[llvm-nm] Support the -V option, print that the tool is compatible with GNU nm

[mstorsjo]

Summary

This unlocks some codepaths in libtool.

[MaskRay]

llvm/docs/CommandGuide/llvm-nm.rst needs update.

llvm/test/tools/llvm-nm/libtool-version.test

4

Move the file level comment above the commands.

llvm/tools/llvm-nm/llvm-nm.cpp

2241

Does libtool detect the substring GNU nm? If not, the notice should be dropped.

For example, ld.lld prints compatible with GNU linkers just because libtool detects GNU (D31199).

2241

If yes, there needs to be a comment.

[mstorsjo]

In D102321#2754456, @MaskRay wrote:

llvm/docs/CommandGuide/llvm-nm.rst needs update.

Ok, will do

llvm/test/tools/llvm-nm/libtool-version.test

4

Sure, will do

llvm/tools/llvm-nm/llvm-nm.cpp

2241

Libtool detects ”GNU” only, but not necessarily “GNU nm”. Is this wording ok (while adding a comment explaining why) or do you want it written differently?

[MaskRay]

llvm/tools/llvm-nm/llvm-nm.cpp

2241

"llvm-nm, compatible with GNU nm\n" is ok, we just need to document the fact.

[mstorsjo]

Addressed the feedback.

[MaskRay]

Looks great! Please wait for @jhenderson

llvm/test/tools/llvm-nm/libtool-version.test

7

Add CHECK: LLVM version

(See some similar --version tests)

[jhenderson]

Looks good, with a couple of nits.

llvm/docs/CommandGuide/llvm-nm.rst

234–236

Perhaps change the end of the description here to something like "... executable, then exit." The exiting aspect I think deserves describing, since llvm-nm doesn't need any other commands to still do useful work on an object normally.

llvm/test/tools/llvm-nm/libtool-version.test

2–3

I know they're not strictly necessary here, but I'd add some comment markers to make the comments stand out from the rest of the test.

[mstorsjo]

Thanks for the reviews!

llvm/docs/CommandGuide/llvm-nm.rst

234–236

Ok, amending that.

llvm/test/tools/llvm-nm/libtool-version.test

2–3

Sure, will do

llvm/docs/CommandGuide/llvm-nm.rst

 .. option:: --special-syms
 
  Do not filter special symbols from the output.
 
 .. option:: --undefined-only, -u
 
  Print only undefined symbols.
 
-.. option:: --version
+.. option:: --version, -V
 
- Display the version of the :program:`llvm-nm` executable. Does not stack with
- other commands.
+ Display the version of the :program:`llvm-nm` executable, then exit. Does not
+ stack with other commands.
 
 .. option:: --without-aliases
 
  Exclude aliases from the output.
 
 .. option:: @<FILE>
 
  Read command-line options from response file `<FILE>`.

llvm/test/tools/llvm-nm/libtool-version.test

+# Check that the output of llvm-nm -V (and --version) contains the text
+# "GNU" somewhere, to let libtool know that it is compatible with GNU nm.
+# Also check that it contains the LLVM version.
+
+RUN: llvm-nm -V | FileCheck %s
+RUN: llvm-nm --version | FileCheck %s
+CHECK: LLVM version
+CHECK: GNU

llvm/tools/llvm-nm/llvm-nm.cpp

cl::opt<bool> NoLLVMBitcode("no-llvm-bc",
                             cl::desc("Disable LLVM bitcode reader"),
                             cl::cat(NMCat));
 
 cl::opt<bool> AddInlinedInfo("add-inlinedinfo",
                              cl::desc("Add symbols from the inlined libraries, "
                                       "TBD(Mach-O) only"),
                              cl::cat(NMCat));
 
+cl::opt<bool> Version("V", cl::desc("Print version info"), cl::cat(NMCat));
+
 cl::extrahelp HelpResponse("\nPass @FILE as argument to read options from FILE.\n");
 
 bool PrintAddress = true;
 
 bool MultipleFiles = false;
 
 bool HadError = false;
 
if (!MachOPrintSizeWarning && PrintSize &&  isa<MachOObjectFile>(O)) {
       MachOPrintSizeWarning = true;
     }
     if (!checkMachOAndArchFlags(O, Filename))
       return;
     dumpSymbolNamesFromObject(*O, true);
   }
 }
 
+static void printExtraVersionInfo(raw_ostream &Outs) {
+  // This needs to contain the word "GNU", libtool looks for that string.
+  Outs << "llvm-nm, compatible with GNU nm\n";
+}
+
 int main(int argc, char **argv) {
   InitLLVM X(argc, argv);
   cl::HideUnrelatedOptions(NMCat);
+  cl::AddExtraVersionPrinter(printExtraVersionInfo);
   cl::ParseCommandLineOptions(argc, argv, "llvm symbol table dumper\n");
 
+  if (Version) {
+    cl::PrintVersionMessage();
+    printExtraVersionInfo(outs());
+    return 0;
+  }
+
   // llvm-nm only reads binary files.
   if (error(sys::ChangeStdinToBinary()))
     return 1;
 
   // These calls are needed so that we can read bitcode correctly.
   llvm::InitializeAllTargetInfos();
   llvm::InitializeAllTargetMCs();
   llvm::InitializeAllAsmParsers();