This is assembly language code. I deleted all the assembler directives. Please d

Question

This is assembly language code. I deleted all the assembler directives. Please describe the result of each instruction in the code below please.

main:

pushq %rbp

movq %rsp, %rbp

subq $16, %rsp

movl $5, -12(%rbp)

movl $3, -8(%rbp)

movl -12(%rbp), %edx

movl -8(%rbp), %eax

addl %edx, %eax

movl %eax, %edx

shrl $31, %edx

addl %edx, %eax

sarl %eax

movl %eax, -4(%rbp)

leaq .LC0(%rip), %rsi

leaq _ZSt4cout(%rip), %rdi

call _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc@PLT

movq %rax, %rdx

movl -4(%rbp), %eax

movl %eax, %esi

movq %rdx, %rdi

call _ZNSolsEi@PLT

movq %rax, %rdx

movq _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_@GOTPCREL(%rip), %rax

movq %rax, %rsi

movq %rdx, %rdi

call _ZNSolsEPFRSoS_E@PLT

movl $0, %eax

leave

ret

_Z41__static_initialization_and_destruction_0ii:

pushq %rbp

movq %rsp, %rbp

subq $16, %rsp

movl %edi, -4(%rbp)

movl %esi, -8(%rbp)

cmpl $1, -4(%rbp)

jne .L5

cmpl $65535, -8(%rbp)

jne .L5

leaq _ZStL8__ioinit(%rip), %rdi

call _ZNSt8ios_base4InitC1Ev@PLT

leaq __dso_handle(%rip), %rdx

leaq _ZStL8__ioinit(%rip), %rsi

movq _ZNSt8ios_base4InitD1Ev@GOTPCREL(%rip), %rax

movq %rax, %rdi

call __cxa_atexit@PLT

nop

leave

ret

_GLOBAL__sub_I_main:

pushq %rbp

movq %rsp, %rbp

movl $65535, %esi

movl $1, %edi

call _Z41__static_initialization_and_destruction_0ii

popq %rbp

ret

the c++ code that this assembly language was generated by is listed below:

#include

#define Y 3

int main()

{

int x = 5;

int y = Y;

int ave = (x + y) / 2;

std::cout << "Average is " << ave << std::endl;

return 0;

}

Explanation / Answer

main:

pushq %rbp # we push the old base pointer onto the stack to save it for later. Then we copy the value of the base pointer

movq %rsp, %rbp # %rbp points to the base of the main's stack frame

subq $16, %rsp # unsued stack in the stack structure

movl $5, -12(%rbp) # move 5 into rbp // local variables //int x

movl $3, -8(%rbp) # move 3 into rbp // local variables // Y

movl -12(%rbp), %edx # move the variable value into another variable

movl -8(%rbp), %eax # move the variable value into another variable

addl %edx, %eax # adding a variable

movl %eax, %edx # move the variable value into another variable

shrl $31, %edx

addl %edx, %eax # update the stack structure with the return address

sarl %eax

movl %eax, -4(%rbp) # moving the value from one register to another register

leaq .LC0(%rip), %rsi # links to the header file to call the cout function

leaq _ZSt4cout(%rip), %rdi # calls the function cout

call _ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc@PLT

movq %rax, %rdx #the rest 4 lines to get the value given in the cout

movl -4(%rbp), %eax

movl %eax, %esi

movq %rdx, %rdi

call _ZNSolsEi@PLT # calling it from the stack

movq %rax, %rdx

movq _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_@GOTPCREL(%rip), %rax

movq %rax, %rsi

movq %rdx, %rdi

call _ZNSolsEPFRSoS_E@PLT #calling the variable avg

movl $0, %eax

leave # leaving the function

ret # return address stored in the stack

_Z41__static_initialization_and_destruction_0ii:

pushq %rbp

movq %rsp, %rbp

subq $16, %rsp

movl %edi, -4(%rbp)

movl %esi, -8(%rbp)

cmpl $1, -4(%rbp)

jne .L5 # rest all to initilize the iostream in the file

cmpl $65535, -8(%rbp)

jne .L5

leaq _ZStL8__ioinit(%rip), %rdi

call _ZNSt8ios_base4InitC1Ev@PLT

leaq __dso_handle(%rip), %rdx

leaq _ZStL8__ioinit(%rip), %rsi

movq _ZNSt8ios_base4InitD1Ev@GOTPCREL(%rip), %rax

movq %rax, %rdi

call __cxa_atexit@PLT

nop

leave #leaves the function

ret # function is set to return

_GLOBAL__sub_I_main: # main function starts from here

pushq %rbp # pusing the value in the stack as base address

movq %rsp, %rbp # referencing it in the base address in the stack

movl $65535, %esi # variable loading in the stack

movl $1, %edi # return is set to 1

call _Z41__static_initialization_and_destruction_0ii # calling the printf function

popq %rbp # printing the ave in the program

ret # returning 1

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