[LLDB][MIPS] Handle false positives for MIPS hardware watchpoints

[mohit.bhakkad]

source/Target/StopInfo.cpp

840

Sorry, I missed else part here.
it will make m_should_stop = false

[clayborg]

Can we clean up the value in lldb-server prior to sending it up to the debugger so that the debugger doesn't have to worry about architecture specific bits in Watchpoint.cpp? That would be a better way to fix this.

source/Breakpoint/Watchpoint.cpp

158–172

Can this not be done anywhere before it gets to this point? Like maybe down in lldb-server when it is reporting the watchpoint hit? Then this can be done with "#if define(MIPS)" since lldb-server is compiled for each architecture natively.

source/Target/StopInfo.cpp

840

Add

else
{
    m_should_stop = false;
}

[mohit.bhakkad]

Resolved by rL244864

source/Breakpoint/Watchpoint.cpp

if (!m_type.IsValid())
         // Don't know how to report new & old values, since we couldn't make a scalar type for this watchpoint.
         // This works around an assert in ValueObjectMemory::Create.
         // FIXME: This should not happen, but if it does in some case we care about,
         // we can go grab the value raw and print it as unsigned.
         return false;
     }
     m_new_value_sp = ValueObjectMemory::Create (exe_ctx.GetBestExecutionContextScope(), watch_name.AsCString(), watch_address, m_type);
     m_new_value_sp = m_new_value_sp->CreateConstantValue(watch_name);
+
+    // In MIPS while storing the address of watchpoint, last 3 bits are anded with watch flags,so its possible 
+    // to get a false positive from processor for a variable with same address that of watched variable except
+    // last 3 bits. So to check such false positive we check if value of watched variable is actually changed.
+    // For now mips-lldb supports hardware watches with 'write' type only. 
+    if (m_target.GetArchitecture().GetMachine() == llvm::Triple::mips ||
+        m_target.GetArchitecture().GetMachine() == llvm::Triple::mipsel ||
+        m_target.GetArchitecture().GetMachine() == llvm::Triple::mips64 ||
+        m_target.GetArchitecture().GetMachine() == llvm::Triple::mips64el)
+    {
+        if (m_old_value_sp)
+        {
+            if (m_old_value_sp->GetValueAsSigned(NULL,NULL) == m_new_value_sp->GetValueAsSigned(NULL,NULL))
+                return false;
+        }
+    }
+
     if (m_new_value_sp && m_new_value_sp->GetError().Success())
         return true;
     else
         return false;
 }
 
 void
 Watchpoint::IncrementFalseAlarmsAndReviseHitCount()

source/Target/StopInfo.cpp

PerformAction (Event *event_ptr)
                     {
                         // We have been vetoed by the callback mechanism.
                         m_should_stop = false;
                     }
                 }
                 // Finally, if we are going to stop, print out the new & old values:
                 if (m_should_stop)
                 {
-                    wp_sp->CaptureWatchedValue(exe_ctx);
-                    
+                    if(wp_sp->CaptureWatchedValue(exe_ctx))
+                    {
                         Debugger &debugger = exe_ctx.GetTargetRef().GetDebugger();
                         StreamSP output_sp = debugger.GetAsyncOutputStream ();
                         wp_sp->DumpSnapshots(output_sp.get());
                         output_sp->EOL();
                         output_sp->Flush();
                     }
+                }
                 
             }
             else
             {
                 Log * log_process(lldb_private::GetLogIfAllCategoriesSet (LIBLLDB_LOG_PROCESS));
 
                 if (log_process)
                     log_process->Printf ("Process::%s could not find watchpoint id: %" PRId64 "...", __FUNCTION__, m_value);