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It is possible to break at the earliest part of Windows boot via the ENABLEJTAGBREAK facility made available within bootmgfw!BlBdWaitForJtagHwDebugger. In this article, thereโ€™s a short description and video whereby Iโ€™ve collected Intel Processor Trace as the target boots from early Windows to the first SMM entry; and then used AI to analyze it. The results are outstanding.ย 
JTAG can be used to explore the behavior of interrupt dispatching internals in a new way. This article describes the functionality of the Interrupt Descriptor Table (IDT) as an Intel target is booted from the reset vector, through UEFI, and into Windows.
In my prior two articles, I demonstrated the use of JTAG to set breakpoints inside SMM that survive Entry and Exit, and how to use Last Branch Record (LBR) trace to do dynamic analysis. In this blog, I show how to set up a visual view of SMRAM that updates dynamically as SMIs are hit.
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