This problem will give you a chance to reverse engineer a switch statement from

Question

This problem will give you a chance to reverse engineer a switch statement from machine code. In the following procedure, the body of the switch statement has been removed:

The disassembled machine code for the procedure is shown below. Recall parameter x is passed in register %rdi and parameter n is passed in register %rsi. The jump table resides in a different area of memory. We can see from the mov at address 0x040065e that the jump table begins at address 0x0400798. Using the gdb debugger, we can examine the ten 8-byte words of memory comprising the jump table with the command x/10x 0x400798. gdb prints the following:

Explanation / Answer

long switch_prob(long x, long n)

{

long result = n;

switch(x){

case 60: result = n*8; break;

case 62: result = n*8; break;

case 63: result = n;

result >>= 0x3;

break;

case 64: result = n;

result <<= 0x4;

result -= n;

n = result;

n *= n;

result = n + 75;

break;

case 65: n *= n;

result = n + 75;

break;

default: result = n + 75;

}

return result;

}

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