Ollydbg : sign extending with Movsx

Question

Movsx sign-extends a register with 1 right?

So why in Ollydbg i got this :

• Before:
• After:

I should have FFFFFF65 instead of 00000065 in ECX no?

Thank you !

Answer 1

The byte at the memory location has the value 65h. This is a positive number and thus the extension will fill the 3 highest bytes of ECX with zero giving 00000065h .