An integer overflow occurs when an arithmetic operation on integers produces a result that is too large to be represented within the range of values that can be stored in the data type of the integers being used. This can cause unexpected and potentially malicious behavior in a program, such as allowing an attacker to bypass security checks or causing a crash.
In the ARM architecture, integer overflows can occur in various arithmetic operations, such as addition, subtraction, multiplication, and division. To prevent integer overflows, it is important to use proper data types and to check for overflow conditions before performing arithmetic operations. For example, you can use the adds or adc (add with carry) instruction to perform an addition and check the carry flag to see if an overflow occurred. Similarly, you can use the subs or sbc (subtract with carry) instruction to perform a subtraction and check the carry flag to see if an underflow occurred.
It is also possible to use libraries or compiler-provided built-in functions to perform arithmetic operations that automatically check for and handle integer overflows. For example, in C, you can use the __builtin_add_overflow() function to perform an addition and check for an overflow, or you can use the __builtin_saturate_add() function to perform an addition that automatically saturates to the maximum or minimum representable value in case of an overflow.
Example:
In this example, the value in register r0 is initialized to the maximum positive value that can be represented by a 32-bit integer (0x7fffffff). The add instruction then adds 1 to this value, which causes an integer overflow because the result (2147483648) is too large to be represented by a 32-bit integer. The program enters an infinite loop because the b (branch) instruction jumps to the current location (.) indefinitely.
To prevent this integer overflow, you can use the adds or adc instruction to perform the addition and check the carry flag to see if an overflow occurred.
The adds instruction performs the addition and sets the carry flag (C) if an overflow occurred. The bcs (branch if carry set) instruction tests the carry flag and jumps to the current location if it is set, causing the program to enter an infinite loop if an overflow occurred. If the carry flag is not set (i.e., no overflow occurred), the program continues to the next instruction.