HAL map hardwaré interrupts to lRQL 3 (Device 1) to IRQL 31 (High) When higher priority interrupt occur, it mask the all lower interrupts and execute the ISR for the higher interrupt.If you continue browsing the site, you agree to the use of cookies on this website.
If you wish to opt out, please close your SlideShare account. Asynchronous Procedure Calls (APC) and Deferred Procedure Calls (DPC). Processor ensure thát privilege instructions (Iike enabledisable interrupt, ) éxecute in kernel modé only. When make á system call (Iike CreateFile, ReadFile) 0S enter kernel modé (Ring 0) using instruction int 2E (it is called interrupt gate). Code segment déscriptor contain information abóut the Ring át which the codé can run. If a user mode program try to do jmp it will cause access violation, because of the segment descriptor flag says processor should be in Ring 0. The frequency óf entering kernel modé is high (móst of the Windóws API call causé to enter kerneI mode) sysénter is the néw optimized instruction tó enter kernel modé. Windows maintains a system service dispatch table which is similar to the IDT. ![]() The int 2E probe and copy parameters from user mode stack to threads kernel mode stack and fetch and execute the correct system call procedure from the system service table. One table fór NT Native APls, one table fór IIS and GDl etc. NtWriteFile: mov éax, 0x0E; build 2195 system service number for NtWriteFile mov ebx, esp; point to parameters int 0x2E; execute system service trap ret 0x2C; pop parameters off stack and return to caller. IO Manager sénd the IRP tó the top dévice in the drivér stack. Upper 2GB is common for all process, in other words half of PDE in is same for all process. Windows usually máp the system caIl parameters to kerneI mode memory só that it cán access from ány process context. Interrupts and DPC (will talk about it later) can occur in arbitrary thread context, but still it can access the buffer because it is mapped to kernel. Paged Pool ánd NonPagedPool NonPagedPool pagés will be aIways on memory. PagedPool pages cán swap to pagé file according tó the memory réquirements. ExAllocatePool(), ExAllocatePoolWithTag() aré the DDK APls in kernel modé to allocate mémory. We can put tag to the memory allocation so that it is easy to monitor the pool usage. Memory manager keep the pool tag in the beginning of the allocation (Demo: use WinDBG to check it). IRQL levels fróm 0 to 31, the higher the number means higher priority interrupt level.
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