_command Dl = Obj->getDylibIDLoadCommand(Command);
+      if (Dl.dylib.name < Dl.cmdsize) {
+        const char *P = (const char *)(Command.Ptr) + Dl.dylib.name;
+        Libs.push_back(P);
+      }
+    }
+  }
+
+  std::stable_sort(Libs.begin(), Libs.end());
+
+  for (const auto &L : Libs) {
+    outs() << "  " << L << "\n";
+  }
+}
+
 void MachODumper::printMachODataInCode() {
   for (const auto &Load : Obj->load_commands()) {
     if (Load.C.cmd  == MachO::LC_DATA_IN_CODE) {
       MachO::linkedit_data_command LLC = Obj->getLinkeditDataLoadCommand(Load);
       DictScope Group(W, "DataInCode");
       W.printNumber("Data offset", LLC.dataoff);
       W.printNumber("Data size", LLC.datasize);
       ListScope D(W, "Data entries");