Fix crash on parsing gdb remote packets

[cbook]

Summary

Prevent negative chars from being sign-extended into isprint and isspace which take and int and crash if the int is negative.

[jasonmolenda]

This looks good, the documentation for isprint() say that the value of the argument must be representable as an unsigned char, or EOF.

[cbook]

Thanks Jason. I don't have commit access. Would you or someone else be able to commit this?

[jasonmolenda]

Sending source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp
Transmitting file data .done
Committing transaction...
Committed revision 311207.

[clayborg]

We need a test for this to ensure we don't regress.

source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp

if (content_length == std::string::npos) {
         if (!m_history.DidDumpToLog())
           m_history.Dump(log);
 
         bool binary = false;
         // Only detect binary for packets that start with a '$' and have a '#CC'
         // checksum
         if (m_bytes[0] == '$' && total_length > 4) {
           for (size_t i = 0; !binary && i < total_length; ++i) {
-            if (isprint(m_bytes[i]) == 0 && isspace(m_bytes[i]) == 0) {
+            unsigned char c = m_bytes[i];
+            if (isprint(c) == 0 && isspace(c) == 0) {
               binary = true;
             }
           }
         }
         if (binary) {
           StreamString strm;
           // Packet header...
           if (CompressionIsEnabled())