0-CENG255 Ch2 17-v3 - ece.uvic.cakinli/ceng255/CENG255_Ch2_17-PartIV-revised.pdf · ISA 77 Fig....

KinFunLIUniversityofVictoria

CENG255IntroductiontoComputerArchitecture

ISA55

2.6 Stacks• Astack (pushdownstack)• alistofdataelements• added/removedattopendonly

• Last-in-first-out(LIFO)• Push anewelementontothestacktop• Pop thetopelementfromthestack• Datastack andprocessorstackinmemory



ISA56

2.7.1 Processor Stack• Processorhasstackpointer(SP)registerthatpointstotopoftheprocessorstack• Pushoperationinvolvestwoinstructions:

Subtract SP,SP,#4Store Rj,(SP)

• Popoperationalsoinvolvestwoinstructions:

Load Rj,(SP)Add SP,SP,#4



ISA57

Fig. 2.14 Stack in Memory



ISA58

Stack Varieties• StackGrowth:•Ascending•Descending

• Stackpointer:• Fullstack• Emptystack



ISA59

2.7 Subroutines-1• Aparticulartaskisrepeatedandexecutedmanytimesusingdifferentdata• Examples:mathematicalfunction,listsorting

• Implementtaskinasubroutine• Ratherthanreproduceentiresubroutineblockineachpartofprogram,useasubroutinecall• SpecialtypeofbranchwithCallinstruction



ISA60

Subroutines-2• Branchingtosameblockofinstructionssavesspaceinmemory

• Mustbranchbackafterexecutingthelastinstructioninsubroutine

• UseReturn instruction• Subroutinecanbecalledfromdifferentplacesintheprogram

• HowcanReturn bedonetothecorrectplace?• =>subroutinelinkage



ISA61

2.7.1 Subroutine Linkage• Simplestmethod:placenext(afterCall)instruction’saddressinlinkregister

• Call instructionperformstwooperations:

1. StoreupdatedPCcontentinlinkregister

2. Branchtotarget(subroutine)address

• Return instructionbranchestoaddressinlinkregister



ISA62

Fig. 2.16 Caller and Callee



ISA63

2.7.1 Subroutine Nesting• Asubroutineisallowedtocallanothersubroutine• =>subroutinenesting

• Linkregister=nextaddressoffirstcall• =>overwrittenaftersecondcall

• SaveLinkregister onstackbeforesecondcall• Afterreturnfromsecondsubroutine,restoreslinkregister



ISA64

2.7.2 Parameter Passing• Differentinputdata=>subroutine

• =>differentresults• Parameterpassing:Informationexchangeto/fromasubroutine

• Useregisters:Simplebutlimitedinnumber

• Alternative:useprocessorstack• Alsoforlocalvariables&registers



ISA65

2.7.3 Stack Frame• Topoftheprocessorstack• =>privateworkspaceforsubroutines

• Astackframeisallocatedonsubroutineentryanddeallocated onsubroutineexit• Aframepointer(FP)registerenablesaccesstoprivateworkspaceforcurrentsubroutine• Subroutinenesting:thestackframealsosavesreturnaddressandFPofeachcaller



ISA66

Fig. 2.20 Stack LayoutSP

(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor

calledsubroutineReturn address

localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)



ISA67

Call Process (re: Fig. 2.20)1. Callingprogrampushes4parameters2. ThenCallinstructionexecuted• =>returnaddressonstack(↑SP)

Subroutine:3. FPisaGPregisterandsavedonstackby

a. MoveFP,-(SP)b. MoveSP,FP;↑SP=↑FP=old[FP]

4. Allocatelocalvariablesspacea. Subtract #12,SP

5. UseR2,R1sosaveonstack;↑SP=old[R1]



ISA68

Return Process (re: Fig. 2.20)• BeforeReturnfromsubroutine,Callee:

1. PopR1,R22. Add#12,SP;removelocalvariables3. Popold[FP]backtoFP

;↑SP=returnaddress• AfterReturn,Caller:

1. Popparameters;↑SP=oldTOS



ISA69

Fig. 2.20 Stack Layout-CallSP

(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack) CC-0

CC=Caller CallSC=Sub Call



ISA70


(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)

CC-1CC=Caller CallSC=Sub Call



ISA71


(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)

C-Call




ISA72


(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)

SC-3a




ISA73


(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)

SC-3b


SC-3b



ISA74


(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)

SC-4a


SC-3b



ISA75


(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)

SC-5


SC-3b



ISA76

Fig. 2.20 Stack Layout-ReturnSP

(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)

SR-1

SR=Caller RetCR=Sub Ret

SC-3b



ISA77


(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)

SR-2


SC-3b



ISA78


(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)


SR-3SC-3b



ISA79


(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack)


S-RET



ISA80


(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor


localvar3

localvar2

localvar1

saved [FP]

Old TOS

param2

param1

param3

param4

(top-of-stack) CR-1SR=Caller RetCR=Sub Ret



ISA81

Nested Subroutines Stack Frames

FP

FP

[FP] from SUB1

2164

Stackframe

forfirst

subroutine

[R0] from Main

param3

[R3] from Main

[R2] from Main

[R1] from Main

Old TOS

2012

[FP] from Main

param1

param2

[R0] from SUB1

[R1] from SUB1

Stackframefor

secondsubroutine



ISA82

Example: Nested Subroutines Program

Main program...

2000 Move PARAM2, (SP) Place parameterson stack.2004 Move PARAM1, (SP)2008 Call SUB12012 Move (SP),RESULT Store result.2016 Add #8,SP Restorestack level.2020 next instruction

...

––



ISA83

Nested Subroutines Sub-1

2100 SUB1 Move FP, (SP) Save frame pointer register.2104 Move SP,FP Load the framepointer.2108 MoveMultiple R0 R3, (SP) Save registers.2112 Move 8(FP),R0 Get first parameter.

Move 12(FP),R1 Get secondparameter....Move PARAM3, (SP) Placeaparameteron stack.

2160 Call SUB22164 Move (SP)+,R2 Pop SUB2 result into R2.

...Move R3,8(FP) Placeansweron stack.MoveMultiple (SP)+,R0 R3 Restoreregisters.Move (SP)+,FP Restoreframe pointer register.Return Return to Main program.

–

– –

–

–



ISA84

Nested Subroutines Sub-2

3000 SUB2 Move FP, (SP) Save frame pointer register.Move SP,FP Load the framepointer.MoveMultiple R0 R1, (SP) Save registersR0 and R1.Move 8(FP),R0 Get the parameter....Move R1,8(FP) PlaceSUB2result on stack.MoveMultiple (SP)+,R0 R1 RestoreregistersR0 and R1.Move (SP)+,FP Restoreframe pointer register.Return Return to Subroutine 1.

–

– –

–



ISA85

Nested Subroutines Stack Frames

FP

FP

[FP] from SUB1

2164

Stackframe

forfirst

subroutine

[R0] from Main

param3

[R3] from Main

[R2] from Main

[R1] from Main

Old TOS

2012

[FP] from Main

param1

param2

[R0] from SUB1

[R1] from SUB1

Stackframefor

secondsubroutine

2000 (SP)2004200821002104 (FP1)

2108

21128

2116

12

2156216030003004 (FP2)

3008

30128

30xx

30xx+430xx+830xx+122164

21yy

21yy+421yy+821yy+12/2012

2016



ISA86

Branch with Link



ISA87

Assignment: Stack Varieties• StackGrowth:•Ascending•Descending

• Stackpointer:• Fullstack• Emptystack



ISA88

Time and Space Tradeoff

0-CENG255 Ch2 17-v3 - ece.uvic.cakinli/ceng255/CENG255_Ch2_17-PartIV-revised.pdf · ISA 77 Fig....

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