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angr / angr-platforms

A collection of extensions to angr to handle new platforms
http://angr.io/
BSD 2-Clause "Simplified" License
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Fix overflow flag for MSP430 SUB(C) instruction #27

Closed hidde-jan closed 5 years ago

hidde-jan commented 5 years ago

From https://sites.google.com/site/arch1utep/home/course_outline/arithmetic_flags:

SUB(.B),SUBC(.B),CMP(.B) 
V=1 when the result of
    Positive – Negative is a  Negative 
    Negative – Positive is a Positive [...] 
V=0 othewise

So dst and res should not have the same sign and dst and src should also not have the same sign (i.e. src and ret should have the same sign.

From wikipedia:

The overflow flag is thus set when the most significant bit (here considered the sign bit) is changed by adding two numbers with the same sign (or subtracting two numbers with opposite signs). Overflow never occurs when the sign of two addition operands are different (or the sign of two subtraction operands are the same).