Fix bug with register values byte order in expression evaluation

[mamai]

Summary

The evaluation of expressions containing register values was broken for targets for which endianness differs from host.

This patch fixes issues like:
(lldb) reg read pc

pc = 0x00400020  arithmetic.elf`main + 32 at main.c:12

(lldb) expr -f hex -- $pc
(unsigned int) $2 = 0x20004000

Where the second command will now give the right value (0x00400020).

[clayborg]

I will defer to Sean Callanan.

[spyffe]

Looks fine to me, but let's put in an assertion to make sure our assumptions in making this change are not violated.

source/Expression/Materializer.cpp

1282

Let's put an lldbassert in here to make sure scalar.GetByteSize() == register_data.GetByteSize().
I know it ought to be, but I'm a little bit wary of that code.

[mamai]

I have updated the patch to add the assertion.

[mamai]

Are the changes correct? And if so, could someone commit it for me? I don't have commit access.

[ADodds]

I am happy to commit this for you since you have addressed the concerns raised by Sean.

source/Expression/Materializer.cpp

void Materialize(lldb::StackFrameSP &frame_sp,
         {
             err.SetErrorStringWithFormat("data for register %s had size %llu but we expected %llu", m_register_info.name, (unsigned long long)register_data.GetByteSize(), (unsigned long long)m_register_info.byte_size);
             return;
         }
         
         m_register_contents.reset(new DataBufferHeap(register_data.GetDataStart(), register_data.GetByteSize()));
         
         Error write_error;
-        
-        map.WriteMemory(load_addr, register_data.GetDataStart(), register_data.GetByteSize(), write_error);
-        
+        Scalar scalar;
+        reg_value.GetScalarValue(scalar);
+
+        map.WriteScalarToMemory(load_addr, scalar, scalar.GetByteSize(), write_error);
         if (!write_error.Success())
         {
             err.SetErrorStringWithFormat("couldn't write the contents of register %s: %s", m_register_info.name, write_error.AsCString());
             return;
         }
     }
     
     void Dematerialize(lldb::StackFrameSP &frame_sp,