[llvm-jitlink] Add target override option to cli

[Eymay]

Summary

Triple override option is added to finely control target-specific operations like disassembling in tests.

[Eymay]

avoided redefinition of TT

[Eymay]

correct title tag

[Eymay]

Triple override is necessary for targets that do not have a clear architecture signature in their object files. Here you can see the issue on Thumb disassembly.

[lhames]

@Eymay and I discussed this on discord and he's going to look at extending RuntimeDyldChecker to support mixed arm / thumb code -- if that works this will not be necessary, but we can leave it open as a fallback option.

[sgraenitz]

Thanks! LGTM. Yes let's keep this on hold for now and attempt the RuntimeDyldChecker change first.

llvm/tools/llvm-jitlink/llvm-jitlink.cpp

2005

The comment is easy to misunderstand. Can we swap the phrase like this?

Infer the target and override TT if triple is given by user

2007

Please run this through a git clang-format HEAD^? :)

[Eymay]

Addressed feedback

[Eymay]

reword comment and reformat code

llvm/tools/llvm-jitlink/llvm-jitlink.cpp

LoadHidden("load_hidden",
                cl::desc("Link against library X with hidden visibility"),
                cl::cat(JITLinkCategory));
 
 static cl::opt<bool> SearchSystemLibrary(
     "search-sys-lib",
     cl::desc("Add system library paths to library search paths"),
     cl::init(false), cl::cat(JITLinkCategory));
 
+static cl::opt<std::string>
+    TripleName("triple",
+               cl::desc("Override the detected target triple for disassembler"),
+               cl::cat(JITLinkCategory));
+
 static cl::opt<bool> NoExec("noexec", cl::desc("Do not execute loaded code"),
                             cl::init(false), cl::cat(JITLinkCategory));
 
 static cl::list<std::string>
     CheckFiles("check", cl::desc("File containing verifier checks"),
                cl::cat(JITLinkCategory));
 
 static cl::opt<std::string>
int main(int argc, char *argv[]) {
   cl::HideUnrelatedOptions({&JITLinkCategory, &getColorCategory()});
   cl::ParseCommandLineOptions(argc, argv, "llvm jitlink tool");
   ExitOnErr.setBanner(std::string(argv[0]) + ": ");
 
   /// If timers are enabled, create a JITLinkTimers instance.
   std::unique_ptr<JITLinkTimers> Timers =
       ShowTimes ? std::make_unique<JITLinkTimers>() : nullptr;
 
+  // Infer the target and override TT if triple is given by user
   auto [TT, Features] = getFirstFileTripleAndFeatures();
+  if (TripleName != "") {
+    TT = Triple(Triple::normalize(TripleName));
+    std::string ErrorStr;
+    if (!TargetRegistry::lookupTarget("", TT, ErrorStr))
+      ExitOnErr(make_error<StringError>("Error accessing target '" +
+                                            TripleName + "': " + ErrorStr,
+                                        inconvertibleErrorCode()));
+  }
+
   ExitOnErr(sanitizeArguments(TT, argv[0]));
 
   auto S = ExitOnErr(Session::Create(std::move(TT), std::move(Features)));
 
   enableStatistics(*S, !OrcRuntime.empty());
 
   {
     TimeRegion TR(Timers ? &Timers->LoadObjectsTimer : nullptr);