Thread context should always contain FP regisers

RTX only stacks the floating point registers when it detects that a
thread makes use of them. Previously ThreadMRI would only return the
FP registers in the context if the thread had them but GDB will
actually return an error if it sees the size of the context change
between debug halts. This commit will return a dummy set of zeroed out
float registers to GDB when the RTX thread doesn't have any of its own
to return.

Author: adamgreen

libraries/ThreadMRI/src/ThreadMRI.cpp

@@ -120,7 +120,10 @@ void                            (*g_origSerialISR)(void);
     #define CONTEXT_ENTRIES     5
 #endif
 
-static ScatterGatherEntry   g_contextEntries[CONTEXT_ENTRIES];
+static ScatterGatherEntry       g_contextEntries[CONTEXT_ENTRIES];
+
+// Floats to be returned in context if the thread being debugged hsa no stored float state.
+static uint32_t                 g_tempFloats[33];
 
 // UNDONE: For debugging. If different than g_haltedThreadId then the mriMain() thread was signalled when the previous
 //         instance was still running.
@@ -331,6 +334,15 @@ static void readThreadContext(osThreadId_t thread)
         // FPSCR
         g_contextEntries[7].pValues = pThreadContext + 48;
         g_contextEntries[7].count = 1;
+    } else {
+        memset(g_tempFloats, 0, sizeof(g_tempFloats));
+        // S0-S31, FPSCR
+        g_contextEntries[5].pValues = g_tempFloats;
+        g_contextEntries[5].count = 33;
+        g_contextEntries[6].pValues = NULL;
+        g_contextEntries[6].count = 0;
+        g_contextEntries[7].pValues = NULL;
+        g_contextEntries[7].count = 0;
     }
 }