cse351: memory, data, & addressing i · l02: memory & data i cse351, winter 2017 hardware:...

L02: Memory & Data I CSE351, Winter 2017

CSE351:Memory,Data,&AddressingICSE351Winter2017

http://xkcd.com/138/

Administrivia

v Start-of-Coursesurveyduetomorrowat5pmv Lab0dueMondayat5pm

§ Whotriedit?

v ConsidertakingCSE391(SystemandSoftwaretools)

v Allcoursematerialscanbefoundonthewebsite§ Calendarlinkfixed,subscribetoit!§ Sectionmaterialssidebar§ Readings:trytodothembeforeclass§ Slidespostedweekendbeforeclasses.Inksaved.§ Book:Sorry,reallyneed3rd edition.

Roadmap

car *c = malloc(sizeof(car));c->miles = 100;c->gals = 17;float mpg = get_mpg(c);free(c);

Car c = new Car();c.setMiles(100);c.setGals(17);float mpg =

c.getMPG();

get_mpg:pushq %rbpmovq %rsp, %rbp...popq %rbpret

Java:C:

Assembly language:

Machine code:

01110100000110001000110100000100000000101000100111000010110000011111101000011111

Computer system:

Memory & dataIntegers & floatsMachine code & Cx86 assemblyProcedures & stacksArrays & structsMemory & cachesProcessesVirtual memoryMemory allocationJava vs. C

Hardware:LogicalView

CPU Memory

Disks Net USB Etc.

Hardware:PhysicalView

CPU(emptyslot)

USB…

I/Ocontroller

StorageconnectionsMemory

Hardware:351View (version0)

v CPUexecutesinstructions;memorystoresdatav Toexecuteaninstruction,theCPUmust:

§ fetchaninstruction;§ fetchthedatausedbytheinstruction;and,finally,§ executetheinstructiononthedata…§ whichmayresultinwritingdatabacktomemory

Memory

instructions

v TheCPUholdsinstructionstemporarilyintheinstructioncachev TheCPUholdsdatatemporarilyinafixednumberofregistersv Instructionandoperandfetchingishardware-controlledv Datamovementisprogrammer-controlled(inassembly)v We’lllearnabouttheinstructionstheCPUexecutes–

takeCSE/EE470tofindouthowitactuallyexecutesthem 7

Memory

instructions

take470…

registers

i-cache

Memory

instructions

take470…

registers

i-cache

v TheCPUholdsinstructionstemporarilyintheinstructioncachev TheCPUholdsdatatemporarilyinafixednumberofregistersv Instructionandoperandfetchingishardware-controlledv Datamovementisprogrammer-controlled(inassembly)v We’lllearnabouttheinstructionstheCPUexecutes–

takeCSE/EE470tofindouthowitactuallyexecutesthem

Howaredataandinstructionsrepresented?

Howdoesaprogramfinditsdatainmemory?

Memory,Data,andAddressing

v Representinginformationasbitsandbytesv Organizingandaddressingdatainmemoryv ManipulatingdatainmemoryusingC

Question1:

Memory

instructions

take470…

registers

i-cache

Howaredataandinstructionsrepresented?

BinaryRepresentations

v Base2numberrepresentation§ Abase2digit(0or1)iscalledabit§ Represent35110 as00000001010111112 or1010111112

v Why?

Leadingzeros

BinaryRepresentations

v Base2numberrepresentation§ Abase2digit(0or1)iscalledabit§ Represent35110 as00000001010111112 or1010111112

v Electronicimplementation§ Easytostorewithbi-stableelements§ Reliablytransmittedonnoisyandinaccuratewires

0.0V0.5V

2.8V3.3V

Leadingzeros

Review:NumberBases

v Keyterminology: digit(d)andbase(B)§ InbaseB,eachdigitisoneofBpossiblesymbols

v Valueof𝑖-th digitis𝑑×𝐵% where𝑖 startsat0andincreasesfromrighttoleft§ n digitnumberdn-1dn-2 ...d1d0§ value=dn-1´Bn-1+dn-2´Bn-2 +...+d1´B1 +d0´B0

§ Inafixed-width representation,left-mostdigitiscalledthemost-significant andtheright-mostdigitiscalledtheleast-significant

v Notation: Baseisindicatedusingeitheraprefixorasubscript

DescribingByte Valuesv Binary(000000002 – 111111112)

§ Byte=8bits(binarydigits)

v Decimal(010 – 25510)v 10isnotapowerof2L.

0 0 1 0 1 1 0 10*27 0*26 1*25 0*24 1*23 1*22 0*21 1*20

32 8 4 1 = 4510

LSBMSB

DescribingByte Valuesv Binary(000000002 – 111111112)

§ Byte=8bits(binarydigits)

v Decimal(010 – 25510)v Hexadecimal(0016 – FF16)

§ Byte=2hexadecimal(or“hex”orbase16)digits§ Base16numberrepresentation§ Usecharacters‘0’to‘9’and‘A’to‘F’§ WriteFA1D37B16 intheClanguage

• as0xFA1D37B or0xfa1d37b

v Moreonspecificdatatypeslater…15

0 0 00001 1 00012 2 00103 3 00114 4 01005 5 01016 6 01107 7 01118 8 10009 9 1001A 10 1010B 11 1011C 12 1100D 13 1101E 14 1110F 15 1111

0 0 1 0 1 1 0 10*27 0*26 1*25 0*24 1*23 1*22 0*21 1*20

32 8 4 1 = 4510

LSBMSB

Question2:

Memory

instructions

take470…

registers

i-cache

Howdoesaprogramfinditsdatainmemory?

Byte-OrientedMemoryOrganization

v Conceptually,memoryisasingle,largearrayofbytes,eachwithauniqueaddress (index)

v Thevalueofeachbyteinmemorycanbereadandwrittenv Programsrefertobytesinmemorybytheiraddresses

§ Domainofpossibleaddresses=addressspace

v Butnotallvalues(e.g.,351)fitinasinglebyte…§ Storeaddressesto“remember”whereotherdataisinmemory§ Howmuchmemorycanweaddresswith1-byte(8-bit)addresses?

v Manyoperationsactuallyusemulti-bytevalues

• • •

MachineWords

v Wordsize=addresssize=registersizev Wordsizeboundsthesizeoftheaddressspaceandmemory§ wordsize=𝑤 bits→ 2𝑤 addresses

v Currentx86systemsuse64-bit(8-byte)words§ Potentialaddressspace:𝟐𝟔𝟒 addresses264 bytes» 1.8x1019 bytes=18billionbillionbytes=18EB(exabytes)=16EiB (exbibytes)

§ Actualphysicaladdressspace:48bits

Aside:UnitsandPrefixes

v Herefocusingonlargenumbers(exponents>0)v Notethat103 ≈210

v SIprefixesareambiguousifbase10or2v IECprefixesareunambiguouslybase2

Word-OrientedMemoryOrganizationv Addressesspecify

locationsofbytesinmemory§ Addressofword

=addressoffirstbyteinword§ Addressesofsuccessivewords

differbywordsize(inbytes):e.g.,4(32-bit)or8(64-bit)

§ Addressofword0,1,…10?

0x000x010x020x030x040x050x060x070x080x090x0A0x0B

32-bitWords

0x0C0x0D0x0E0x0F

64-bitWords

Addr=??

Addr.(hex)

Word-OrientedMemoryOrganizationv Addressesstillspecify

locationsofbytes inmemory§ Addressofword

=addressoffirstbyteinword§ Addressesofsuccessivewords

differbywordsize(inbytes):e.g.,4(32-bit)or8(64-bit)

§ Addressofword0,1,…10?§ Alignment

32-bitWords

Bytes64-bitWords

Addr=??

0x000x010x020x030x040x050x060x070x080x090x0A0x0B0x0C0x0D0x0E0x0F

Addr.(hex)

APictureofMemory(64-bitview)

v A“64-bit(8-byte)word-aligned”view ofmemory:§ Inthistypeofpicture,eachrowiscomposedof8bytes§ Eachcellisabyte§ A64-bitpointerwillfitononerow

0x000x0x0x0x0x0x0x0x0x

0x04 0x05 0x06 0x070x00 0x01 0x02 0x03

oneword

Address

APictureofMemory(64-bitview)

v A“64-bit(8-byte)word-aligned”view ofmemory:§ Inthistypeofpicture,eachrowiscomposedof8bytes§ Eachcellisabyte§ A64-bitpointerwillfitononerow

0x0D 0x0E 0x0F0x0C

0x000x080x100x180x200x280x300x380x400x48

Address

0x09 0x0A 0x0B0x08

oneword

0x04 0x05 0x06 0x070x00 0x01 0x02 0x03

AddressesandPointers

v Anaddress isalocationinmemoryv Apointer isadataobjectthatholdsanaddress

§ Addresscanpointtoany data

v Value351storedataddress0x08§ 35110 =15F16=0x0000015F

v Pointerstoredat0x38 pointstoaddress0x08

0x000x080x100x180x200x280x300x380x400x48

64-bit example(pointers are 64-bits wide)

Address

00 00 00 00 00 00 01 5F

00 00 00 00 00 00 00 08

AddressesandPointers

v Anaddress isalocationinmemoryv Apointer isadataobjectthatholdsanaddress

§ Addresscanpointtoany data

v Pointerstoredat0x48 pointstoaddress0x38§ Pointertoapointer!

v Isthedatastoredat0x08 apointer?§ Couldbe,dependingonhowyouuseit

0x000x080x100x180x200x280x300x380x400x48

64-bit example(pointers are 64-bits wide)

Address

00 00 00 00 00 00 01 5F

00 00 00 00 00 00 00 08

00 00 00 00 00 00 00 38

v Sizesofdatatypes(inbytes)

DataRepresentations

26Touse“bool”inC,youmust#include <stdbool.h>

Java Data Type C Data Type 32-bit (old) x86-64boolean bool 1 1byte char 1 1char 2 2short short int 2 2int int 4 4float float 4 4

long int 4 8double double 8 8long long 8 8

long double 8 16(reference) pointer * 4 8(reference) pointer * 4 8

address size = word size

MoreonMemoryAlignmentinx86-64

v Forgoodmemorysystemperformance,Intelrecommendsdatabealigned§ Howeverthex86-64hardwarewillworkcorrectlyregardlessofalignmentofdata

§ Designchoice:x86-64instructionsarevariable byteslong

v Aligned: Primitiveobjectof𝐾 bytesmusthaveanaddressthatisamultipleof𝐾§ Moreaboutalignmentlaterinthecourse

𝐾 Type1 char2 short4 int, float8 long, double, pointers

ByteOrdering

v Howshouldbyteswithinawordbeorderedinmemory?§ Example:storethe4-byte(32-bit)int:0x a1 b2 c3 d4

v Byconvention,orderingofbytescalledendianness§ Thetwooptionsarebig-endianandlittle-endian§ BasedonGulliver’sTravels:tribescuteggsondifferentsides(big,little)

ByteOrdering

v Big-endian(SPARC,z/Architecture)§ Leastsignificantbytehashighestaddress

v Little-endian(x86,x86-64)§ Leastsignificantbytehaslowestaddress

v Bi-endian(ARM,PowerPC)§ Endiannesscanbespecifiedasbigorlittle

v Example: 4-bytedata0xa1b2c3d4ataddress0x100

0x100 0x101 0x102 0x103

01 23 45 670x100 0x101 0x102 0x103

67 45 23 01

Big Endian

Little Endian

a1 b2 c3 d4

d4 c3 b2 a1

ByteOrderingExamples

Decimal: 12345Binary: 0011 0000 0011 1001Hex: 3 0 3 9

39300000

IA32,x86-64(littleendian)

00000000

39300000

x86-64

39300000

SPARC(bigendian)

32-bitSPARC

64-bitSPARC

00000000

int x = 12345;// or x = 0x3039;

long int y = 12345;// or y = 0x3039;

(Along int isthesizeofaword)

0x000x010x020x03

0x000x010x020x030x040x050x060x07

Endianness

v Oftenprogrammercanignoreendiannessbecauseitishandledforyou§ Byteswiredintocorrectplacewhenreadingorstoringfrommemory(hardware)

§ Compilerandassemblergeneratecorrectbehavior(software)

v Endiannessstillshowsup:§ Logicalissues:accessingdifferentamountofdatathanhowyoustoredit(e.g.storeint,accessbyteasachar)

§ Whenrunningdownmemoryerrors,needtoknowexactvalues

§ Manualtranslationtoandfrommachinecode(in351)31

ReadingByte-ReversedListingsv Disassembly

§ Takebinarymachinecodeandgenerateanassemblycodeversion§ Doesthereverseoftheassembler

v Exampleinstructioninmemory§ addvalue0x12abtoregister‘ebx’(aspeciallocationintheCPU)

Address InstructionCode AssemblyRendition8048366: 81c3ab120000 add$0x12ab,%ebx

32-bit example

Decipheringnumbers

ReadingByte-ReversedListingsv Disassembly

§ Takebinarymachinecodeandgenerateanassemblycodeversion§ Doesthereverseoftheassembler

v Exampleinstructioninmemory§ addvalue0x12abtoregister‘ebx’(aspeciallocationintheCPU)

Address InstructionCode AssemblyRendition8048366: 81c3ab 120000 add$0x12ab,%ebx

Decipheringnumbersn Value: 0x12ab

n Padto32bits: 0x000012ab

n Splitintobytes: 00 00 12 ab

n Reverse(little-endian): ab 12 00 00

32-bit example

Question:

v Westorethevalue0x 00 01 02 03 asaword ataddress0x100 andthengetback0x00 whenwereadabyte ataddress0x102

v Whatmachinesetupareweusing?

32-bit,big-endian(A)32-bit,little-endian(B)64-bit,big-endian(C)

Summary

v Memoryisalong,byte-addressed array§ Wordsizeboundsthesizeoftheaddressspaceandmemory§ Differentdatatypesusedifferentnumberofbytes§ Addressofchunkofmemorygivenbyaddressoflowestbyteinchunk

§ Objectof𝐾 bytesisaligned ifithasanaddressthatisamultipleof𝐾

v IECprefixesrefertopowersof2-.

v Pointersaredataobjectsthatholdsaddressesv Endiannessdeterminesstorageorderformulti-byteobjects

cse351: memory, data, & addressing i · l02: memory & data i cse351, winter 2017 hardware:...

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