Practical Reverse Engineering p. 79 #5

Question number 5 on page 79 of Practical Reverse Engineering is as follows:

Figure 2-11 is simple as well. The actual string names have been removed so you cannot cheat by searching the Internet.

Here is the disassembly of the function:

Figure 2-11. Practical Reverse Engineering. © 2014 by Bruce Dang

The ARM processor is in Thumb state. This function can be written as a switch statement. It essentially takes an enum and returns a string based on the value.

const char *get_string(DWORD string_enum)
{
    /* MOV R3, R0 */
    switch (string_enum)
    {
        case 6:             /* CMP R3, #6 */
            return "E";     /* LDR R0, =aE ; "E" */

        case 7:             /* CMP R3, #7 */
            return "D";     /* LDR R0, =aD ; "D" */

        case 8:             /* CMP R3, #8 */
            return "C";     /* LDR R0, =ac ; "C" */

        case 9:             /* CMP R3, #9 */
            return "B";     /* LDR R0, =aB ; "B" */

        default:
            return "A";     /* LDR R0, =aA ; "A" */ 
    }
}