IsDebuggerPresent函數的代碼如下：
64:A1 18000000 mov eax, dword ptr fs:[18] //fs寄存器指向了TEB
8B40 30 mov eax, dword ptr [eax+30]
0FB640 02 movzx eax, byte ptr [eax+2]
C3 retn
當運行完第一行代碼時，fs寄存器中的值爲TEB的地址，即爲fs指向了TEB，接下來看TEB的結構，TEB的結構可以通過windbg查看
kd> dt _teb
nt!_TEB
+0x000 NtTib : _NT_TIB
+0x01c EnvironmentPointer : Ptr32 Void
+0x020 ClientId : _CLIENT_ID //進程的pid
+0x028 ActiveRpcHandle : Ptr32 Void
+0x02c ThreadLocalStoragePointer : Ptr32 Void
+0x030 ProcessEnvironmentBlock : Ptr32 _PEB //進程PEB
+0x034 LastErrorValue : Uint4B
+0x038 CountOfOwnedCriticalSections : Uint4B
+0x03c CsrClientThread : Ptr32 Void
+0x040 Win32ThreadInfo : Ptr32 Void
+0x044 User32Reserved : [26] Uint4B
+0x0ac UserReserved : [5] Uint4B
+0x0c0 WOW32Reserved : Ptr32 Void
+0x0c4 CurrentLocale : Uint4B
+0x0c8 FpSoftwareStatusRegister : Uint4B
+0x0cc SystemReserved1 : [54] Ptr32 Void
+0x1a4 ExceptionCode : Int4B
+0x1a8 ActivationContextStack : _ACTIVATION_CONTEXT_STACK
+0x1bc SpareBytes1 : [24] UChar
+0x1d4 GdiTebBatch : _GDI_TEB_BATCH
+0x6b4 RealClientId : _CLIENT_ID
+0x6bc GdiCachedProcessHandle : Ptr32 Void
+0x6c0 GdiClientPID : Uint4B
+0x6c4 GdiClientTID : Uint4B
+0x6c8 GdiThreadLocalInfo : Ptr32 Void
+0x6cc Win32ClientInfo : [62] Uint4B
+0x7c4 glDispatchTable : [233] Ptr32 Void
+0xb68 glReserved1 : [29] Uint4B
在TEB結構中可以看出偏移量爲0x30h的字段爲ProcessEnvironmentBlock ，它是PEB結構，下面是PEB的結構。
0:023> dt ntdll!_PEB
+0x000 InheritedAddressSpace : UChar
+0x001 ReadImageFileExecOptions : UChar
+0x002 BeingDebugged : UChar
+0x003 BitField : UChar
+0x003 ImageUsesLargePages : Pos 0, 1 Bit
+0x003 IsProtectedProcess : Pos 1, 1 Bit
+0x003 IsImageDynamicallyRelocated : Pos 2, 1 Bit
+0x003 SkipPatchingUser32Forwarders : Pos 3, 1 Bit
+0x003 IsPackagedProcess : Pos 4, 1 Bit
+0x003 IsAppContainer : Pos 5, 1 Bit
+0x003 IsProtectedProcessLight : Pos 6, 1 Bit
+0x003 IsLongPathAwareProcess : Pos 7, 1 Bit
+0x004 Padding0 : [4] UChar
+0x008 Mutant : Ptr64 Void
+0x010 ImageBaseAddress : Ptr64 Void
+0x018 Ldr : Ptr64 _PEB_LDR_DATA
+0x020 ProcessParameters : Ptr64 _RTL_USER_PROCESS_PARAMETERS
+0x028 SubSystemData : Ptr64 Void
+0x030 ProcessHeap : Ptr64 Void
+0x038 FastPebLock : Ptr64 _RTL_CRITICAL_SECTION
+0x040 AtlThunkSListPtr : Ptr64 _SLIST_HEADER
+0x048 IFEOKey : Ptr64 Void
+0x050 CrossProcessFlags : Uint4B
+0x050 ProcessInJob : Pos 0, 1 Bit
+0x050 ProcessInitializing : Pos 1, 1 Bit
+0x050 ProcessUsingVEH : Pos 2, 1 Bit
+0x050 ProcessUsingVCH : Pos 3, 1 Bit
+0x050 ProcessUsingFTH : Pos 4, 1 Bit
+0x050 ProcessPreviouslyThrottled : Pos 5, 1 Bit
+0x050 ProcessCurrentlyThrottled : Pos 6, 1 Bit
+0x050 ProcessImagesHotPatched : Pos 7, 1 Bit
+0x050 ReservedBits0 : Pos 8, 24 Bits
+0x054 Padding1 : [4] UChar
+0x058 KernelCallbackTable : Ptr64 Void
+0x058 UserSharedInfoPtr : Ptr64 Void
+0x060 SystemReserved : Uint4B
+0x064 AtlThunkSListPtr32 : Uint4B
+0x068 ApiSetMap : Ptr64 Void
+0x070 TlsExpansionCounter : Uint4B
+0x074 Padding2 : [4] UChar
+0x078 TlsBitmap : Ptr64 Void
+0x080 TlsBitmapBits : [2] Uint4B
+0x088 ReadOnlySharedMemoryBase : Ptr64 Void
+0x090 SharedData : Ptr64 Void
+0x098 ReadOnlyStaticServerData : Ptr64 Ptr64 Void
+0x0a0 AnsiCodePageData : Ptr64 Void
+0x0a8 OemCodePageData : Ptr64 Void
+0x0b0 UnicodeCaseTableData : Ptr64 Void
+0x0b8 NumberOfProcessors : Uint4B
+0x0bc NtGlobalFlag : Uint4B
+0x0c0 CriticalSectionTimeout : _LARGE_INTEGER
+0x0c8 HeapSegmentReserve : Uint8B
+0x0d0 HeapSegmentCommit : Uint8B
+0x0d8 HeapDeCommitTotalFreeThreshold : Uint8B
+0x0e0 HeapDeCommitFreeBlockThreshold : Uint8B
+0x0e8 NumberOfHeaps : Uint4B
+0x0ec MaximumNumberOfHeaps : Uint4B
+0x0f0 ProcessHeaps : Ptr64 Ptr64 Void
+0x0f8 GdiSharedHandleTable : Ptr64 Void
+0x100 ProcessStarterHelper : Ptr64 Void
+0x108 GdiDCAttributeList : Uint4B
+0x10c Padding3 : [4] UChar
+0x110 LoaderLock : Ptr64 _RTL_CRITICAL_SECTION
+0x118 OSMajorVersion : Uint4B
+0x11c OSMinorVersion : Uint4B
+0x120 OSBuildNumber : Uint2B
+0x122 OSCSDVersion : Uint2B
+0x124 OSPlatformId : Uint4B
+0x128 ImageSubsystem : Uint4B
+0x12c ImageSubsystemMajorVersion : Uint4B
+0x130 ImageSubsystemMinorVersion : Uint4B
+0x134 Padding4 : [4] UChar
+0x138 ActiveProcessAffinityMask : Uint8B
+0x140 GdiHandleBuffer : [60] Uint4B
+0x230 PostProcessInitRoutine : Ptr64 void
+0x238 TlsExpansionBitmap : Ptr64 Void
+0x240 TlsExpansionBitmapBits : [32] Uint4B
+0x2c0 SessionId : Uint4B
+0x2c4 Padding5 : [4] UChar
+0x2c8 AppCompatFlags : _ULARGE_INTEGER
+0x2d0 AppCompatFlagsUser : _ULARGE_INTEGER
+0x2d8 pShimData : Ptr64 Void
+0x2e0 AppCompatInfo : Ptr64 Void
+0x2e8 CSDVersion : _UNICODE_STRING
+0x2f8 ActivationContextData : Ptr64 _ACTIVATION_CONTEXT_DATA
+0x300 ProcessAssemblyStorageMap : Ptr64 _ASSEMBLY_STORAGE_MAP
+0x308 SystemDefaultActivationContextData : Ptr64 _ACTIVATION_CONTEXT_DATA
+0x310 SystemAssemblyStorageMap : Ptr64 _ASSEMBLY_STORAGE_MAP
+0x318 MinimumStackCommit : Uint8B
+0x320 SparePointers : [4] Ptr64 Void
+0x340 SpareUlongs : [5] Uint4B
+0x358 WerRegistrationData : Ptr64 Void
+0x360 WerShipAssertPtr : Ptr64 Void
+0x368 pUnused : Ptr64 Void
+0x370 pImageHeaderHash : Ptr64 Void
+0x378 TracingFlags : Uint4B
+0x378 HeapTracingEnabled : Pos 0, 1 Bit
+0x378 CritSecTracingEnabled : Pos 1, 1 Bit
+0x378 LibLoaderTracingEnabled : Pos 2, 1 Bit
+0x378 SpareTracingBits : Pos 3, 29 Bits
+0x37c Padding6 : [4] UChar
+0x380 CsrServerReadOnlySharedMemoryBase : Uint8B
+0x388 TppWorkerpListLock : Uint8B
+0x390 TppWorkerpList : _LIST_ENTRY
+0x3a0 WaitOnAddressHashTable : [128] Ptr64 Void
+0x7a0 TelemetryCoverageHeader : Ptr64 Void
+0x7a8 CloudFileFlags : Uint4B
+0x7ac CloudFileDiagFlags : Uint4B
+0x7b0 PlaceholderCompatibilityMode : Char
+0x7b1 PlaceholderCompatibilityModeReserved : [7] Char
+0x7b8 LeapSecondData : Ptr64 _LEAP_SECOND_DATA
+0x7c0 LeapSecondFlags : Uint4B
+0x7c0 SixtySecondEnabled : Pos 0, 1 Bit
+0x7c0 Reserved : Pos 1, 31 Bits
+0x7c4 NtGlobalFlag2 : Uint4B
當運行完第二行代碼時，eax指向了PEB結構，運行完第三行代碼時，eax裝有BeingDebugged的值，當進程處於調式狀態時，BeingDebugged字段的值爲1，否則爲0。所以IsDebuggerPresent可以檢測進程是否處於調式狀態。