Windows teb thread

The data segment is used by most memory-access instructions, and the extra segment is used by the block operation instructions. We can use them for anything! On the , Windows uses the fs segment register to access a small block of memory that is associated with each thread, known as the Thread Environment Block, or TEB. To access memory relative to a specific segment register, you prefix the segment register and a colon to the memory reference.

All the other architectures use tables generated at compile time, so that there is no runtime penalty. Comments are closed. I wrote a book Ground rules Disclaimers and such My necktie's Twitter. February 3rd, It is not known what version 5. The first system reservation and its two spares was originally followed by a highly variable region that seems better to present version by version. Although the Win32ThreadInfo in version 3. This is the same structure that version 3.

The DbgSsReserved array supports the thread as a debugger of other processes. The early implementation—before version 5. The first of the handles is to a semaphore to wait on for notification that data is available from the port, the second is to the port. By version 3. The space they occupied became explicitly spare as SpareBytes1. This soon changed, however. At first, this just returned almost all the bytes of the ActivationContextStack to being spare.

Except that Windows Vista defined a member at the end, these spare bytes remained spare until Windows 10 put some to use for the instrumentation callback that can be set through the ProcessInstrumentationCallback case of NtSetInformationProcess. Note that the members that are added for Windows 10 have a slightly different order for the different processors. The x86 builds keep all four members together, again carving them from the beginning of previously spare bytes, and leaving some still spare.

Space is tighter in the x64 builds, such that the single-byte InstrumentationCallbackDisabled only fits by squeezing into the alignment requirement after the older TxFsContext.

Space in roughly the middle of the TEB , after what was originally a large system reservation, seems to have been dedicated from the start to supporting GDI What GdiThreadLocalInfo points to in version 3.

The information is also pointed to from offset 0x0C in the 0xbyte structure that version 3. Yes, this was all very much in flux back then! No use is known of the GdiThreadLocalInfo in version 4. The collection of members at offset 0x06FC in versions 3. It seems at least plausible that the pointer at 0x in version 3.

In both versions, USER32 obtains the pointer from the server and both saves it to a global variable and then passes it to a called routine. See that this does not allow much safety when version 5. This move seems to have happened as some sort of exchange with the growing allowance for the Win32ClientInfo. The oldest versions yet known to me of either are from Windows NT 3. The glDispatchTable in version 3. The pointer that is later labelled glReserved2 appears to be unused in version 3.

As later versions introduced ever more functions to point to, the glDispatchTable apparently could not be expanded. No later version fills the reduced glDispatchTable. This is nowadays documented as a kernel export. In version 5. The StaticUnicodeString and its Buffer seem to be provided as a convenience for pretty much any API function that has temporary need of a pathname-sized buffer.

DLL from the very beginning to hold per-thread data in what symbol files from version 4. No use of the next four bytes is yet known in version 4. Version 5. The booleans do not all disappear, however. Version 6. It continues in version 6. The FreeStackOnTermination member does not continue to version 6. It was anyway a relic of an ancient defence during thread termination. Before version 5. How useful this can have been is unclear.

The kernel seems unlikely to need much of a user-mode stack, but version 5. The 4-byte union models accurately that what the kernel sets for the ideal processor in version 6. This has the merit of keeping an 8-bit IdealProcessor at the same offset since version 5. As late as version No use is yet known of Wx86Thread. Whatever it was for, and whenever it was first defined, it was anyway discarded when Windows got both bit and bit builds. The remaining additions for Windows Vista were all discarded immediately afterwards, such that the TEB shrinks for Windows 7.

This page was created on 30th April and was last modified on 23rd October Geoff Chappell. All rights reserved. Conditions apply. Feedback Consult. Access Code executing in user mode can easily find the TEB for the current thread. While working on. In this article, I would like to share some of the basics about Windows thread which may help you in understanding how operating system implements threads. There are three basic components of Windows thread:.

All of these three components together create Windows thread. I tried to explain all of them one by one below but before looking into these three components, let's have a brief introduction about Windows kernel and kernel objects as these are the most important part of Windows operating system. Kernel is the main component of any operating system. It is a bridge between applications and hardware. Kernel provides layer of abstraction through which application can interact with hardware. Kernel is the part of the operating system that loads first, and it remains in physical memory.

The kernel's primary function is to manage the computer's hardware and resources and allow other programs to run and use these resources. To know more about kernel, visit this link. Kernel needs to maintain lots of data about numerous resources such as processes, threads, files, etc. Each kernel object is simply a memory block allocated by the kernel and is accessible only to the kernel.

This memory block is a data structure whose members maintain information about the object. Some members security descriptor, usage count, and so on are same across all object types, but most data members are specific to the type of kernel object.

If you are curious to see the list of all the kernel object types, then you can use free WinObj tool from Sysinternals located here. First and very basic component of Windows thread is thread kernel object. For every thread in system, operating system create one thread kernel object. Operating systems use these thread kernel objects for managing and executing threads across the system.

The kernel object is also where the system keeps all the statistical information about the thread. Below are some of the important properties of thread kernel object. Each thread kernel object contains set of CPU registers, called the thread's context. The context reflects state of the CPU registers when the thread last executed. The instruction pointer and stack pointer registers are the two most important registers in the threads context. A stack pointer is a register that stores the starting memory address of the stack frame of the current function executing inside the thread.

Instruction pointer points to the current instruction that need to be executed by the CPU. Operating system use kernel object context information while performing thread context switching. Context switch is the process of storing and restoring the state context of a thread so that execution can be resumed from the same point at a later time. Below mentioned table displays some of other important information held in thread kernel object about the thread.

The second basic component of a thread is stack.