============================= MemGuard IV.00 =========================== ======================================================================== Was written by Ralf Thanner in 100% assembly language! This release fixes some disadvantages encountered with the original MemWatch II program written by John Toebes. ================================ Purpose =============================== ======================================================================== MemGuard IV checks the first 100 longwords, in particular location $00000004, for random trashing. Discovering any change an Alert comes up giving you the choice to leave the vectors as they are or to restore their original contents. Unlike other tools of this kind MemGuard IV does not run as task, but rather links itself to the level 3 IRQ, checking the vectors each frame. Therefore virtually no processing time is wasted, no extra memory is used (very little actually, but below 1000 bytes - the original MemWatch II needed about 4000 bytes while running) and the checking takes place even while task-switching is forbidden. Furthermore most actions overriding the vector table are discovered almost instantly. MemGuard IV is NOT a virus killer but a usefull tool for 'C' Freaks. If an opening of a structure failed and you don't check this, your program starts writing random data to location $0. In most cases your Amiga will crash after this action. ================================= Usage ================================ ======================================================================== MemGuard IV can be started both from Workbench and CLI. The following options are recognized: "A" -> Activate MemGuard IV "Q" -> Terminate MemGuard IV "?" -> Displays a short list of instructions Note that these options are available from Workbench, too. A small menu will pop up and ask you for a selection. ============================= How it works ============================= ======================================================================== MemGuard IV allocates a chunk of memory, copies the checking routine into it, links it to the Vertical Blank interrupt and exits. As soon as an application trashes a low-memory vector an alert of the following form comes up: #====================================================================# # # # MemGuard IV.00 (C) 1990 by Ralf Thanner # # # # Adress: $xxxx OLD: xxxxxxxx NEW: xxxxxxx ASCII: 'xxxx' # # # # LEFT BUTTON TO CORRECT RIGHT BUTTON TO SAVE CHANGE # #====================================================================# -> 'ADRESS' displays the address having been overwritten. -> 'OLD' means the old value of the adress. -> 'NEW' gives the value it has received. -> 'ASCII' gives the ASCII text of the new value. - Pressing the left mouse button will restore the original contents of the trashed location. - Pressing the right mouse button will leave the location as it is. ================================= Author =============================== ======================================================================== MemGuard IV was written by Ralf Thanner using the Kuma Seka assembler, the original MemWatch idea was suggested from MemWatch II which had some substancial disadvantages. Ralf Thanner Ellerstrasse 83 D-4000 Duesseldorf 1 Federal Republic of Germany MemGuard IV (C) Copyright 1990 by Ralf Thanner Special thanks go to Olaf Barthel & Thorsten Hopf VERSIONS: ========= - MemGuard III ------------ Thought that this was the final version... No bug reports. - MemGuard III.a -------------- Because the MemGuard level3 IRQ part uses no message ports ( would slow down the everything ) I took 530(a6) as my `port'. The bad thing is that 530(a6) is the vertical blank frequency and programs which check this pointer had problems to interprete the value (PAL / NTSC). I had to switch to debug dat (70(a6)) which is currently not assigned to any particular function. Also added a cuter CLI-Interface. Shortened and improved the check routine: - now needs less than 896 bytes of memory. - takes only about 2-3 percent of processing time. (Memwatch II took about 50%) - MemGuard III.c -------------- As more and more Amiga users have an 68020 or 68030 which permit to relocate the IRQ vector table MemGuard was extended to check the exact location before actually redirecting the level 3 IRQ vector. - MemGuard III.d -------------- Extended the `trash' display. Shortened code and reprogrammed the checking routine: - Checking routine has become 924 bytes long and needs 8 raster lines. (MemGuard III.a needed 11 lines!!) - The exec.library vector is buffered internally to help MemGuard to survive a fatal change in $4. Thanks go to Holger Lubitz for this clever idea. - MemGuard IV.00 -------------- - Fat bug removed: the task running while MemGuard displayed the low memory change would freeze and finally hang (another nice feature of the task scheduler). - Integrated a low level task to display the alert. - Better Shell parameter check, will also handle tabs. =============================== MemGuard ================================ IMPORTANT NOTICE: This Program Is (c) Copyright By Ralf Thanner, But Can Be Freely Distributed, Providing That The Following Rules Are Respected. - No Change Is Made To The Program Nor To The Accompaning Documentation - The Package Is Always Distributed In Its Complete Form Consisting Of 2 Files: 'MemGuard' And 'MemGuard.Doc'. - Every Form Of Distribution Is Allowed And Encouraged, But No Fee Can Be Charged For This Program Except For, Possibly, The Cost Of Magnetic Media. By Copying, Distributing And/Or Using The Program You Indicate Your Acceptance Of The Above Rules. ============================================================================