MSILVosSpec.docx

MSILVosSpec.docx

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MSILVosSpec

CommonLanguageRuntime

TechnicalOverviewof

theCommonLanguageRuntime

Version1.4Beta1

Copyright2000MicrosoftCorporation.Allrightsreserved.

Lastupdated:

10/15/186:

20PM

Contacts:

jsmiller,lisasu

TableofContents

1OverviewoftheCommonLanguageRuntime7

1.1ProblemsAddressed8

1.2RelationshiptoTypeSafety9

1.3RelationshiptoManagedMetadata-drivenExecution10

1.3.1ManagedCode10

1.3.2ManagedData11

1.4RelationshiptoUnmanagedCOM12

1.5IntroductiontotheCommonLanguageSpecification（CLS）12

1.6Summary14

2TypeSystem16

2.1RelationshiptoObject-OrientedProgramming17

2.2ValuesandTypes18

2.2.1ValueTypesandReferenceTypes18

2.2.2Built-InTypes18

2.2.3Classes,InterfacesandObjects19

2.2.4BoxingandUnboxingofValues20

2.2.5IdentityandEqualityofValues20

2.2.5.1Identity21

2.2.5.2Equality21

2.3Locations22

2.3.1AssignmentCompatibleLocations22

2.3.2Coercion22

2.3.3Casting22

2.4TypeMembers24

2.4.1Fields,ArrayElements,andValues24

2.4.2Methods24

2.4.3StaticFieldsandStaticMethods25

2.4.4VirtualMethods25

2.5Naming26

2.5.1ValidNames26

2.5.2AssembliesandScoping26

2.5.3Visibility,Accessibility,andSecurity28

2.5.3.1VisibilityofTypes29

2.5.3.2AccessibilityofMembers29

2.5.3.3SecurityPermissions30

2.5.3.4NestedTypes30

2.6Contracts32

2.6.1Signatures33

2.6.1.1TypeSignatures33

2.6.1.2LocationSignatures33

2.6.1.3LocalSignatures34

2.6.1.4ParameterSignatures35

2.6.1.5MethodSignatures35

2.7AssignmentCompatibility37

2.8TypeSafetyandVerification38

2.9TypeDefiners39

2.9.1ArrayTypes39

2.9.2PointerTypes40

2.9.3InterfaceTypeDefinition41

2.9.4ClassTypeDefinition42

2.9.5ObjectTypeDefinitions43

2.9.5.1ScopeandVisibility43

2.9.5.2Concreteness43

2.9.5.3TypeMembers44

2.9.5.4SupportingInterfaceContracts44

2.9.5.5SupportingClassContracts45

2.9.5.6Constructors45

2.9.5.7Finalizers46

2.9.6ValueTypeDefinition46

2.9.7TypeInheritance47

2.9.8ObjectTypeInheritance47

2.9.9ValueTypeInheritance47

2.9.10InterfaceTypeInheritance47

2.10MemberInheritance49

2.10.1FieldInheritance49

2.10.2MethodInheritance49

2.10.3PropertyandEventInheritance49

2.10.4Hiding,Overriding,andLayout49

2.11MemberDefinitions52

2.11.1MethodDefinitions52

2.11.2FieldDefinitions52

2.11.3PropertyDefinitions53

2.11.4EventDefinitions54

2.11.5NestedTypeDefinitions54

3CLRMetadata56

3.1ComponentsandAssemblies57

3.2AccessingMetadata58

3.2.1MetadataTokens58

3.2.2MemberSignaturesinMetadata59

3.3UnmanagedCOMandUnmanagedCode60

3.4MethodImplementationMetadata61

3.5ClassLayout62

3.6Assemblies:

NameScopesforTypes63

3.7MetadataExtensibility65

3.8Globals,Imports,andExports67

3.9ScopedStatics68

4CommonLanguageSpecification70

4.1MarkingItemsasCLS-Compliant70

4.2Identifiers71

4.3Overloading71

4.4OperatorOverloading73

4.4.1UnaryOperators73

4.4.2BinaryOperators73

4.4.3ConversionOperators75

4.5NamingPatterns75

4.6CollectedCLSRules76

5TheVirtualExecutionSystem（VES）80

5.1MicrosoftIntermediateLanguage（MSIL）81

5.2LoadingManagedCode83

5.3ConversionofMSILintoNativeCode84

5.4VerificationofImplementationCode85

5.5ServicesBasedonStackFormat85

5.6SecurityServices87

5.7ProfilingandDebuggingServices88

5.8Delegates90

5.9Proxies,Contexts,andRemoting90

6Index93

OverviewoftheCommonLanguageRuntime

Thisdocumentservesasahigh-leveltechnicalintroductiontothearchitectureoftheCommonLanguageRuntime（CLR）,partofthe.NETFramework.Whereappropriate,thisdocumentprovidespointerstomoredetailedinformationcontainedinotherdocuments.Atthecenteroftheruntimeisasingletypesystem,theCommonTypeSystem（CTS）,whichissharedbycompilers,tools,andtheruntimeitself.Itisthemodelthatdefinestherulestheruntimefollowswhendeclaring,using,andmanagingtypes.TheCTSestablishesaframeworkthatenablescross-languageintegration,typesafety,andhighperformancecodeexecution.ThisdocumentdescribesthearchitectureofCLRbydescribingtheCTSanditsimplementationbytheruntime.

Thefollowingfourareasarecoveredinthisdocument:

TheCommonTypeSystem.TheCommonTypeSystem（CTS）providesarichtypesystemthatsupportsthetypesandoperationsfoundinmanyprogramminglanguages.TheCommonTypeSystemisintendedtosupportthecompleteimplementationofawiderangeofprogramminglanguages.

Metadata.TheCLRusesmetadatatodescribeandreferencethetypesdefinedbytheCommonTypeSystem.Metadatacanbestored（“persisted”）inawaythatisindependentofanyparticularprogramminglanguage.Thus,metadataprovidesacommoninterchangemechanismforusebetweentoolsthatmanipulateprograms（compilers,debuggers,etc.）aswellasbetweenthesetoolsandtheVirtualExecutionSystem.

TheCommonLanguageSpecification.WhilenotstrictlypartoftheCTS,theCommonLanguageSpecificationisanagreementbetweenlanguagedesignersandframework（classlibrary）designers.ItspecifiesasubsetoftheCTSTypeSystemandasetofusageconventions.LanguagesprovidetheirusersthegreatestabilitytoaccessframeworksbyimplementingatleastthosepartsoftheCTSthatarepartoftheCLS.Similarly,frameworkscanbemostwidelyusediftheirpubliclyexposedaspects（classes,interfaces,methods,fields,etc.）useonlytypesthatarepartoftheCLSandadheretotheCLSconventions.

TheVirtualExecutionSystem.TheVirtualExecutionSystem（VES）implementsandenforcestheCTSmodel.TheVESisresponsibleforloadingandrunningprogramswrittenfortheCLR.Itprovidestheservicesneededtoexecutemanagedcodeanddata,usingthemetadatatoconnectseparatelygeneratedmodulestogetheratruntime（latebinding）.

Together,theseaspectsoftheCLRformaunifyingframeworkfordesigning,developing,deploying,andexecutingdistributedcomponentsandapplications.TheappropriatesubsetoftheCommonTypeSystemisavailablefromeachprogramminglanguagethattargetstheCLR.Language-basedtoolscommunicatewitheachotherandwiththeVirtualExecutionSystemusingmetadatatodefineandreferencethetypesusedtoconstructtheapplication.TheVirtualExecutionSystemusesthemetadatatocreateinstancesofthetypesasneededandtoprovidedatatypeinformationtootherpartsoftheinfrastructure（suchasremotingservices,assemblydownloading,security,etc.）.

ProblemsAddressed

TheCommonTypeSystemaddressesanumberofissuesthathavecomplicatedthecreationanddeploymentofdistributedapplications:

Similarandbutsubtlyincompatibletypes-Dates,Times,Integers,SQLnullabletype,etc.

Limitedcodereuse-Cannotimportatypefromadifferentlanguageandtreatitthesameastypesdefineddirectlyinthelanguage.

Non-uniformobjectmodels–Differingwaysofdealingwithevents,dynamicbehaviors,persistence,properties,exceptions,etc.

TheCTSabstractsandsimplifiesthedetailsofthelanguage/toolthatmustbeknownbeforeaservicecanbebuilt.Byprovidingacommonframework,itallowstheruntimeandassociatedservicestoautomatemuchoftheworkthatisperformedmanuallytoday.Thecommonframeworkrepairsthefollowingweaknessesintoday’sinfrastructure:

Nocommonexecutionmodel-Nouniformwaytoinspectthestateofanexecutingprogram.Crucialforcodeaccesssecurity,enablesdeclarativeruntimeservices,andsimplifiestoolslikeprofilers.

Brittlebindingmechanisms–Allthethingsthatleadto“DLLhell”andthegeneralversioningproblemsthatarisefromsoftwareevolution.

Inshort,toolittleisknownaboutaprogramafteritiscompiled.TheCLRaddressesthisproblembyproviding:

aCommonType,

ameansofpersistinginformationabouttypesalongwiththecomponentsthatusethem（metadata）,

aspecificationofthesubsetoftypesthathavebroadreachacrossprogramminglanguages,and

ameansofbuildinginstancesgiventypedescriptions（theVirtualExecutionSystem）.

RelationshiptoTypeSafety

Typesafetyisusuallydiscussedintermsofwhatitdoes,e.g.guaranteeingencapsulationbetweendifferentobjects,orintermsofwhatitprevents,e.g.memorycorruptionbywritingwhereoneshouldn’t.However,fromthepointofviewoftheCommonTypeSystem,typesafetyisaboutguaranteeing:

Referencesarewhattheysaytheyare-Everyreferenceistypedandthethingreferenced,thedefinition,alsohasatype,andtheyarecompatibleinastrictsense.

Identitiesarewhotheysaytheyare-Thereisnowaytocorruptorspoofanobject,andbyimplicationauserorsecuritydomain.Theaccesstoanobjectisthroughaccessiblefunctionsandfields.Anobjectcanstillbepoorlydesigned.Thekeyisthatalocalanalysisoftheobjectandthethingsituses,asopposedtoaglobalanalysisofallusesofanobject,issufficienttounderstandthevulnerabilities

Onlyappropriateoperationscanbeinvoked–Thereferencetypedefinestheaccessiblefunctionsandfields.Thisincludeslimitingvisibilitybasedonwherethereferenceis,e.g.protectedfieldsonlyvisibleinsubclasses

TheCommonTypeSystempromotestypesafetye.g.everythingistyped.Typesafetycanbeoptionallyenforced.Thehardproblemisdeterminingifanimplementationconformstoatypesafedeclaration.Sincethedeclarationsarecarriedalongasmetadatawiththecompiledformoftheprogram,acompilerfromMicrosoftIntermediateLanguage（MSIL）tonativecode（seeTypeSafetyandVerification）cantype-checktheimplementations.Whencoupledwithcodesigning,theissueisthenwhentot