1

Quick look at pdp-11 CPU

제 24 강 : Process Image

2

Chapter Two

CPU registers• Two kinds of stack

– Case: Fixed size Case: Variable size

• SP: Stack Pointer SP: Stack Pointer EP: Environment Pointer (boundary or size)

• Stack & Function call frameCall argument Local variableReturn address Register save

bottom

top - SP

bottom

top - SP

EPmain(){ x= sin (arg); - - - y= sin (arg);}

sin (arg);{ local var; expression; return;}

pop this portion

3

pdp-11 CPU has 2 SP’s main()

do_a()

do_b()

read()

read()

do_p()

do_q()

do_r()

kernel

lsmain()do_a()do_b()read()

read()do_p()do_q()do_r()

sys call

user stack

kernel stack

SP

SP

Base

Base

4

Protection (multi-user) prevent R/W/Jump to other process’ image confine memory access intercept faulty accessScattered Allocation image can be scatteredAllow Relocation during swapping, not on-demand paging

Why pdp-11 needs MMU(memory management

unit)

CPU Memory

CPU MemoryMMU

Physical Address

VA

loc 0

PA

loc 2000

PAR: Page Address Register (maps VA to PA)

PAR2000

30002500

Mapping Tablefor a.out

5

• Physical memory was divided up into 8K byte pages• memory space/process = 64Kbytes = 8 pages• Max 8 PAR’s per process• Access mode (R|W|...) per page PDR (Page Description Register) & PAR Pair

• Allocate contiguous chunk of physical memory for each process

Split up this chunk into 3 pieces text data areas stack

• Unix may have used just three PAR|PDR’s

stack

data

text

XX

WW

W

W

W

01

23

4

5

7

6

PAGES

PDRreadwrite

PAR2000

30002500

con

tig

uou

s

pag

es

6

PAR PDR

<active USER >

PAR PDR

< KERNEL>

sha.out

via.out

kernela.out

Memory

2 sets of memory mapping registers

7

CPU

PCB

mem disk

user

PCB

tty

sh vi mail

CPU mem disk tty

Kernel a.out

Hardware

proc

K-stack

Remember?Kernel has PCB for each

application

8

Kernel’s PCB in detail

sh

vi

kernel

PCB(sh)PCB(vi)PCB(ls)

logicaladdress

ls

user

proc

K-stack

proc [NPROC]

user

kernel

stack

struct user & k-stackshare single page

1 page / process“ppda”

(per process data area)

sh

ls vi

user

proc

K-stack

9

Kernel’s PCB layout

sh

vi

kernelproc[ ]

ls

u stack

u stack

u stack

logicaladdress

1 page per each process (ppda)

1 global array for all processes

user

kernel

stack

10

scatter ppda in physical address space

sh

vi

kernelproc

ls

u stack

u stack

u stack

logicaladdress

sh

vi

kernelproc

ls

u stack

u stack

u stack

physicaladdress

logically contiguousphysically scattered adjacent to application’s image

(ppda)1 page

perprocess

11

each proc[ ] points to application’s ppda

sh

vi

kernelproc

ls

u stack

u stack

u stack

kernelproc

struct proc { p_addr; p_size; }

sh

vi

ls

u stack

u stack

u stack

ppdaaddress

logicaladdress

physicaladdress

sizeof

swappable

12

sha.out

via.out

kernela.out

proc[0]proc[i]proc[k]

kernel

a.outproc[0]proc[i]proc[k]

= 10000

= 20000

= 30000

20000 loc. 0

loc. 0Physical AddressLogical Address

30000 ppda

ppda

sh

vi

ls

u stack

u stack

u stack ppda

50000

13

PAR PDR

<Active USER >

PAR PDR

< KERNEL>

sha.out

via.out

u--stack

u--stack

Kernel

a.out

struct user k-stack

struct user k-stack

struct user k-stack

2 sets of {PAR|PDR}

14

PAR PDR

< KERNEL>

sha.out

via.out

u--stack

u--stack

Kernel

a.out

struct user k-stack

struct user k-stack

struct user k-stack

kernel 7th mapping register

Points to active process ppda (7-3-1-b)

Hence, in Lion’s code

“u ” always points to struct user ofthe current active process

(cf. proc[PID])

Kernel’s 7th PAR active user’s ppda

PAR PDR

<Active USER >

15

main, icode

16

PAR PDR

< USER >

PAR PDR

< KERNEL>

sha.out

via.out

u--stack

u--stack

Kernel

Proc[0]Proc[i]Proc[k]

struct user k-stack

struct user k-stack

struct user k-stack

proc[i].p_addr is

address of process i’s

ppda

struct user

image

7-th reg == ppda of active process

17

sh(parent)

ls(child)

At this point, context switch: Kernel 7th PAR points to new ppda

--------User PAR/PDR also changes

estabur() sureg()

PAR PDR

< USER >

PAR PDR

lsa.out

sha.out

u--stack

u--stack

Kernel

a.out

struct user k-stack

struct user k-stack

struct user k-stack

18

CPU mem disk

user

Process sh Process vi Process ls

CPU mem disk

User a.out

Kernel a.out

K-stack

“ppda”(per processdata area)

kernel space7-th kernel page

Data Segment(swappable)

* (7-2, 7-3)

address of 7-th kernel page (ppda) address of active process

user

proc

K-stack

proc PROC[ ]

PPDA (7-th page)user

K-stack

proc

user

kernel

stack

7-th page

19

text

data

bss

p_addr

(7-th kernel page)

p_size

Process Image

bss: allocated at load time, init to zero

struct user: located adjacent to program segment

but is part of kernel address space

proc[i]

u-stack

struct user

k-stack

a.out

ppdaSwappable

Image

(data segment)

Process

Image

20

• data segment (swappable image) (7-3)• allocated as one single segment (physically contiguous – for swap)

• ppda (per process data area) (7-3)• 7th page of kernel • lower end -- struct "user“• higher end -- kernel mode stack

• proc[PID].p_addr, p_size (7-2)• address of process (swappable image) (whether in core or disk)

• 7-th kernel (segmentation address) register points to <= proc[i].p_addr (address of the process)

user

kernel

stack

7-th page

21

PAR PDR

< KERNEL>

sha.out

via.out

kernela.out

proc[0]proc[i]proc[k]

ppda pda(sh) (vi)

loc. 0

sha.out

via.out

kernel

a.outproc[0]proc[i]proc[k]

struct userk-stack(sh)

struct user k-stack(vi)

= 10000

= 20000

= 30000

30000

10000

20000

loc. 0

loc. 0

Physical AddressLogical Address

ppda (sh)

ppda (vi)

7-th page p p d a of Active

processowned bykernel

adjacent toapplication, for swapping

22

PAR PDR

< KERNEL>

sha.out

via.out

kernela.out

proc[0]proc[i]proc[k]

ppda pda(sh) (vi)

loc. 0

sha.out

via.out

kernel

a.outproc[0]proc[i]proc[k]

struct user k-stack(sh)

struct user k-stack(vi)

= 10000

= 20000

= 30000

30000

10000

20000

loc. 0

loc. 0

Physical AddressLogical Address

ppda

ppda

7-th page

SwappableImage

“data segment”(7-3)

a.out

PAR PDR

< USER >

23

a.out

u-stack

proc[i] proc[j] proc[k] …

userk-stack

a.out

u-stack

userk-stack

a.out u-stack

userk-stack

PAR PDR

USER

PAR PDR

KERNEL

sh vi sim

Adjacent

Belongs

p_addr p_addr

24

CPU state3 types of CPU registers

• with address– memory mapping PAR|PDR– instruction address PC– stack SP EP

• with data – R0 R1 R2 R3 …

• with others (status)– PSW (ZNCOM ..)

CPU

R0 R1 | SP E P PC

PAR PDR

USER

PAR PDR

KERNEL

< CPU State >

25

PAR PDR

KERNEL

7

7th Register

R0R1 |R4EPSPPC

k sha.out

via.out

u--stack

u--stack

Kernel

a.out

struct user k-stack

Physical Address

struct userk-stack (vi)

struct userk-stack (sh)

points to p.p.d.a. ofactive process

(base of kernel stack)

top of kernel st

ack

kernel stack fra

me boundary

U

user stack

CPU Registers

Mapping Registers

7-th kernel mapping register (6-2)

26

PAR PDR

< USER >

PAR PDR

< KERNEL>

Kernel

Proc[0]

struct user k-stack

proc[i].p_addr is

address of process i’s struct user

ppda

image

7-th ksar == ppda of active process

After the boot/init,

7-th ksar = proc #0 (kernel process)

(1589) (6-3-1-b) (6-3-3-b)