Assembly Language Programming - III

Transcription

1 Assembly Language Programming - III

2 GDB Debugger Please refer to the handout New GDB commands (power.s) info registers (prints all register values) print/d $eax (prints individual register value. Note $ ) print/d (prints value in decimal) print/c cprompt1(prints 1 st byte of mem cprompt1) x/d & (prints address and dereferenced value) x/c &cprompt1 x/s &cprompt1 2

3 Some facts Local variables consists of stack frames (activation records) Each stack frame holds some local data for a function Special registers ESP (extended stack pointer) => Top of the current stack frame EBP (extended base pointer) => Bottom of the current stack frame

4 Local variables grows toward low memory Push operation subtracts from ESP does not affect EBP Pop operation add to ESP does not affect EBP ESP EBP EBP retains its value throughout function Low High

5 Example: powerfunction.c Same basic functionality but: uses local variables calls power() function 5

6 #include <stdio.h> static int power(int, int ) { int ipower = 1; int iindex; for (iindex = 1; iindex <= ; iindex++) ipower *= ; FLATTEN IT } return ipower; int main(int argc, char *argv[]) { int ; int ; int ipower; printf("enter the base: "); scanf("%d", &); printf("enter the exponent: "); scanf("%d", &); ipower = power(, ); printf("%d to the %d power is %d.\n",,, ipower); } return 0;

7 ### ### powerfunction.s ### Author: Bob Dondero ### Functions ### section ".rodata" cprompt1:.asciz "Enter the base: " cprompt2:.asciz "Enter the exponent: " cscanfformat:.asciz cresult:.asciz "%d" "%d raised to the %d power is %d.\n"

8 ### section ".data" ### section ".bss" ###

9 ## ## int main(int argc, char *argv[]) ## Read a non-negative base and exponent from stdin. Write ## base raised to the exponent power to stdout. Return 0. ## ## Local variable offsets:.equ IBASE, -4.equ IEXP, -8.equ IPOWER, -12 aliases.globl.type main: main main,@function pushl movl %ebp %, %ebp ## int subl $4, % ## int subl $4, % ## int ipower subl $4, % FFFFFFFF 9

10 ## ## int main(int argc, char *argv[]) ## Read a non-negative base and exponent from stdin. Write ## base raised to the exponent power to stdout. Return 0. ## ## Local variable offsets:.equ IBASE, -4.equ IEXP, -8.equ IPOWER, -12.globl.type main: main main,@function pushl movl %ebp %, %ebp ## int subl $4, % ## int subl $4, % ## int ipower subl $4, % FFFFFFFF 10

11 ## ## int main(int argc, char *argv[]) ## Read a non-negative base and exponent from stdin. Write ## base raised to the exponent power to stdout. Return 0. ## ## Local variable offsets:.equ IBASE, -4.equ IEXP, -8.equ IPOWER, -12.globl.type main: main main,@function pushl movl %ebp %, %ebp ## int subl $4, % ## int subl $4, % ## int ipower subl $4, % FFFFFFFF 11

12 ## ## int main(int argc, char *argv[]) ## Read a non-negative base and exponent from stdin. Write ## base raised to the exponent power to stdout. Return 0. ## ## Local variable offsets:.equ IBASE, -4.equ IEXP, -8.equ IPOWER, -12.globl.type main: main main,@function pushl movl %ebp %, %ebp ## int subl $4, % ## int subl $4, % ## int ipower subl $4, % FFFFFFFF 12

13 ## ## int main(int argc, char *argv[]) ## Read a non-negative base and exponent from stdin. Write ## base raised to the exponent power to stdout. Return 0. ## ## Local variable offsets:.equ IBASE, -4.equ IEXP, -8.equ IPOWER, -12.globl.type main: pushl movl main main,@function %ebp %, %ebp ## int subl $4, % ## int subl $4, % ## int ipower subl $4, % FFFFFFFF 13

14 ## ## int main(int argc, char *argv[]) ## Read a non-negative base and exponent from stdin. Write ## base raised to the exponent power to stdout. Return 0. ## ## Local variable offsets:.equ IBASE, -4.equ IEXP, -8.equ IPOWER, -12.globl.type main: pushl movl main main,@function %ebp %, %ebp ipower ## int subl $4, % ## int subl $4, % ## int ipower subl $4, % FFFFFFFF 14

15 ## printf("enter the base: ") pushl $cprompt1 call printf addl $4, % ## scanf("%d", &) leal IBASE(%ebp), %eax ## Alternative to leal: ## movl %ebp,%eax ## addl $IBASE,%eax pushl %eax pushl $cscanfformat call scanf addl $8, % cpro..1 ipower 15

16 ## printf("enter the base: ") pushl $cprompt1 call printf addl $4, % ## scanf("%d", &) leal IBASE(%ebp), %eax ## Alternative to leal: ## movl %ebp,%eax ## addl $IBASE,%eax pushl %eax pushl $cscanfformat call scanf addl $8, % addl $4, % eip cpro..1 ipower 16

17 ## printf("enter the base: ") pushl $cprompt1 call printf addl $4, % ## scanf("%d", &) leal IBASE(%ebp), %eax ## Alternative to leal: ## movl %ebp,%eax ## addl $IBASE,%eax pushl %eax pushl $cscanfformat call scanf addl $8, % Xeip cpro..1 ipower 17

18 ## printf("enter the base: ") pushl $cprompt1 call printf addl $4, % ## scanf("%d", &) leal IBASE(%ebp), %eax ## Alternative to leal: ## movl %ebp,%eax ## addl $IBASE,%eax pushl %eax pushl $cscanfformat call scanf addl $8, % IBASE = -4 eax ipower 18

19 ## printf("enter the base: ") pushl $cprompt1 call printf addl $4, % ## scanf("%d", &) leal IBASE(%ebp), %eax ## Alternative to leal: ## movl %ebp,%eax ## addl $IBASE,%eax pushl %eax pushl $cscanfformat call scanf addl $8, % COPY BY REFERENCE addr ipower 19

20 ## printf("enter the base: ") pushl $cprompt1 call printf addl $4, % ## scanf("%d", &) leal IBASE(%ebp), %eax ## Alternative to leal: ## movl %ebp,%eax ## addl $IBASE,%eax pushl %eax pushl $cscanfformat call scanf addl $8, % cscan.. addr ipower 20

21 ## printf("enter the base: ") pushl $cprompt1 call printf addl $4, % ## scanf("%d", &) leal IBASE(%ebp), %eax ## Alternative to leal: ## movl %ebp,%eax ## addl $IBASE,%eax pushl %eax pushl $cscanfformat call scanf addl $8, % addl $8, % eip cscan.. addr ipower 21

22 ## printf("enter the base: ") pushl $cprompt1 call printf addl $4, % ## scanf("%d", &) leal IBASE(%ebp), %eax ## Alternative to leal: ## movl %ebp,%eax ## addl $IBASE,%eax pushl %eax pushl $cscanfformat call scanf addl $8, % Xeip cscan.. addr ipower 22

23 ## printf("enter the exponent: ") pushl $cprompt2 call printf addl $4, % ## scanf("%d", &) leal IEXP(%ebp), %eax ## Alternative to leal: ## movl %ebp,%eax ## addl $IEXP,%eax pushl %eax pushl $cscanfformat call scanf addl $8, % SAME SEQUENCE OF STEPS FOR THIS BLOCK AS WELL

24 ## ipower = power(, ) pushl IEXP(%ebp) pushl IBASE(%ebp) call power addl $8, % movl %eax, IPOWER(%ebp) IEXP = -8 COPY BY VALUE ipower

25 ## ipower = power(, ) pushl IEXP(%ebp) pushl IBASE(%ebp) call power addl $8, % movl %eax, IPOWER(%ebp) IBASE = -4 COPY BY VALUE ipower

26 ## ipower = power(, ) pushl IEXP(%ebp) pushl IBASE(%ebp) call power addl $8, % movl %eax, IPOWER(%ebp) addl $8, % eip ipower

27 ## ipower = power(, ) pushl IEXP(%ebp) pushl IBASE(%ebp) call power addl $8, % movl %eax, IPOWER(%ebp) Return value is saved in eax register Xeip ipower

28 ## ipower = power(, ) pushl IEXP(%ebp) pushl IBASE(%ebp) call power addl $8, % movl %eax, IPOWER(%ebp) IPOWER = -12 %(%eax) ipower

29 ## printf("%d to the %d power is %d.\n",,, ipower) pushl IPOWER(%ebp) pushl IEXP(%ebp) pushl IBASE(%ebp) pushl $cresult call printf addl $16, % Can you figure out how these instructions will be executed?

30 ## return 0 movl $0, %eax movl %ebp, % popl %ebp ret eax register set to 0 ipower

31 ## return 0 movl $0, %eax movl %ebp, % popl %ebp ret ipower X

32 ## return 0 movl $0, %eax movl %ebp, % popl %ebp ret FFFFFFFF

33 .section ".text" ## ## int power(int, int ) ## Return raised to the power, where and ## are non-negative. ## ## Formal parameter offsets:.equ IBASE, 8.equ IEXP, 12 You can define aliases for the same name ## Local variable offsets:.equ IPOWER, -4.equ IINDEX, -8.type power,@function

34 power: pushl movl %ebp %, %ebp Init stack ## int ipower = 1 pushl $1 ## int iindex subl $4, % Push local variables ## iindex = 1 movl $1, IINDEX(%ebp) ## return ipower movl IPOWER(%ebp), %eax movl %ebp, % popl %ebp ret Set return value to EAX Restore stack Return

35 Good Luck! Assignment 4 is due this Wednesday 35