Reduced packet counts to the remote GDB server where possible.

We have been working on reducing the packet count that is sent between LLDB and the debugserver on MacOSX and iOS. Our approach to this was to reduce the packets required when debugging multiple threads. We currently make one qThreadStopInfoXXXX call (where XXXX is the thread ID in hex) per thread except the thread that stopped with a stop reply packet. In order to implement multiple thread infos in a single reply, we need to use structured data, which means JSON. The new jThreadsInfo packet will attempt to retrieve all thread infos in a single packet. The data is very similar to the stop reply packets, but packaged in JSON and uses JSON arrays where applicable. The JSON output looks like:


[
  { "tid":1580681,
    "metype":6,
    "medata":[2,0],
    "reason":"exception",
    "qaddr":140735118423168,
    "registers": {
      "0":"8000000000000000",
      "1":"0000000000000000",
      "2":"20fabf5fff7f0000",
      "3":"e8f8bf5fff7f0000",
      "4":"0100000000000000",
      "5":"d8f8bf5fff7f0000",
      "6":"b0f8bf5fff7f0000",
      "7":"20f4bf5fff7f0000",
      "8":"8000000000000000",
      "9":"61a8db78a61500db",
      "10":"3200000000000000",
      "11":"4602000000000000",
      "12":"0000000000000000",
      "13":"0000000000000000",
      "14":"0000000000000000",
      "15":"0000000000000000",
      "16":"960b000001000000",
      "17":"0202000000000000",
      "18":"2b00000000000000",
      "19":"0000000000000000",
      "20":"0000000000000000"},
    "memory":[
      {"address":140734799804592,"bytes":"c8f8bf5fff7f0000c9a59e8cff7f0000"},
      {"address":140734799804616,"bytes":"00000000000000000100000000000000"}
    ]
  }
]

It contains an array of dicitionaries with all of the key value pairs that are normally in the stop reply packet. Including the expedited registers. Notice that is also contains expedited memory in the "memory" key. Any values in this memory will get included in a new L1 cache in lldb_private::Process where if a memory read request is made and that memory request fits into one of the L1 memory cache blocks, it will use that memory data. If a memory request fails in the L1 cache, it will fall back to the L2 cache which is the same block sized caching we were using before these changes. This allows a process to expedite memory that you are likely to use and it reduces packet count. On MacOSX with debugserver, we expedite the frame pointer backchain for a thread (up to 256 entries) by reading 2 pointers worth of bytes at the frame pointer (for the previous FP and PC), and follow the backchain. Most backtraces on MacOSX and iOS now don't require us to read any memory!

We will try these packets out and if successful, we should port these to lldb-server in the near future. 

<rdar://problem/21494354>

llvm-svn: 240354

1 files changed, 17 insertions, 0 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h
index 02f449ffca4..29ca17ef9cb 100644
--- a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h
+++ b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.h
@@ -323,6 +323,9 @@ protected:
     void
     GetMaxMemorySize();
 
+    bool
+    CalculateThreadStopInfo (ThreadGDBRemote *thread);
+
     //------------------------------------------------------------------
     /// Broadcaster event bits definitions.
     //------------------------------------------------------------------
@@ -346,6 +349,7 @@ protected:
     typedef std::vector< std::pair<lldb::tid_t,int> > tid_sig_collection;
     typedef std::map<lldb::addr_t, lldb::addr_t> MMapMap;
     tid_collection m_thread_ids; // Thread IDs for all threads. This list gets updated after stopping
+    StructuredData::ObjectSP m_threads_info_sp; // Stop info for all threads if "jThreadsInfo" packet is supported
     tid_collection m_continue_c_tids;                  // 'c' for continue
     tid_sig_collection m_continue_C_tids; // 'C' for continue with signal
     tid_collection m_continue_s_tids;                  // 's' for step
@@ -379,6 +383,19 @@ protected:
     lldb::StateType
     SetThreadStopInfo (StringExtractor& stop_packet);
 
+    lldb::StateType
+    SetThreadStopInfo (StructuredData::Dictionary *thread_dict);
+
+    lldb::ThreadSP
+    SetThreadStopInfo (lldb::tid_t tid,
+                       uint8_t signo,
+                       const std::string &thread_name,
+                       const std::string &reason,
+                       const std::string &description,
+                       uint32_t exc_type,
+                       const std::vector<lldb::addr_t> &exc_data,
+                       lldb::addr_t thread_dispatch_qaddr);
+
     void
     HandleStopReplySequence ();