1. Practical Session 7

2. Co-Routines

3. Co-routine state

4. Variable Decleration STKSZ equ 16*1024 section .bss CODEP equ 0
FLAGSP equ 4
SPP equ 8
section .rodata
align 16
global numco
numco: dd 3
CORS: dd CO1
dd CO2
dd CO3
section .data
; Structure for first co-routine
CO1: dd Function1
Flags1: dd 0
SP1: dd STK1+STKSZ
; Structure for second co-routine
CO2: dd Function1
Flags2: dd 0
SP2: dd STK2+STKSZ
; Structure for third co-routine
CO3: dd Function2
Flags3: dd 0
SP3: dd STK3+STKSZ
; Counter
COUNTER: dd 0
MAX_ITER: dd 3
section .bss
align 16
CURR: resd 1
SPT: resd 1
SPMAIN: resd 1
STK1: resb STKSZ
STK2: resb STKSZ
STK3: resb STKSZ

5. Co-routine structure

6. Co-routine structure

7. Variables STKSZ – Stack Size CODEP – Code Position: Offset to code
FLAGP – Flag Position: Offset to flags
SPP – Stack Pointer Position: Offset to stack pointer
numco – Number of Co-Routines: Global
CORS –Co-Routines Array
COi – Function Address of Co-Routine i
Flagsi – Flags of Co-Routine i
SPi – Stack Pointer of Co-Routine i
STKi – The Stack of Co-Routine i
SPMain – Stack Pointer of Main Function
CURR – Current Co-Routine
SPT – Temporary Storage for Stack Pointer

8. Initializtion section .text
align 16
extern printf
global init_co_from_c
global start_co_from_c
global end_co
; Initalize a co-routine number given as an argument from C
init_co_from_c:
push EBP
mov EBP, ESP
push EBX
mov EBX, [EBP+8]
mov EBX, [EBX*4+CORS]
call co_init
pop EBX
pop EBP
ret
; EBX is pointer to co-routine structure to initialize
co_init:
pusha
bts dword [EBX+FLAGSP],0 ; test if already initialized
jc init_done
mov EAX,[EBX+CODEP] ; Get initial PC
mov [SPT], ESP
mov ESP,[EBX+SPP] ; Get initial SP
mov EBP, ESP ; Also use as EBP
push EAX ; Push initial "return" address
pushf ; and flags
pusha ; and all other regs
mov [EBX+SPP],ESP ; Save new SP in structure
mov ESP, [SPT] ; Restore original SP
init_done:
popa
ret

9. Co-routine initialization

10. Co-routine initialization

11. Co-routine initialization

12. Function1 ; This function used as code for co-routines 0 and 1
push dword 0
push dword 1
push dword [CORS+8]
push dword [CURR]
push dword FMT1
call printf
add ESP, 20
mov EBX, [CORS+8]
call dword resume
mov dword [COUNTER], 0
func1_loop:
push dword [COUNTER]
push 2
add ESP, 20
add dword [COUNTER], 1
mov eax, [MAX_ITER]
cmp [COUNTER], eax
jne func1_loop
jmp end_co

13. Function2 ; This function used as code for co-routine 2
push dword 0
push dword 1
push dword [CORS]
push dword [CURR]
push dword FMT2
call printf
add ESP, 16
mov EBX, [CORS]
call dword resume
mov dword [COUNTER], 0
func2_loop:
push dword [COUNTER]
push dword 2
push dword [CORS+4]
add ESP, 20
add dword [COUNTER], 1
mov eax, [MAX_ITER]
cmp [COUNTER], eax
jne func2_loop
mov EBX, [CORS+4]
call dword resume
push dword 3
push dword [CORS]
push dword [CURR]
push dword FMT2
call printf
add ESP, 16
mov EBX, [CORS]
push dword 4
push dword [CORS+4]
jmp end_co

14. Co-routine code (function)

15. Co-routine code (function)

16. Resume
; EBX is pointer to co-init structure of co-routine to be resumed
; CURR holds a pointer to co-init structure of the curent co-routine
resume:
pushf ; Save state of caller
pusha
mov EDX, [CURR]
mov [EDX+SPP],ESP ; Save current SP
do_resume:
mov ESP, [EBX+SPP] ; Load SP for resumed co-routine
mov [CURR], EBX
popa ; Restore resumed co-routine state
popf
ret ; "return" to resumed co-routine!

17. Co-routine resume

18. Co-routine resume

19. Start and End ; C-callable start of the first co-routine
start_co_from_c:
push EBP
mov EBP, ESP
pusha
mov [SPMAIN], ESP ; Save SP of main code
mov EBX, [EBP+8] ; Get number of co-routine
mov EBX, [EBX*4+CORS] ; and pointer to co-routine structure
jmp do_resume
; End co-routine mechanism, back to C main
end_co:
mov ESP, [SPMAIN] ; Restore state of main code
popa
pop EBP
ret

20. Start Co-routine scheduler

21. Example CURR SPT SPMAIN STK1 STK2 STK3 numco CORS Function1 CO1 Flags1
Flags1
SP1
CO2
Flags2
SP2
Function2
CO3
Flags3
SP3
COUNTER 3
MAX_ITER

22. After Init CURR SPT SPMAIN STK1 Registers Flags Function1 STK2 STK3
numco
CORS
Function1
CO1 1
Flags1
SP1
CO2
Flags2
SP2
Function2
CO3
Flags3
SP3
COUNTER 3
MAX_ITER

23. Resuming CO2 CURR SPT SPMAIN STK1 Registers Flags Addr1 STK2 ESP ……….
numco
CORS
Function1
CO1 1
Flags1
SP1
CO2
Flags2
SP2
Function2
CO3
Flags3
SP3
COUNTER 3
MAX_ITER
resume:
pushf pusha
mov EDX, [CURR]
mov [EDX+SPP],ESP
do_resume:
mov ESP, [EBX+SPP] mov [CURR], EBX
popa popf
ret

24. Resuming – Resume is Called
CO2
CURR
SPT
SPMAIN
STK1
Registers
Flags
Addr1
STK2
ESP
Addr2
……….
STK3
Addr3
numco
CORS
Function1
CO1 1
Flags1
SP1
CO2
Flags2
SP2
Function2
CO3
Flags3
SP3
COUNTER 3
MAX_ITER
resume:
pushf pusha
mov EDX, [CURR]
mov [EDX+SPP],ESP
do_resume:
mov ESP, [EBX+SPP] mov [CURR], EBX
popa popf
ret

25. Resuming CO2 CURR SPT SPMAIN STK1 Registers Flags Addr1 ESP STK2
……….
STK3
Addr3
numco
CORS
Function1
CO1 1
Flags1
SP1
CO2
Flags2
SP2
Function2
CO3
Flags3
SP3
COUNTER 3
MAX_ITER
resume:
pushf pusha
mov EDX, [CURR]
mov [EDX+SPP],ESP
do_resume:
mov ESP, [EBX+SPP] mov [CURR], EBX
popa popf
ret

26. Resuming CO2 CURR SPT SPMAIN STK1 Registers Flags Addr1 ESP STK2
……….
STK3
Addr3
numco
CORS
Function1
CO1 1
Flags1
SP1
CO2
Flags2
SP2
Function2
CO3
Flags3
SP3
COUNTER 3
MAX_ITER
resume:
pushf pusha
mov EDX, [CURR]
mov [EDX+SPP],ESP
do_resume:
mov ESP, [EBX+SPP] mov [CURR], EBX
popa popf
ret

27. Resuming CO2 CURR SPT SPMAIN STK1 Registers Flags Addr1 STK2 Addr2
……….
STK3
ESP
Addr3
numco
CORS
Function1
CO1 1
Flags1
SP1
CO2
Flags2
SP2
Function2
CO3
Flags3
SP3
COUNTER 3
MAX_ITER
resume:
pushf pusha
mov EDX, [CURR]
mov [EDX+SPP],ESP
do_resume:
mov ESP, [EBX+SPP] mov [CURR], EBX
popa popf
ret

28. Resuming CO3 CURR SPT SPMAIN STK1 Registers Flags Addr1 STK2 Addr2
……….
STK3
ESP
Addr3
numco
CORS
Function1
CO1 1
Flags1
SP1
CO2
Flags2
SP2
Function2
CO3
Flags3
SP3
COUNTER 3
MAX_ITER
resume:
pushf pusha
mov EDX, [CURR]
mov [EDX+SPP],ESP
do_resume:
mov ESP, [EBX+SPP] mov [CURR], EBX
popa popf
ret

29. Resuming CO3 CURR SPT SPMAIN STK1 Registers Flags Addr1 STK2 Addr2
……….
STK3
ESP
Addr3
numco
CORS
Function1
CO1 1
Flags1
SP1
CO2
Flags2
SP2
Function2
CO3
Flags3
SP3
COUNTER 3
MAX_ITER
resume:
pushf pusha
mov EDX, [CURR]
mov [EDX+SPP],ESP
do_resume:
mov ESP, [EBX+SPP] mov [CURR], EBX
popa popf
ret