1 IKI10230 Pengantar Organisasi Komputer Kuliah no. 08: Multi-module Programs Sumber: 1. Paul Carter, PC Assembly Language 2. Hamacher. Computer Organization, ed-5 3. Materi kuliah CS61C/2000 & CS152/1997, UCB 7 April 2004 L. Yohanes Stefanus Bobby Nazief bahan kuliah:

2 REVIEW: Loop (2) °the following pseudo-code: sum = 0; for ( i=0; i<10; i++ ) sum += i; °could be translated into assembly as: 1. mov eax, 0; eax is sum 2. mov ecx, 0; ecx is i 3.loop_start: 4. add eax, ecx 5. inc ecx 6. cmp ecx,10 7. jne loop_start °implementasi dgn loop: (salah satu alternatif) 1. mov eax, 0; eax is sum 2. mov ecx, 10; ecx is (10-i) 3. mov edx, 0; edx is i 4.loop_start: 5. add eax, edx 6. inc edx 7.loop loop_start

3 KOREKSI: sub3.asm (Passing Parameters via Stack Frame) push edx ; save i on stack push dword input; push address on input on stack call get_int add esp, 8 ; remove i and &input from stack; subprogram get_int... ; Parameters (in order pushed on stack) ; number of input (at [ebp + 12]) ; address of word to store input into (at [ebp + 8]) ; Notes: ; values of eax and ebx are destroyed get_int: push ebp mov ebp, esp mov eax, [ebp + 12] call print_int... call read_int mov ebx, [ebp + 8] mov [ebx], eax ; store input into memory pop ebp ret ; jump back to caller [ESP][EBP] [ESP+4][EIP] [ESP+8][input] [ESP+12][edx]

4 SubPrograms/SubRoutines/Functions

5 Subroutine °Contoh dalam program bahasa C: int add_scale(int x, int y, int sc) { int result; result = x + sc * y; return result; } main() { int avec[3], bvec[3], cvec[3], scale;... for (i = 0; i < 3; i++) cvec[i] = add_scale(avec[i], bvec[i], scale);... }

6 Use of CALL & RET in Subroutine Invocation _add_scale:... mov eax,[ebp+16] imul eax,[ebp+12] add eax,[ebp+8]... ret _main:... L4: cmp [ebp-44],2; cmp(i, 2) jle L7; i < 2 jmp L5 L7: mov eax,[ebp-40]; scale push eax... mov eax,[eax+edx]; bvec[i] push eax... mov eax,[eax+edx]; avec[i] push eax call _add_scale... mov [edx+ecx],eax; cvec[i]...

7 Parameter Passing between Calling- & Callee-subroutines

8 Passing Parameters 1.By Value 2.By Reference

9 Passing Parameters By Value int add_scale(int x, int y, int scale) { int result; result = x + scale * y; return result; } main() { int avec[3], bvec[3], cvec[3], scale;... for (i = 0; i < 3; i++) cvec[i] = add_scale(avec[i], bvec[i], scale);... }

10 Passing Parameters By Reference void v_add_scale(int x[ ], int y[ ], int z[ ], int scale) { for (i = 0; i < 3; i++) z[i] = add_scale(x[i], y[i], scale); } main() { int avec[3], bvec[3], cvec[3], scale;... v_acc_scale(avec, bvec, cvec, scale); /* cvec change after the call! */... }

11 Implementation of Passing Parameters °Via Register °Via Stack

12 Passing Values via Registers _main: mov esi,[Scale] mov edx,0 L1: mov ecx,AVEC mov eax,[ecx+4*edx] add ecx,4*3 mov ebx,[ecx+4*edx] call _add_scale add ecx,4*3 mov [ecx+4*edx],edi inc edx cmp edx,3 jb L1 _add_scale: mov edi,esi imul edi,ebx add edi,eax ret

13 Passing References via Registers _main: mov eax,AVEC mov ebx,BVEC mov ecx,CVEC mov esi,[Scale] call _v_add_scale... _v_add_scale: mov edx,0 L1: mov edi,esi imul edi,[ebx+4*edx] add edi,[eax+4*edx] mov [ecx+4*edx],edi inc edx cmp edx,3 jb L1 ret

14 Use of Stack °To pass parameters due to limited number of registers most HLLs use it as “standard” mechanism, known also as calling conventions -assembly programs/modules need to use these conventions to be able to communicate with HLL programs data are accessed from the stack directly instead of via POP instruction: mov eax,[esp+4]; esp as pointer or, Intel has provided EBP register for this purpose mov ebx,[ebp+4]; ebp as pointer °To store local variables func() { int x, y;... }

15 Stacks as Storage for Local Variables

16 Stack as Storage for Local Variables °Local variables live only as long as its function/ subroutine, where these variables reside, live (i.e., from the time the function/subroutine is called, until it returns execution to the calling program) °Accordingly, memory allocation for local variables does not need to be for the duration of the whole program:  Stack is the convenient location for this temporary storage  Local variables are allocated on the stack, by extending the stack-frame used whenever a subroutine-call takes place (where return- address is placed)

17 General Form of a Subroutine subroutine_label: push ebp; save original EBP value on stack mov ebp,esp; new EBP = ESP, needed to access ; parameters passed by the calling program sub esp,LOCAL_BYTES ; = # bytes needed by locals ; subprogram code mov esp,ebp; deallocate locals pop ebp; restore original EBP value ret ESPLocVar-m... EBP-4LocVar-1 EBP[EBP] [EIP caller ] EBP+8Par-1... Par-n

18 Example: calc_sum.c void calc_sum( int n, int *sump ) { int i, sum = 0; for ( i=1; i <= n; i++ ) sum += i; *sump = sum; }

19 Example: calc_sum.asm cal_sum: push ebp mov ebp, esp sub esp, 4 mov dword [ebp - 4], 0; sum = 0 mov ebx, 1; i = 1 for_loop: cmp ebx, [ebp+12]; is i >= n? jnle end_for add [ebp-4], ebx; sum += i inc ebx; i++ jmp short for_loop end_for: mov ebx, [ebp+8]; ebx = sump mov eax, [ebp-4]; eax = sum mov [ebx], eax; *sump = sum mov esp, ebp pop ebp ret ESP = EBP-4Sum EBP[EBP] [EIP caller ] EBP+8sump EBP+12N

20 General Form of a Subroutine using Enter/Leave subprogram_label: enter LOCAL_BYTES, 0; = # bytes needed by locals ; subprogram code leave ret °bandingkan dengan: subroutine_label: push ebp; save original EBP value on stack mov ebp,esp; new EBP = ESP, needed to access ; parameters passed by the calling program sub esp,LOCAL_BYTES ; = # bytes needed by locals ; subprogram code mov esp,ebp; deallocate locals pop ebp; restore original EBP value ret

21 Passing Parameters via Stack Frames

22 Passing Values via Stack Frames (1/2) int add_scale(int x, int y, int scale) { int result; result = x + scale * y; return result; } main() { int avec[3], bvec[3], cvec[3], scale;... for (i = 0; i < vec_length; i++) cvec[i] = add_scale(avec[i], bvec[i], scale);... }

23 LEA Instruction °Load Effective Address °LEAREG,MEMLOC; REG  MEMLOC LEAEAX,[VAR1]; EAX  VAR1 -MOVEAX,VAR1 LEAEAX,[EBX+ESI]; EAX  [EBX] + [ESI] °Bandingkan dengan: MOVEAX,[VAR1]; EAX  [VAR1] MOVEAX,[EBX+ESI]; EAX  [[EBX] + [ESI]]

24 Passing Values via Stack Frames (2/2) _main: L4:cmp [ebp-44],2; cmp(i, 2) jle L7; i < 2 jmp L5 L7: mov eax,[ebp-40]; scale push eax... lea eax,[4*edx] lea edx,[ebp-24]; bvec mov eax,[eax+edx]; bvec[i] push eax... lea eax,[4*edx] lea edx,[ebp-12] ; avec mov eax,[eax+edx] ; avec[i] push eax call _add_scale... lea edx,[4*ecx] lea ecx,[ebp-36] ; cvec mov [ecx+edx],eax ; cvec[i]... inc [ebp-44]; i += 1 jmp L4 L5: _add_scale: push ebp mov ebp,esp sub esp,24 mov eax,[ebp+16] imul eax,[ebp+12] mov edx,[ebp+8] add edx,eax mov [ebp-4],edx mov edx,[ebp-4] mov eax,edx mov esp,ebp pop ebp ret EBP  [EBP] [EIP] EBP+8  Avec[i] EBP+12  Bvec[i] EBP+16  Scale

25 Passing References via Stack Frames (1/2) void v_add_scale(int x[ ], int y[ ], int z[ ], int scale) { for (i = 0; i < vec_length; i++) z[i] = add_scale(x[i], y[i], scale); } main() { int avec[3], bvec[3], cvec[3], scale;... v_acc_scale(avec, bvec, cvec, scale);... }

26 Passing References via Stack Frames (2/2) _main: mov eax,[ebp-40] push eax lea eax,[ebp-36] push eax lea eax,[ebp-24] push eax lea eax,[ebp-12] push eax call _v_add_scale add esp,16 _v_add_scale:... L4: cmp [ebp-4],2 jle L7 jmp L5 L7: mov eax,[ebp+20]; scale push eax mov eax,[ebp-4] lea edx,[4*eax] mov eax,[ebp+12]; BVEC mov edx,[eax+edx]; BVEC[i] push edx... mov eax,[ebp+8]; AVEC mov edx,[eax+edx]; AVEC[i] push edx call _add_scale... mov edx,[ebp+16] mov [edx+ecx],eax inc [ebp-4] jmp L4 L5:... ret

27 Multi-module Programs

28 Multi-module Programs °A multi-module program is one composed of more than one object file. tugas0a.exe: driver.o tugas0a.o asm_io.o {C library} °Combined by the linker gcc –o tugas0a.exe driver.o tugas0a.o asm_io.o {C library} °The linker must match up references made to each label in one module (i.e. object file) to its definition in another module Calling-module declare the called-label “extern” Called-module declare the called-label “global”

29 Example °AddScale.asm: global _add_scale _add_scale:... mov eax,[ebp+16] imul eax,[ebp+12] add eax,[ebp+8]... ret °Main.asm: global _main extern _add_scale _main:... L4:... mov eax,[eax+edx]; bvec[i] push eax... mov eax,[eax+edx]; avec[i] push eax call _add_scale

30 On Pop-Quiz #1

31 No. 3 °Jika diketahui variabel X adalah sebuah integer (4 byte) dengan alamat 0xBFFE. Sistem komputernya menggunakan format Little-Endian untuk menyimpan data multi-byte dalam memori yang byte- addressable. Berapa nilai X? 0xBFFD00h 0xBFFE34h 0xBFFF12h 0xC00000h 0xC00143h 0xC00212h 0xC00300h 0xC00400h

32 No. 4 °Var i = 1001b (integer 4-bit) dan j = b (integer 8- bit), keduanya menggunakan representasi komplemen-2. Hitung k = i + j! (nyatakan dalam biner) i = 1001 = = -7 j = = 16 k = = 9

33 No. 5 °Perhatikan bagian program berikut: segment.data var_add h var_adb 11h,22h,33h,44h segment.text mov esi,var_a mov al,[esi]; esi = 1000, al = 11 inc esi; esi = 1001 add[esi],al; [esi] lama = 22, al = 11 ; [esi] b aru = 33 addesi,2; esi = 1003 sub[esi],al; [esi] lama = 44, al = 11 ; [esi] baru = 33 ; [var_a] = 11, Var_a = 0x100011h 0x100133h 0x100233h 0x100333h