Timeout for some demos An instructive look at how the

Timeout for some demos

• An instructive look at how the

• Linux Operating System

• sets up system data-structures

CPU’s ‘fetch-execute’ cycle

System registers and tables

‘activity.s’

• This is a ‘boot-time’ application program

• You assemble, link, install, and reboot

• It runs entirely in x86 ‘real-mode’

• It maintains an array of counters

• It ‘hooks’ all of the 256 interrupt-vectors

• Every interrupt-occurrence gets counted

• The counters are continuously displayed

‘activity.cpp’

• This is a Linux application program

• It’s similar to our previous demo ‘activity.s’

• It shows us all the interrupts which occur

• But it runs in ‘protected-mode’ at ring3

• So it can’t modify the IDT directly

• Instead it uses the services of an LKM

• The LKM source-file is called ‘activity.c’

‘mmake.cpp’

• This program makes it easy to compile an LKM for version 2.6 of the Linux kernel

• If your LKM is named ‘myLKM.c’, then you compile it using: $ mmake myLKM

• The result is a kernel object (‘myLKM.ko’)

• You install the kernel object with ‘insmod’, and you remove it with ‘rmmod’, like this:

• $ /sbin/insmod myLKM.ko
• $ /sbin/rmmod myLKM.ko

Overview of the LKM

Device-driver LKM

• Our ‘dram.c’ module provides services

• Lets applications ‘read’ physical memory

• Lets applications find the memory’s size

• Works with 32-bit Linux or 64-bit Linux

• SysAdmin must setup device-file node

‘showgdt.cpp’

• This application shows the Linux GDT

• It uses services of the ‘dram.ko’ driver

• You can try it in Kudlick classroom

• You can try it on your ‘anchor’ machine

‘showidt.cpp’

• This application shows the Linux IDT

• It uses services of the ‘dram.ko’ driver

• You can try running it on ‘anchor’ machine

• You will see all 256 IDT gate-descriptors!

• (But it’s designed only for 64-bit Linux)

pseudocode

• We wrote an algorithm-description (using pseudocode) for UART’s THRE interrupt when you want to implement ‘redirection’ of console output to a remote terminal via the serial null-modem cable

• We implemented our algorithm in a demo program (named ‘redirect.s’) which runs in 32-bit protected-mode

A ‘rapid prototype’ tool

• We wrote a ‘newapp64.cpp’

• It creates six pages of ‘boilerplate’ code for a boot-time assembly language application that will execute 64-bit code

• It includes ‘isrGPF’ (for debugging aid)

• We can use it to quickly create future demo programs that explore EM64T

In-class exercise

• Use the ‘newapp64’ tool to create a ‘test’ program that you will install and execute on an ‘anchor’ machine – but first insert into the 64-bit portion of the code some type of invalid instruction which will trigger a General Protection Exception – so you can see what debugging information gets displayed by the ‘isrGPF’ fault-handler