Bug in LLDB RSP client causes '$O' packets to be decoded incorrectly

[evgeny777]

Summary

Character with ASCII code 0 is incorrectly treated by LLDB as the end of RSP packet. The left of the debugger server output is silently ignored.

[clayborg]

Why did we introduce StringExtractor::GetHexU8Ex() if the only place that calls it is StringExtractor::GetHexU8() and other places that should just call StringExtractor::GetHexU8()? Seems like you should just fix StringExtractor::GetHexU8() to contain the contents of StringExtractor::GetHexU8Ex() and get rid of StringExtractor::GetHexU8Ex().

[evgeny777]

GetHexU8Ex is called from SendContinuePacketAndWaitForResponse() in GDBRemoteCommunicationClient.cpp. Please take a look at the patch

[clayborg]

Ah yes, just the fail_value is the difference.

[evgeny777]

Thanks. Could you please commit my changes, as I do not have write access

[dawn]

Thanks for the patch, I will commit it.

lldb/trunk/include/lldb/Utility/StringExtractor.h

public:
 
     int
     DecodeHexU8();
 
     uint8_t
     GetHexU8 (uint8_t fail_value = 0, bool set_eof_on_fail = true);
 
     bool
+    GetHexU8Ex (uint8_t& ch, bool set_eof_on_fail = true);
+
+    bool
     GetNameColonValue (std::string &name, std::string &value);
 
     int32_t
     GetS32 (int32_t fail_value, int base = 0);
 
     uint32_t
     GetU32 (uint32_t fail_value, int base = 0);
 

lldb/trunk/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.cpp

while (state == eStateRunning)
                     break;
 
                 case 'O':
                     // STDOUT
                     {
                         got_async_packet = true;
                         std::string inferior_stdout;
                         inferior_stdout.reserve(response.GetBytesLeft () / 2);
-                        char ch;
-                        while ((ch = response.GetHexU8()) != '\0')
-                            inferior_stdout.append(1, ch);
+
+                        uint8_t ch;
+                        while (response.GetHexU8Ex(ch))
+                        {
+                            if (ch != 0)
+                                inferior_stdout.append(1, (char)ch);
+                        }
                         process->AppendSTDOUT (inferior_stdout.c_str(), inferior_stdout.size());
                     }
                     break;
 
                 case 'A':
                     // Async miscellaneous reply. Right now, only profile data is coming through this channel.
                     {
                         got_async_packet = true;

lldb/trunk/source/Utility/StringExtractor.cpp

 
 //----------------------------------------------------------------------
 // Extract an unsigned character from two hex ASCII chars in the packet
 // string
 //----------------------------------------------------------------------
 uint8_t
 StringExtractor::GetHexU8 (uint8_t fail_value, bool set_eof_on_fail)
 {
+    GetHexU8Ex(fail_value, set_eof_on_fail);
+    return fail_value;
+}
+
+bool
+StringExtractor::GetHexU8Ex (uint8_t& ch, bool set_eof_on_fail)
+{
     int byte = DecodeHexU8();
     if (byte == -1)
     {
         if (set_eof_on_fail || m_index >= m_packet.size())
             m_index = UINT64_MAX;
-        return fail_value;
+        // ch should not be changed in case of failure
+        return false;
     }
-    return (uint8_t)byte;
+    ch = (uint8_t)byte;
+    return true;
 }
 
 uint32_t
 StringExtractor::GetU32 (uint32_t fail_value, int base)
 {
     if (m_index < m_packet.size())
     {
         char *end = nullptr;