Question

39. Rewrite the following C code segment in x86 (assume bs kebx) x86 switch (b) case 1 case 2: case 3: default: return Walpha" return "beta" return gamma" return "delta" 40. Does the following function definition qualfy as a leaf function? Why or why not? int quadratic(int x, int a, int b, int c) return a square (x) b 41. Assuming the GCC calling conventions are being used, what instructions always start the prolog of a function? 42. Assuming the GCC calling conventions are being used, what instructions always end the proleg of a function? plog

Answer 1

Ans 40 : The definition of leaf function is a function that does not call other functions inside. The given function is calling square. So, This is not an example of leaf function.

Answer 2

39: Rewritten code in assembly X86 system language where b=%rbx:

SWITCH, b
CASE1
STATUS, X ; If the case1 is true, then it will return 'alpha' which is TEST1
TEST1
CASE2^CASE1
STATUS, X ; If the case2 is true, then it will return 'beta' which is TEST2
TEST2
CASE3^CASE2
STATUS, X ; If the case3 is true, then it will return 'gamma' which is TEST3
TEST3
CASE1^CASE3
TEST4           ; If none of the above is true, then it will return 'delta' which is TEST4

40. The following function does not qualify as a leaf function:

int quadratic(int x, int a, int b, int c)

{

return a*square(x)+b*x+c;

}

A leaf function is a function which can not call any other function because it’s the last set of operations of an already predefined function. Think of it like a binary tree, all the bottom nodes where no branches are expanded anymore, are the leaf functions.

The above function could be a leaf function if it hadn’t called any function itself, like square(x), which is calling a function square() to get a squared value of a variable. Hence, the function could not be considered as a leaf function.

41. When the GCC calling conventions are being used, the program contains three part of the function, one is the function prolog, body of a function and in the end, epilog of a function.

Function prolog is starting from all the variable declaration to all the meaningful operations in a function. Variable declaration is the very first statement which starts the prolog of a function.

42. When the GCC calling conventions are being used, the program contains three part of the function, one is the function prolog, body of a function and in the end, epilog of a function.

Function epilog is the process of returning the value of the variable to the Calle prior to ending the function. Usually, print statement or return statement initiates the epilog of a function to clear the memory of the stack prior to ending the program after all the calculations that are being done in the function and the resulted output is being send to the Calle variable.