[trace][intelpt] Support system-wide tracing [15] - Make triple optional

[wallace]

Summary

The process triple should only be needed when LLDB can't identify the correct
triple on its own. Examples could be universal mach-o binaries. But in any case,
at least for most of ELF files, LLDB should be able to do the job without having
the user specify the triple manually.

lldb/source/Plugins/Trace/intel-pt/TraceIntelPTJSONStructs.h

 
 struct JSONThread {
   int64_t tid;
   llvm::Optional<std::string> trace_buffer;
 };
 
 struct JSONProcess {
   int64_t pid;
-  std::string triple;
+  llvm::Optional<std::string> triple;
   std::vector<JSONThread> threads;
   std::vector<JSONModule> modules;
 };
 
 struct JSONCore {
   lldb::core_id_t core_id;
   std::string trace_buffer;
   std::string context_switch_trace;

lldb/source/Plugins/Trace/intel-pt/TraceIntelPTSessionFileParser.cpp

TraceIntelPTSessionFileParser::ParseThread(ProcessSP &process_sp,
   process_sp->GetThreadList().AddThread(thread_sp);
   return thread_sp;
 }
 
 Expected<TraceIntelPTSessionFileParser::ParsedProcess>
 TraceIntelPTSessionFileParser::ParseProcess(const JSONProcess &process) {
   TargetSP target_sp;
   Status error = m_debugger.GetTargetList().CreateTarget(
-      m_debugger, /*user_exe_path*/ StringRef(), process.triple,
+      m_debugger, /*user_exe_path*/ StringRef(), process.triple.getValueOr(""),
       eLoadDependentsNo,
       /*platform_options*/ nullptr, target_sp);
 
   if (!target_sp)
     return error.ToError();
 
   ParsedProcess parsed_process;
   parsed_process.target_sp = target_sp;
"cpuInfo": {
     "vendor": "GenuineIntel" | "unknown",
     "family": integer,
     "model": integer,
     "stepping": integer
   },
   "processes": [
     {
       "pid": integer,
-      "triple": string,
-          // clang/llvm target triple.
+      "triple"?: string,
+          // Optional clang/llvm target triple.
       "threads": [
         {
           "tid": integer,
           "traceBuffer"?: string
               // Path to the raw Intel PT buffer file for this thread.
         }
       ],
       "modules": [

lldb/test/API/commands/trace/TestTraceLoad.py

"cpuInfo": {
     // CPU information gotten from, for example, /proc/cpuinfo.
 
     "vendor": "GenuineIntel" | "unknown",
     "family": integer,
     "model": integer,
     "stepping": integer
   },'''])
 
-        # Now we test a missing field in the global session file
+        # Now we test a wrong cpu family field in the global session file
         self.expect("trace load -v " + os.path.join(src_dir, "intelpt-trace", "trace_bad2.json"), error=True,
-            substrs=['error: missing value at traceSession.processes[1].triple', "Context", "Schema"])
+            substrs=['error: expected uint64_t at traceSession.cpuInfo.family', "Context", "Schema"])
 
         # Now we test a missing field in the intel-pt settings
         self.expect("trace load -v " + os.path.join(src_dir, "intelpt-trace", "trace_bad4.json"), error=True,
             substrs=['''error: missing value at traceSession.cpuInfo.family
 
 Context:
 {
   "cpuInfo": /* error: missing value */ {

lldb/test/API/commands/trace/intelpt-multi-core-trace/trace.json

"processes": [
           "tid": 3497234
         },
         {
           "tid": 3497496
         },
         {
           "tid": 3497497
         }
-      ],
-      "triple": "x86_64-unknown-linux-gnu"
+      ]
     }
   ],
   "tscPerfZeroConversion": {
     "timeMult": 1076264588,
     "timeShift": 31,
     "timeZero": 18433473881008870804
   },
   "type": "intel-pt"
 }

lldb/test/API/commands/trace/intelpt-trace/trace_bad2.json

 {
   "type": "intel-pt",
   "cpuInfo": {
     "vendor": "GenuineIntel",
-    "family": 6,
+    "family": "123",
     "model": 79,
     "stepping": 1
   },
   "processes": [
     {
       "pid": 1234,
-      "triple": "x86_64-*-linux",
       "threads": [
         {
           "tid": 5678,
           "traceBuffer": "3842849.trace"
         }
       ],
       "modules": [
         {