Computer Architecture and Assembly Language. Practical Session 7

Transcription

1 Computer Architecture and Assembly Language Practical Session 7

2 Co-Routines co-routines are assembly implementation of threads each co-routine decides to which co-routine to pass a control (unlike usual threads) We would implement silly round robin scheduling algorithm: main() scheduler co-routine1 scheduler co-routine2 scheduler co-routine1 scheduler co-routine2 scheduler main()

3 Co-routine state co-routine is denoted by Coi (i is co-routine s id) scheduler is also a co-routine co-routine suspends itself after some time slice co-routine resumes a scheduler co-routine should save its current state before it suspends itself (in order to continue its execution later) stack state registers flags stack pointer (ESP) instructions pointer (EIP)

4 Co-routine structure We define an array of co-routines structures: why SPi points to the end of stack? Co-routine structure: to be able to use push and pop stack functionality with ESP STKSIZE equ 16*1024 STKi: resb STKSIZE ;(16 Kb) COi: dd Functioni ; pointer to co-routine function : dd 0 ; 0 if co-routine is not initialized, 1 otherwise SPi: dd STKi + STKSIZE ; pointer to the beginning of co-routine stack Funci 0 SPi co-routine structure co-routine stack

5 STKSZ equ 16*1024 ; co-routine stack size CODEP equ 0 ; offset of pointer to co-routine function in co-routine structure FLAGSP equ 4 ; offset of pointer to flags co-routine structure SPP equ 8 ; offset of pointer to co-routine stack in co-routine structure section.rodata align 16 global numco numco: dd 3 CORS: dd CO1 dd dd section.data align 16 CO1: dd Function1 ; structure for first co-routine 1: dd 0 SP1: dd STK1+STKSZ : dd Function1 ; structure for second co-routine 2: dd 0 SP2: dd STK2+STKSZ : dd Function2 ; structure for third co-routine 3: dd 0 SP3: dd STK3+STKSZ section.bss align 16 CURR: resd 1 SPT: resd 1 ; temporary stack pointer variable SPMAIN: resd 1 ; stack pointer of main STK1: resb STKSZ STK2: resb STKSZ STK3: resb STKSZ Variables Declaration

6 Co-routine initialization - save initial co-routine state init_co_from_c: ebx, [ebp+8] ebx, [4*ebx + CORS] call co_init co_init: eax, [ebx+codep] esp, [EBX+SPP] push eax [ebx+spp], esp ; get co-routine ID number ; get COi pointer ; get initial PC ; get initial SP ; push initial return address ; push flags ; push all other registers ; save new SPi value (after all the pushes) main() { /* initialize co-routines*/ } for(i = 0; i < numco; i++) init_co_from_c(i); /* start a scheduler co-routine*/ start_co_from_c (2); Funci 0 SPi co-routine structure co-routine stack

7 Co-routine initialization - save initial co-routine state init_co_from_c: ebx, [ebp+8] ebx, [4*ebx + CORS] call co_init co_init: eax, [ebx+codep] esp, [EBX+SPP] push eax [ebx+spp], esp ; get co-routine ID number ; get COi pointer ; get initial PC ; get initial SP ; push initial return address ; push flags ; push all other registers ; save new SPi value (after all the pushes) main() { /* initialize co-routines*/ } for(i = 0; i < numco; i++) init_co_from_c(i); /* start a scheduler co-routine*/ start_co_from_c (2); ESP Funci 0 SPi co-routine structure co-routine stack

8 Co-routine initialization - save initial co-routine state init_co_from_c: ebx, [ebp+8] ebx, [4*ebx + CORS] call co_init co_init: eax, [ebx+codep] esp, [EBX+SPP] push eax [ebx+spp], esp ; get co-routine ID number ; get COi pointer ; get initial PC ; get initial SP ; push initial return address ; push flags ; push all other registers ; save new SPi value (after all the pushes) main() { /* initialize co-routines*/ } ESP for(i = 0; i < numco; i++) init_co_from_c(i); /* start a scheduler co-routine*/ start_co_from_c (2); Funci 0 SPi Funci co-routine structure co-routine stack

9 Co-routine initialization - save initial co-routine state init_co_from_c: ebx, [ebp+8] ebx, [4*ebx + CORS] call co_init co_init: eax, [ebx+codep] esp, [EBX+SPP] push eax [ebx+spp], esp ; get co-routine ID number ; get COi pointer ; get initial PC ; get initial SP ; push initial return address ; push flags ; push all other registers ; save new SPi value (after all the pushes) ESP main() { /* initialize co-routines*/ } for(i = 0; i < numco; i++) init_co_from_c(i); /* start a scheduler co-routine*/ start_co_from_c (2); Funci 0 SPi E Funci co-routine structure co-routine stack

10 Co-routine initialization - save initial co-routine state init_co_from_c: ebx, [ebp+8] ebx, [4*ebx + CORS] call co_init co_init: eax, [ebx+codep] esp, [EBX+SPP] push eax [ebx+spp], esp ; get co-routine ID number ; get COi pointer ; get initial PC ; get initial SP ; push initial return address ; push flags ; push all other registers ; save new SPi value (after all the pushes) ESP main() { /* initialize co-routines*/ } for(i = 0; i < numco; i++) init_co_from_c(i); /* start a scheduler co-routine*/ start_co_from_c (2); Funci 0 SPi registers E Funci co-routine structure co-routine stack

11 Co-routine initialization - save initial co-routine state init_co_from_c: ebx, [ebp+8] ebx, [4*ebx + CORS] call co_init co_init: eax, [ebx+codep] esp, [EBX+SPP] push eax [ebx+spp], esp ; get co-routine ID number ; get COi pointer ; get initial PC ; get initial SP ; push initial return address ; push flags ; push all other registers ; save new SPi value (after all the pushes) ESP main() { /* initialize co-routines*/ } for(i = 0; i < numco; i++) init_co_from_c(i); /* start a scheduler co-routine*/ start_co_from_c (2); Funci 1 SPi registers E Funci co-routine structure co-routine stack

12 Co-routine initialization section.text align 16 extern printf global init_co_from_c global start_co_from_c global end_co init_co_from_c: push EBP EBP, ESP push EBX EBX, [EBP+8] ; EBX contains a number of the co-routine to be initialized EBX, [EBX*4+CORS] ; EBX contains a pointer to co-routine structure to be initialized call co_init pop EBX pop EBP ret co_init: bts dword [EBX+FLAGSP],0 ; test if already initialized jc init_done EAX,[EBX+CODEP] ; get initial PC [SPT], ESP ; save original SP ESP,[EBX+SPP] ; get initial SP EBP, ESP ; also use as EBP push EAX ; push initial "return" address (initial PC) ; push flags ; push all other registers [EBX+SPP],ESP ; save new SP in structure ESP, [SPT] ; restore original SP init_done: popad bts instruction tests one bit of its first operand, whose index is ret given by the second operand, and stores the value of that bit in the carry flag (CF). In addition, bts sets the bit to be 1.

13 Start co-routine scheduler We start scheduling by suspending main() and resuming a scheduler co-routine. start_co_from_c: push EBP EBP, ESP [SPMAIN], ESP ; save ESP of main () EBX, [EBP+8] EBX, [EBX*4 + CORS] jmp do_resume main() { /* initialize co-routines*/ ; gets ID number of a scheduler ; gets a pointer to a scheduler structure ; resume a scheduler co-routine } for(i = 0; i < numco; i++) init_co_from_c(i); /* start a scheduler co-routine*/ start_co_from_c (2); We end scheduling by going back to main(). end_co: ESP, [SPMAIN] ; restore state of main code popad pop EBP ret

14 Scheduler co-routine function Scheduler function is started by main. scheduler_function: pick up some thread ID i EBX, [CORS + i*4] call resume ; resumes Coi pick up some other thread ID j EBX, [CORS + j*4] ; resumes Coj call resume jmp end_co ; resume main call resume save a state of the current co-routine resume a state of the next co-routine (EBX should contain a pointer to it) EBX is pointer to co-init structure of the co-routine to be resumed. CURR holds a pointer to co-init structure of the current co-routine. after call resume return address (i.e. EIP) is resume: ; save state of caller pushed automatically into (co-routine) stack we only have to save EFLAGS, ESP, and registers EDX, [CURR] [EDX+SPP],ESP ; save current SP do_resume: ; load SP for resumed co-routine ESP, [EBX+SPP] [CURR], EBX popad ; restore resumed co-routine state popfd ret ; "return" to resumed co-routine!

15 Function2 This function used as code for co-routine 3 (scheduler) FMT2: db "Function2, co %lx, called by %lx, pass %ld", 10, 0 Function2: push dword 1 push dword [CORS] ; indeed, called by main push dword [CURR] push dword FMT2 call printf add ESP, 16 EBX, [CORS] ; resume CO1 call resume push dword 2 push dword [CORS] push dword [CURR] push dword FMT2 call printf add ESP, 16 EBX, [CORS+4] ; resume call resume push dword 3 push dword [CORS+4] push dword [CURR] push dword FMT2 call printf add ESP, 16 EBX, [CORS] ; resume CO1 call resume push dword 4 push dword [CORS] push dword [CURR] push dword FMT2 call printf add ESP, 16 EBX, [CORS+4] ; resume call resume jmp end_co ; resume main

16 Function1 This function used as code for co-routines 1 and 2 FMT1: db "Function1, co %lx, called by %lx, pass %ld", 10, 0 Function1: push dword 1 push dword [CORS+8] push dword [CURR] push dword FMT1 call printf add ESP, 16 EBX, [CORS+8] ; resume a scheduler call resume push dword 2 push dword [CORS+8] push dword [CURR] push dword FMT1 call printf add ESP, 16 EBX, [CORS+8] ; resume a scheduler call resume

17 Run example data declaration.bss.data CURR SPT SPMAIN STK1 3 numco CO1 CORS Function1 CO1 0 1 SP1 STK2 Function1 0 2 SP2 Function2 0 3 STK3 SP3 0 COUNTER 3 MAX_ITER

18 After co-routine initialization.bss.data Function1 Function1 Function2 CURR SPT SPMAIN STK1 STK2 STK3 3 numco CO1 CORS Function1 CO1 1 1 SP1 Function1 1 2 SP2 Function2 1 3 SP3 0 COUNTER 3 MAX_ITER

19 Resuming - right before.bss.data Addr1 CURR SPT SPMAIN STK1 STK2 3 numco CO1 CORS Function1 CO1 1 1 SP1 Function1 1 2 resume: do_resume: popad popfd ret EDX, [CURR] [EDX+SPP],ESP ESP, [EBX+SPP] [CURR], EBX SP2 ESP.. STK3 Function2 1 3 SP3 0 COUNTER 3 MAX_ITER Addr3

20 Resuming resume is called.bss.data Addr1 CURR SPT SPMAIN STK1 STK2 3 numco CO1 CORS Function1 CO1 1 1 SP1 Function1 1 2 resume: do_resume: popad popfd ret EDX, [CURR] [EDX+SPP],ESP ESP, [EBX+SPP] [CURR], EBX ESP Addr2.. STK3 SP2 Function2 1 3 SP3 0 COUNTER 3 MAX_ITER Addr3

21 Resuming backup registers.bss.data ESP Addr1 Addr2.. CURR SPT SPMAIN STK1 STK2 STK3 3 numco CO1 CORS Function1 CO1 1 1 SP1 Function1 1 2 SP2 Function2 1 3 SP3 0 COUNTER resume: do_resume: popad popfd ret EDX, [CURR] [EDX+SPP],ESP ESP, [EBX+SPP] [CURR], EBX 3 MAX_ITER Addr3

22 Resuming backup stack pointer.bss.data ESP Addr1 Addr2.. CURR SPT SPMAIN STK1 STK2 STK3 3 numco CO1 CORS Function1 CO1 1 1 SP1 Function1 1 2 SP2 Function2 1 3 SP3 0 COUNTER resume: do_resume: popad popfd ret EDX, [CURR] [EDX+SPP],ESP ESP, [EBX+SPP] [CURR], EBX 3 MAX_ITER Addr3

23 Resuming - load stack pointer of resume co-routine.bss.data ESP Addr1 Addr2.. CURR SPT SPMAIN STK1 STK2 STK3 3 numco CO1 CORS Function1 CO1 1 1 SP1 Function1 1 2 SP2 Function2 1 3 SP3 0 COUNTER 3 MAX_ITER resume: do_resume: popad popfd ret EDX, [CURR] [EDX+SPP],ESP ESP, [EBX+SPP] [CURR], EBX Addr3

24 Resuming set current co-routine variable.bss.data ESP Addr1 Addr2.. CURR SPT SPMAIN STK1 STK2 STK3 3 numco CO1 CORS Function1 CO1 1 1 SP1 Function1 1 2 SP2 Function2 1 3 SP3 0 COUNTER 3 MAX_ITER resume: do_resume: popad popfd ret EDX, [CURR] [EDX+SPP],ESP ESP, [EBX+SPP] [CURR], EBX Addr3

25 Resuming restore a state of loaded co-routine.bss.data Addr1 Addr2.. CURR SPT SPMAIN STK1 STK2 STK3 3 numco CO1 CORS Function1 CO1 1 1 SP1 Function1 1 2 SP2 Function2 1 3 SP3 0 COUNTER resume: do_resume: popad popfd ret EDX, [CURR] [EDX+SPP],ESP ESP, [EBX+SPP] [CURR], EBX 3 MAX_ITER ESP Addr3

26 Resuming go to execute the loaded co-routine.bss.data Addr1 Addr2.. CURR SPT SPMAIN STK1 STK2 STK3 3 numco CO1 CORS Function1 CO1 1 1 SP1 Function1 1 2 SP2 Function2 1 3 SP3 0 COUNTER resume: do_resume: popad popfd ret EDX, [CURR] [EDX+SPP],ESP ESP, [EBX+SPP] [CURR], EBX 3 MAX_ITER ESP