TweetFollow Us on Twitter

ShiftMod
Volume Number:3
Issue Number:9
Column Tag:Technical Note

ShiftMod Patch

By Mike Scanlin, San Diego, CA

Last week we were talking with an IBM freak about the differences between our Macs and his footrest, that is, PC. One of his complaints about the Mac was that you get upper case letters when both the shift key and caps lock key are down at the same time. He wanted to be able to type a lower case letter if the caps lock key was down by pressing the shift key. Then he could type sentences like “i WISH i HAD A mACINTOSH” without having to hold down the shift key the whole time. Well, Mac fans, fear not. Now the Mac can do this too. Say hello to Mr. ShiftMod.

All that is really needed is a tail patch to _GetNextEvent that checks if a keyDown or autoKey event occured while the caps lock and shift keys were held down. The only problem with implementing it is that because _GetNextEvent is a stack based trap (it gets its parameters from the stack) the patch requires a bit of self modifying code to get it to set things up correctly. While this example is trivial, the technique used here can be used to patch any stack based trap routine.

A tail patch is something that first calls the original trap and then does some post-processing before returning to the caller. If the original trap is not stack based, we can do a JSR OriginalTrap at the beginning of our patch, do our post-processing, and end with an RTS. However, if the original trap is stack based it will expect the stack to look a certain way when it gets called. By doing a JSR to it, we put a return address on top of the existing stack which, in effect, shifts all of the parameters by 4 bytes (relative to the top of the stack). The routine being called does not know about the extra return address and will use the wrong bytes as parameters.

The code listed here is an application, but it can be easily (via ResEdit) be made into an INIT resource and pasted into your system file. It installs itself in the system heap and hangs around as long as you don’t turn your Mac off. This code is useful if you want to install any event processing stuff that is global for all applications. For instance, you could call _Eject every time you detect a diskEvt and count how many times someone tries to insert a disk in a minute. Or you could do something semi-useful like adding a keyclick after keyDowns (how about a mouseclick on mouseDowns?) for debugging.

Now how about an IBM hacker writing a routine to make his machine return upper case letters when both the shift key and caps lock key are down? Is it even possible?

/* shiftMod.c    2 July 1987
 * 
 * by Mike Scanlin and Andy Voelker
 *
 * This program installs a tail patch on _GetNextEvent so
 * that the shift key toggles between upper and lower case
 * letters if the caps lock key is down.
 *
 * No toggle is done if the option and/or command key was
 * held down.
 */
 
#include“Asm.h”
#include“EventMgr.h”

#define whatOFFSET(EventRecord,what)
#define message  OFFSET(EventRecord,message)
#define modifiersOFFSET(EventRecord,modifiers)

#define GetNextEvent 0xA970
#define JMP 0x4EF9
#define memFullErr -108

main()
{
 asm  {
 move.l D3,-(SP)
 
/* set up the JMP instruction at the end of the patch */
 lea    @patchExit,A0
 move #JMP,(A0)

/* get the old trap address */
 move #GetNextEvent,D0
 _GetTrapAddress
 
/* set up the JMP instruction that calls the original trap */
 lea    @origTrap,A1
 move #JMP,(A1)+
 move.l A0,(A1)

/* get some space in the system heap */
 lea    @last,A0
 lea    @first,A1
 suba.l A1,A0
 move.l A0,D0
 move.l D0,D3  /* save for _BlockMove */
 _NewPtrSYS
 cmpi #memFullErr,D0
 beq.s  @noPatch
 move.l A0,-(SP) /* save for _BlockMove */

/* set the trap address to the space we just got in the
 * system heap
 */
 move #GetNextEvent,D0
 _SetTrapAddress
 
/* now move it into place */
 lea    @first,A0
 move.l (SP)+,A1
 move.l D3,D0
 _BlockMove
 
@noPatchmove.l (SP)+,D3
 rts

/* Here’s the new _GetNextEvent.  It calls the existing
 * _GetNextEvent and then checks if a keyDown or autoKey
 * event is being reported.
 */

 /* save original return address */
@first  lea @exitAddress,A0
 move.l (SP)+,(A0)

 /* save ptr to event record */
 lea    @eventPtr,A0
 move.l (SP),(A0)

 /* return to our routine */
 pea    @tailPatch

@origTrap nop    /* JMP to original trap */
 nop
 nop
 
@tailPatchlea    @eventPtr,A0
 move.l (A0),A0

 /* Is it a keyDown or autoKey? */
 move what(A0),D0
 cmpi #keyDown,D0
 beq.s  @isKeyDown
 cmpi #autoKey,D0
 bne.s  @patchExit

@isKeyDownmove modifiers(A0),D0
 andi   #shiftKey+alphaLock+optionKey
 +cmdKey,D0
 eori   #shiftKey+alphaLock,D0
 bne.s  @patchExit

 move.l message(A0),D0
 cmpi.b #’A’,D0
 bmi.s  @patchExit
 cmpi.b #’Z’,D0
 bgt.s  @patchExit
 addi.b #’a’-’A’,D0
 move.l D0,message(A0)

 /* return to original caller via long JMP */
@patchExitnop
@exitAddressnop
 nop


@eventPtr dc.l 0 /* storage for event record ptr */

@last
 }
}
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Ableton Live 9.7.1 - Record music using...
Ableton Live lets you create and record music on your Mac. Use digital instruments, pre-recorded sounds, and sampled loops to arrange, produce, and perform your music like never before. Ableton Live... Read more
FileZilla 3.23.0.2 - Fast and reliable F...
FileZilla (ported from Windows) is a fast and reliable FTP client and server with lots of useful features and an intuitive interface. Version 3.23.0.2: Bug Fixes and Minor Changes Speed up icon... Read more
Vivaldi 1.5.658.56 - An advanced browser...
Vivaldi is a browser for our friends. In 1994, two programmers started working on a web browser. Our idea was to make a really fast browser, capable of running on limited hardware, keeping in mind... Read more
Safari Technology Preview 10.1 - The new...
Safari Technology Preview contains the most recent additions and improvements to WebKit and the latest advances in Safari web technologies. And once installed, you will receive notifications of... Read more
TunnelBear 3.0.8 - Subscription-based pr...
TunnelBear is a subscription-based virtual private network (VPN) service and companion app, enabling you to browse the internet privately and securely. Features Browse privately - Secure your data... Read more
NeoFinder 7.0 - Catalog your external me...
NeoFinder (formerly CDFinder) rapidly organizes your data, either on external or internal disks, or any other volumes. It catalogs all your data, so you stay in control of your data archive or disk... Read more
Coda 2.6 - One-window Web development su...
Coda is a powerful Web editor that puts everything in one place. An editor. Terminal. CSS. Files. With Coda 2, we went beyond expectations. With loads of new, much-requested features, a few surprises... Read more
File Juicer 4.51 - Extract images, video...
File Juicer is a drag-and-drop can opener and data archaeologist. Its specialty is to find and extract images, video, audio, or text from files which are hard to open in other ways. In computer... Read more
PDFpenPro 8.3 - $124.95
PDFpenPro allows users to edit PDF's easily. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Create fillable forms and tables of content... Read more
PDFpen 8.3 - $74.95
PDFpen allows users to easily edit PDF's. Add text, images and signatures. Fill out PDF forms. Merge or split PDF documents. Reorder and delete pages. Even correct text and edit graphics! Features... Read more

Latest Forum Discussions

See All

Niantic teases new Pokémon announcement...
After rumors started swirling yesterday, it turns out there is an official Pokémon GO update on its way. We’ll find out what’s in store for us and our growing Pokémon collections tomorrow during the Starbucks event, but Niantic will be revealing... | Read more »
3 reasons why Nicki Minaj: The Empire is...
Nicki Minaj is as business-savvy as she is musically talented and she’s proved that by launching her own game. Designed by Glu, purveyors of other fine celebrity games like cult favorite Kim Kardashian: Hollywood, Nicki Minaj: The Empire launched... | Read more »
Clash of Clans is getting its own animat...
Riding on its unending wave of fame and success, Clash of Clans is getting an animated web series based on its Clash-A-Rama animated shorts.As opposed to the current shorts' 60 second run time, the new and improved Clash-A-Rama will be comprised of... | Read more »
Leaks hint at Pokémon GO and Starbucks C...
Leaked images from a hub for Starbucks employees suggests that a big Pokémon GO event with the coffee giant could begin this very week. The images appeared on Reddit and hint at some exciting new things to come for Niantic's smash hit game. | Read more »
Silent Depth Submarine Simulation (Game...
Silent Depth Submarine Simulation 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: | Read more »
Enneas Saga lets you lead your own demon...
Defend the land of Enneas Continent from the forces of evil in the new fantasy MMORPG from Lyto Mobi: Enneas Saga. Can’t wait? No problem. It’s available to download now on Android devices. | Read more »
Great zombie games in the spirit of Dead...
Dead Rising 4 arrives tomorrow, giving enthusiasts a fresh chance to take selfies with zombies and get up to other ridiculous end-of-the-world shenanigans. To really get into the spirit of things, we've gone and gathered the best zombie games that... | Read more »
Amateur Surgeon 4 Guide: Advanced tips a...
Amateur Surgeon 4 is still tackling the competition at the top of the App Store charts, so if you haven't tried it out yet, you should probably do that right away. If you've been at it for a while, though, perhaps you're ready to start expanding... | Read more »
Amateur Surgeon 4 Guide: Become the worl...
It's time to wield your trusty pizza cutter again, as Amateur Surgeon has returned with a whole fresh set of challenges (and some old, familiar ones, too). Starting anew isn't easy, especially when all you have at your disposal is a lighter, the... | Read more »
Le Parker: Sous Chef Extraordinaire (Ga...
Le Parker: Sous Chef Extraordinaire 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

Back in stock: Apple refurbished Mac minis fr...
Apple has Certified Refurbished Mac minis available starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: - 1.4GHz Mac mini: $419 $80 off MSRP - 2.6GHz Mac... Read more
Twenty-Five Years Of Apple Laptops – A person...
Among many other things, the often tumultuous 16th year of the new century marked the 25th anniversary of Apple laptop computers, not counting the optimistically named 16-pound Mac Portable of 1989.... Read more
Landlordy iOS App Adds Support For Appliances...
Riga, Latvia based E-protect SIA is releasing major update (version 1.8) to its Landlordy app for managing rental business financials on the go. Landlordy is iPhone and iPad app designed for self-... Read more
Holiday sale, Apple iMacs for up to $200 off...
B&H Photo has 21″ and 27″ Apple iMacs on sale for up to $200 off MSRP including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2099 $200 off MSRP - 27″ 3.2GHz/1TB Fusion iMac 5K: $... Read more
Holiday sale: Mac minis for $50 to $100 off M...
B&H Photo has Mac minis on sale for up to $100 off MSRP free shipping plus NY sales tax only: - 1.4GHz Mac mini: $449 $50 off MSRP - 2.6GHz Mac mini: $629 $70 off MSRP - 2.8GHz Mac mini: $899 $... Read more
Mac Pros on sale for up to $300 off MSRP, ref...
B&H Photo has Mac Pros on sale for up to $300 off MSRP. Shipping is free, and B&H charges sales tax in NY only: - 3.7GHz 4-core Mac Pro: $2799, $200 off MSRP - 3.5GHz 6-core Mac Pro: $3699, $... Read more
12-inch WiFi Apple iPad Pros on sale for up t...
B&H Photo has 12″ WiFi Apple iPad Pros on sale for up to $50 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 12″ Space Gray 32GB WiFi iPad Pro: $749 $50 off MSRP... Read more
9-inch Apple WiFi iPad Pros on sale for $20-$...
B&H Photo has 9.7″ Apple WiFi iPad Pros on sale for $20-$50 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 9″ Space Gray 256GB WiFi iPad Pro: $779.95 $20 off MSRP... Read more
Apple refurbished 2015 15-inch MacBook Pros a...
Apple has Certified Refurbished 2015 15″ Retina MacBook Pros available starting at $1699. An Apple one-year warranty is included with each model, and shipping is free: - 15″ 2.2GHz Retina MacBook Pro... Read more
Back in stock! 13-inch 2.7GHz Retina MacBook...
Apple has Apple Certified Refurbished 2015 13″ 2.7GHz/128GB Retina MacBook Pros (MF839LL/A) available again for $1099 including free shipping. That’s $200 off MSRP, and it’s the lowest price... Read more

Jobs Board

*Apple* Retail - Multiple Positions- Philade...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions- San Ant...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Products Tester Needed - Apple (Unit...
…we therefore look forward to put out products to quality test for durability. Apple leads the digital music revolution with its iPods and iTunes online store, Read more
SW Engineer *Apple* TV Frameworks - Apple I...
The Apple TV team is looking for a software...create features that reflect the look and feel of Apple TV. Description: Were looking for someone who is Read more
Hardware Design Validation Engineer - *Apple...
The Apple Watch team is looking for a Hardware Design Validation Engineer. This person will be part of the Apple Watch hardware team with responsibilities for Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.