Implement the "qSymbol" packet in order to be able to read queue information in debugserver and return the info in the stop reply packets.

A "qSymbol::" is sent when shared libraries have been loaded by hooking into the Process::ModulesDidLoad() function from within ProcessGDBRemote. This function was made virtual so that the ProcessGDBRemote version is called, which then first calls the Process::ModulesDidLoad(), and then it queries for any symbol lookups that the remote GDB server might want to do.

This allows debugserver to request the "dispatch_queue_offsets" symbol so that it can read the queue name, queue kind and queue serial number and include this data as part of the stop reply packet. Previously each thread would have to do 3 memory reads in order to read the queue name.

This is part of reducing the number of packets that are sent between LLDB and the remote GDB server.

<rdar://problem/21494354>

llvm-svn: 240466

1 files changed, 87 insertions, 0 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
index fe88de4c866..f487ae94192 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp
@@ -33,6 +33,7 @@
 #include "lldb/Host/HostInfo.h"
 #include "lldb/Host/StringConvert.h"
 #include "lldb/Host/TimeValue.h"
+#include "lldb/Symbol/Symbol.h"
 #include "lldb/Target/Target.h"
 #include "lldb/Target/MemoryRegionInfo.h"
 #include "lldb/Target/UnixSignals.h"
@@ -98,6 +99,7 @@ GDBRemoteCommunicationClient::GDBRemoteCommunicationClient() :
     m_supports_z4 (true),
     m_supports_QEnvironment (true),
     m_supports_QEnvironmentHexEncoded (true),
+    m_supports_qSymbol (true),
     m_curr_pid (LLDB_INVALID_PROCESS_ID),
     m_curr_tid (LLDB_INVALID_THREAD_ID),
     m_curr_tid_run (LLDB_INVALID_THREAD_ID),
@@ -370,6 +372,7 @@ GDBRemoteCommunicationClient::ResetDiscoverableSettings()
     m_supports_z4 = true;
     m_supports_QEnvironment = true;
     m_supports_QEnvironmentHexEncoded = true;
+    m_supports_qSymbol = true;
     
     m_host_arch.Clear();
     m_process_arch.Clear();
@@ -4241,3 +4244,87 @@ GDBRemoteCommunicationClient::ReadExtFeature (const lldb_private::ConstString ob
     err.Success( );
     return true;
 }
+
+// Notify the target that gdb is prepared to serve symbol lookup requests.
+//  packet: "qSymbol::"
+//  reply:
+//  OK                  The target does not need to look up any (more) symbols.
+//  qSymbol:<sym_name>  The target requests the value of symbol sym_name (hex encoded).
+//                      LLDB may provide the value by sending another qSymbol packet
+//                      in the form of"qSymbol:<sym_value>:<sym_name>".
+
+void
+GDBRemoteCommunicationClient::ServeSymbolLookups(lldb_private::Process *process)
+{
+    if (m_supports_qSymbol)
+    {
+        Mutex::Locker locker;
+        if (GetSequenceMutex(locker, "GDBRemoteCommunicationClient::ServeSymbolLookups() failed due to not getting the sequence mutex"))
+        {
+            StreamString packet;
+            packet.PutCString ("qSymbol::");
+            while (1)
+            {
+                StringExtractorGDBRemote response;
+                if (SendPacketAndWaitForResponseNoLock(packet.GetData(), packet.GetSize(), response) == PacketResult::Success)
+                {
+                    if (response.IsOKResponse())
+                    {
+                        // We are done serving symbols requests
+                        return;
+                    }
+
+                    if (response.IsUnsupportedResponse())
+                    {
+                        // qSymbol is not supported by the current GDB server we are connected to
+                        m_supports_qSymbol = false;
+                        return;
+                    }
+                    else
+                    {
+                        llvm::StringRef response_str(response.GetStringRef());
+                        if (response_str.startswith("qSymbol:"))
+                        {
+                            response.SetFilePos(strlen("qSymbol:"));
+                            std::string symbol_name;
+                            if (response.GetHexByteString(symbol_name))
+                            {
+                                if (symbol_name.empty())
+                                    return;
+
+                                addr_t symbol_load_addr = LLDB_INVALID_ADDRESS;
+                                lldb_private::SymbolContextList sc_list;
+                                if (process->GetTarget().GetImages().FindSymbolsWithNameAndType(ConstString(symbol_name), eSymbolTypeAny, sc_list))
+                                {
+                                    SymbolContext sc;
+                                    if (sc_list.GetContextAtIndex(0, sc))
+                                    {
+                                        if (sc.symbol)
+                                            symbol_load_addr = sc.symbol->GetAddress().GetLoadAddress(&process->GetTarget());
+                                    }
+                                }
+                                // This is the normal path where our symbol lookup was successful and we want
+                                // to send a packet with the new symbol value and see if another lookup needs to be
+                                // done.
+
+                                // Change "packet" to contain the requested symbol value and name
+                                packet.Clear();
+                                packet.PutCString("qSymbol:");
+                                if (symbol_load_addr != LLDB_INVALID_ADDRESS)
+                                    packet.Printf("%" PRIx64, symbol_load_addr);
+                                packet.PutCString(":");
+                                packet.PutBytesAsRawHex8(symbol_name.data(), symbol_name.size());
+                                continue; // go back to the while loop and send "packet" and wait for another response
+                            }
+                        }
+                    }
+                }
+            }
+            // If we make it here, the symbol request packet response wasn't valid or
+            // our symbol lookup failed so we must abort
+            return;
+
+        }
+    }
+}
+