Write jit profile for debugging when not jumpstarting

Summary: When we get a crash on a host that doesn't jumpstart it would still be valuable to be able to extract a JIT profile to reconstruct the crashing translations. This diff adds a new runtime option (Eval.JitSerializeDebugLocation) to indicate where this extra profile should be written, and changes the serializer to also map in any serialized profiles when not in deserializing mode.

Reviewed By: jano

Differential Revision: D76632659

fbshipit-source-id: 8a70295e999fdadde75b753e1889291eec9bb974

Author: paulbiss

hphp/doc/configs.specification

@@ -1827,6 +1827,12 @@ The format can be found in hphp/tools/configs/generate_configs.rs
   translations will be logged, and run_key column will be logged with
   the value of this option.
 
+- std::string Jit.SerializeDebugLocation = "/tmp/debugprof.jit", paulbiss
+
+  If jit profiles are disabled write serialized JIT data to disk for use in the
+  event of a crash. While crashing HHVM will map this file into memory so that
+  it may be retrieved from the core.
+
 - bool Jit.ProfileGuardTypes = false, UNKNOWN
 - uint32_t Jit.FilterLease = 1, UNKNOWN
 

hphp/runtime/vm/jit/mcgen-translate.cpp

@@ -311,6 +311,29 @@ bool serializeProfDataAndLog() {
   return serializeOptProfEnabled() && Cfg::Jit::SerializeOptProfRestart;
 }
 
+void debugDumpProfDataAndLog() {
+  auto const serverMode = Cfg::Server::Mode;
+
+  if (Cfg::Jit::SerializeDebugLocation.empty()) return;
+
+  if (serverMode) {
+    Logger::Info("retranslateAll: serializing profile data for debugging");
+  }
+
+  std::string errMsg;
+  VMWorker([&errMsg] () {
+    errMsg = serializeProfData(Cfg::Jit::SerializeDebugLocation);
+  }).run();
+
+  if (serverMode) {
+    if (errMsg.empty()) {
+      Logger::Info("retranslateAll: serializing done");
+    } else {
+      Logger::FError("serializeProfData failed with: {}", errMsg);
+    }
+  }
+}
+
 /*
  * Schedule serialization of optimized code's profile to happen in the future.
  */
@@ -410,6 +433,10 @@ void retranslateAll(bool skipSerialize) {
   //    serialization of optimized code's profile is also enabled.
 
   if (serialize && !skipSerialize && serializeProfDataAndLog()) return;
+  if (!skipSerialize && !isJitSerializing() && !isJitDeserializing() &&
+      Cfg::Repo::Authoritative) {
+    debugDumpProfDataAndLog();
+  }
 
   // 5) Generate machine code for all the profiled functions.
 

hphp/runtime/vm/jit/prof-data-serialize.cpp

@@ -869,7 +869,9 @@ rds::Ordering::Item read_rds_ordering_item(ProfDataDeserializer& des) {
 
 void write_rds_ordering(ProfDataSerializer& ser) {
   rds::Ordering order;
-  if (Cfg::Eval::ReorderRDS) order = rds::profiledOrdering();
+  if (Cfg::Eval::ReorderRDS && isJitSerializing()) {
+    order = rds::profiledOrdering();
+  }
   write_container(ser, order.persistent, write_rds_ordering_item);
   write_container(ser, order.local, write_rds_ordering_item);
   write_container(ser, order.normal, write_rds_ordering_item);
@@ -2209,6 +2211,10 @@ std::string serializeProfData(const std::string& filename) {
       s_lastMappers = std::move(ser.getMappers());
     }
 
+    // If we crash we can recover the current TC state using the profile we just
+    // serialized so ensure it gets mapped back into the core.
+    s_deserializedFile = filename;
+
     return "";
   } catch (std::runtime_error& err) {
     return folly::sformat("Failed to serialize profile data: {}", err.what());