TweetFollow Us on Twitter

INITs, Patches
Volume Number:5
Issue Number:6
Column Tag:Forth Forum

Related Info: Resource Manager TrapWords

INITs and Patches

By Jörg Langowski, MacTutor Editorial Staff

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

“INITs and trap patches”

This month’s program started off as an attempt to write a ‘logging’ utility, that is, a routine that will record when applications are launched and closed. Simple, I thought. Just patch the _Launch and _ExittoShell traps and install some code that writes a line to a file giving the time, date and name of the application each time these traps are called. However, I soon realized that it’s not as simple as that. Under Finder, yes, that strategy works; but imagine my surprise when I found that _Launch is never called when an application is started under Multifinder! This ‘feature’ seems not to be documented in the technical notes that I have, nor in the Multifinder documentation.

If you record trap calls with TMON, you’ll find the following sequence for launching an application under Finder:

 _Launch
 _LoadSeg 
 _LoadSeg
 ... (until all necessary segments are loaded)

and for exiting, _ExittoShell is called. Multifinder seems to use the same sequence of calls, except for the first call to _Launch, which is left out.

Therefore, if we want to build a routine that logs application launches, we have to find another indicator. One trap call is always made when an application is started: _GetResource is called for CODE ID=0. If we patch _GetResource such that this particular call is intercepted, we have a ‘hook’ that allows us to install any routine to be called at application startup.

Patching traps under Multifinder

Traps cannot be easily patched in a permanent way under Multifinder. Since different application might need different trap patches, Multifinder intercepts (I believe) _SetTrapAddress and switches the trap patches when control is transferred from one program to another. So, when you write a short application that patches a trap, that patch will only be valid in the context of that application - and disappear when the application quits again. Not very useful for a routine that logs application launches, which will have to work independently of any particular context. So we’ll have to install the patch before Multifinder is started, and this is best done with an INIT.

This month’s example will show you how to write an INIT under Mach2 that installs permanent patches to _GetResource and _ExittoShell. For the moment, all these patches do is beep once when the application starts and when it quits. These patches would then have to be extended to write some text to a file that gives the name and time of the application.

I’ll also give an example of a small application that can be used to run an INIT from a file in the same folder as the application. It uses the same mechanism as the system itself to call the INIT. This program is based on an idea of Eric Carrasco from the Calvacom bulletin board in Paris, who wrote a similar program in Pascal.

The INIT

The mechanism by which an INIT resource is called has been outlined already by Bob Denny in V1#9. In case you’re missing that issue, I’ll quickly repeat it here: First, the INIT resource is loaded into the system heap. Then, _DetachResource is called which tells the resource manager to forget this resource. Finally, the system jumps to the first location of the INIT resource via a JSR. When the INIT later returns via RTS, the first two words in its code are overwritten by NOP instructions. The reason for this procedure, which might seem a little strange, is that an INIT code might consist of a JMP to some installation code at the end, and have the actual memory-resident part at its beginning. That way, when the JMP at the beginning is overwritten by NOPs, any code that jumps to the start of the INIT will now execute its main part. The initialization part at the end can be given back to the memory manager, once the INIT is installed.

Listing 1 shows the INIT code in Mach2. The kernel-independent code is produced in the usual way, using the external definition words which make sure the JMP at the first location if the INIT points to the right piece of code, and which set up the local Forth stack.

The INIT (word INITrun) first creates a handle to its own memory block by calling _RecoverHandle, then locks this handle. A temporary area for the Quickdraw globals is then created in the local variable space. Remember that local variables in Mach2 are allocated from top to bottom in memory, so that the sequence

newA5 myGlobals [ 202 lallot ]

with A5 later pointing to the address of newA5 will have the QD globals allocated correctly below A5. If your INIT needs to use any of them, simply reference them starting at myGlobals.

Our INIT code sets up A5 and the low memory global CurrentA5, then calls the usual manager initialization traps necessary for setting up a dialog box. After these calls, the environment is ready for calling the main Forth code of the INIT, myINIT in our case. From myINIT, all toolbox traps may be used since A5 points to valid QD global space and the managers have been initialized (oh not the menu manager, of course, but you probably wouldn’t want to use menus from an INIT. I doubt whether it would be possible, anyway. Try it out).

For an INIT that is supposed to stay in the system heap ‘as is’, you don’t need to take any special action in the code to free its memory space. However, when - as in our case - the INIT copies part of itself to a non-relocatable block in the system heap and is not needed anymore, we want to purge the memory space after action. This is done by calling _DisposHandle after myINIT has returned.

gINIT is the glue code that calls the standard ‘INIT interface’ INITrun. Here, the registers are saved, stacks are set up, and CurrentA5 is restored after INITrun has returned.

The main INIT code, myINIT, first moves the patch code into a non-relocatable block in the system heap. It then patches _GetResource, using _SetTrapAddress, and moves a vector to the trap’s old address into the appropriate location inside the patch. The user is notified of the patch by an alert. The _GetResource patch itself (GetResPatch) checks whether this trap has been called with resource type CODE, ID=0. In that case, it beeps once. Instead of the beep, one could insert some code that writes a line to a file which has been opened in the installation part of the INIT. Something left as an exercise

There is also a patch to _ExittoShell, ExitPatch, which is supposed to beep when an application quits. Now look at the code where the INIT installs that patch. We do a _GetTrapAddress, right, but then the ugly part starts. If _ExittoShell is patched by _SetTrapAddress at system INIT time, the patch gets installed correctly, and you hear the beep when the Finder quits and calls the Multifinder, but then, silence. The patch has disappeared. Multifinder patches _ExittoShell as well and probably doesn’t conserve previous patches. I don’t know whether this is a bug or a feature (such as not calling _Launch when starting an application); but it makes life a great deal more difficult. Apple, can you hear me?

Here’s the workaround that I thought up, which works under System 6.0.2, and is not guaranteed to work under a new release (no, don’t leave the room yet, PLEASE!). When Multifinder patches _ExittoShell, it installs a JMP instruction to its patch code in RAM. Our INIT code tests whether the pointer returned by _GetTrapAddress points to a JMP <absolute> instruction. In that case, it patches the next two words with a pointer to our patch code and saves the old JMP address in the patch code. If the first instruction is not a JMP <absolute>, we assume we’re running under Finder and use _SetTrapAddress to patch the trap. Ugly, isn’t it. The worst part is that if you run under Multifinder your patch will be installed and then removed again; then you have to run the INIT again under Multifinder to install the _ExittoShell patch permanently. But I couldn’t find an easier way, please tell me if you have one.

How can you run an INIT at all when Multifinder runs already? This is where the short runINIT application comes in (Listing 2). This program will simulate the way the system calls an INIT resource. It will locate the file ‘theINIT’ which must be in the same folder, get the INIT ID=12 resource from that file and execute it the same way the system boot code would do it. So for installing the _ExittoShell patch under Multifinder, you simply double-click runINIT in the system folder, or make it one of your startup applications.

INIT incompatibilities

Our INIT is also a practical case where we can document that frequent disease of Mac system folders, INIT incompatibility. This INIT calls all the toolbox managers necessary to set up an alert, and then actually displays one. That means, _WaitNextEvent will be called from the alert. Other INITs might patch _WaitNextEvent, _GetNextEvent or _SystemTask to take some action when the system is fully booted up. That way, for instance, the ‘Remember’ INIT seems to call its associated desk accessory when some important dates are coming up. The problem is, when Remember is executed before an INIT that displays a dialog, the patch will open the desk accessory, which produces disaster in form of a bomb box.

I guess this incompatibility will always occur when you have one INIT which patches _SystemTask or similar routines to execute some other application or DA later on. If another INIT happens to call the patched trap and the system is not ready yet for whatever the first INIT wanted to be executed, a crash will probably follow. Make sure that this INIT is executed before any INITs that patch _WaitNextEvent, _GetNextEvent or _SystemTask.

Mach2 news

Finally I want to advertise the GEnie Mach2 and FIG round tables again. There is simply more interesting stuff in the software libraries than I could ever discuss here; the Mach2 system has been extended by hundreds of useful words already (by the way, v2.15 is on its way), and you find more in the FIG Forth libraries. Especially with the ANSI Forth standard coming up, a lot of the discussion on that new standard - and its implications on Mach2 - takes place on GEnie. For those of you who can’t access GEnie, but have access to Bitnet directly or via a gateway, I’ll try to get a compilation of the most important new words to you if you send me electronic mail:

LANGOWSKI@FREMBL51.BITNET

Happy threading.

Listing 1: Trap patch INIT
\ INIT example which patches _GetResource 
\ with a call to _Sysbeep if type=CODE id=0
\ Also patches _ExitToShell, using an absolutely
\ AWFUL hack, but a _SetTrapAddress patch
\ seems to be removed under Multifinder
\ J. Langowski / MacTutor April 1989
only forth also mac also assembler
( *** compiler support words for external definitions *** )
: :xdef 
 create -4 allot
 $4EFA w, ( JMP )
 0 w,  ( entry point to be filled later )
 0 ,   ( length of routine to be filled later )
 here 6 - 76543
;

: ;xdef { branch marker entry | -- }
 marker 76543 <> abort” xdef mismatch”
 entry branch - branch w!
 here branch - 2+ branch 2+ !
; 
 
: xlen 4 + @ ; ( get length word of external definition )

\ **** ext procedure glue macros

CODE ext.prelude
 LINK A6,#-700   ( 700 bytes of local Forth stack )
 MOVEM.L A0-A5/D0-D7,-(A7)( save registers )
 MOVE.L A6,A3    ( setup local loop return stack )
 SUBA.L #500,A3  ( in the low 200 local stack bytes )
 RTS    \ just to indicate the MACHro stops here 
END-CODE MACH

CODE ext.epilogue
 MOVEM.L (A7)+,A0-A5/D0-D7( restore registers )
 UNLK A6
 RTS
END-CODE MACH

.trap _newPtr,SYS$A51E

-4 CONSTANT thePort
$904    CONSTANT CurrentA5
$A9A0 CONSTANT tGetRes  \ GetResource
$A9F4   CONSTANT tExit    \ ExitToShell

\ |--------------------------------|
\ | INIT resource code starts here |
\ |--------------------------------|

:xdef beeperINIT

header PatchStart
header oldGetRes
 DC.L 0
header oldExit
 DC.L 0

: GetResPatch
 ext.prelude
 CLR.L  D0
 MOVE.W 8(A6),D0
 MOVE.L 10(A6),D1
 MOVE.L D0,-(A6)
 MOVE.L D1,-(A6)

\ main FORTH code starts here
\ this can be used to log any launch
\ (i.e. GetResource CODE 0 ) to a log file
\ which has to be created/opened by the INIT code

 ascii CODE = swap 0= and IF
 \ (call) debugger
 1 (call) sysbeep
 THEN
\ end of main code

 ext.epilogue
 LEA    oldGetRes,A0
 MOVE.L (A0),A0
 JMP    (A0) 
;

: ExitPatch
 ext.prelude

\ main FORTH code starts here
\ this can eventually be used to write a line to 
\ the same log file as before
\(call) debugger
 1 (call) sysbeep
\ end of main code

 ext.epilogue
 LEA    oldExit,A0
 MOVE.L (A0),A0
 JMP    (A0) 
;

header PatchEnd

: movePatch { | length -- patch }
 [‘] patchEnd [‘] PatchStart -   -> length
 length
 MOVE.L (A6)+,D0
 _newPtr,sys
 MOVE.L A0,-(A6)
 dup IF ( we have space in system heap )
 [‘] PatchStart over length swap 
 (call) blockMove drop
 THEN
;
 
: myINIT { | patch pExit -- }
 movePatch -> patch
 patch IF
 \ patch _GetResource
 tGetRes (call) GetTrapAddress
 patch !\  old GetResource
 [‘] GetResPatch [‘] PatchStart -
 patch + tGetRes (call) SetTrapAddress
 “ GetResource patch has been installed.” 
 0 0 0 (call) ParamText
 1000 0 (call) NoteAlert drop

 \ patch _ExitToShell, using hack
 tExit (call) GetTrapAddress -> pExit
 pExit w@ $4EF9 = 
 IF \ is it a JMP <absolute> 
 \ ? we’re probably in Multifinder...
 pExit 2+ @
 patch 4+ ! \  old ExitToShell
 [‘] ExitPatch [‘] PatchStart -
 patch + pExit 2+ ! 
 \ patch directly into Juggler’s innards. BOO!
 “ ExitToShell patch in Multifinder.” 
 0 0 0 (call) ParamText
 1000 0 (call) NoteAlert drop
 ELSE
 pExit patch 4+ !
 [‘] ExitPatch [‘] PatchStart -
 patch + tExit (call) SetTrapAddress
 “ ExitToShell patch in Finder.” 
 0 0 0 (call) ParamText
 1000 0 (call) NoteAlert drop
 THEN
 ELSE
 “ Can’t get memory for patches.”
  0 0 0 (call) ParamText
 1000 0 (call) NoteAlert drop
 THEN
;

: INITrun { | newA5 myGlobals [ 202 lallot ] theHandle -- } 
\(call) debugger 
 [‘] beeperINIT (call) recoverHandle -> theHandle
 theHandle (call) Hlock drop
 ^ newA5
 MOVE.L (A6)+,A5 \ create area for QD globals
 MOVE.L A5,CurrentA5 \ A5 points to it
 ^ newA5 thePort + (call) InitGraf
 (call) InitFonts
 (call) InitWindows
 (call) TEInit
 0 (call) InitDialogs
 (call) InitCursor

 myINIT \ call main INIT routine

 theHandle (call) HUnLock drop
 theHandle (call) DisposHandle drop
;

: gINIT
 ext.prelude INITrun ext.epilogue
 MOVE.L A5,CurrentA5 
;

‘ gINIT ;xdef

( *** creating the INIT file *** )
: $create-res call CreateResFile call ResError L_ext ;

: $open-res { addr | refNum -- result }
 addr call openresfile -> refNum
 call ResError L_ext
 dup not IF drop refNum THEN 
;

: $close-res call CloseResFile call ResError L_ext ;

: make-init { | refNum -- }
 “ theINIT” dup $create-res drop
 $open-res dup -> refNum call UseResFile 
 ascii INIT 12 call GetResource 
 ?dup IF call RmveResource THEN
 [‘] beeperINIT dup xlen
 call PtrToHand drop ( result code )
 ascii INIT 12 call GetResource 
 ?dup IF call RmveResource THEN
 ascii INIT 12 “ Beeper” call AddResource
 refNum $close-res drop ( result code )
;
Listing 2: INIT runner application
\ INIT 12 starter
\ J. Langowski / MacTutor April 1989
\ Thanks to Eric Carrasco (Calvacom EC10) to this idea
\ which he implemented in Pascal
: $open-res { addr | refNum -- result }
 addr call openresfile -> refNum
 call ResError L_ext
 dup not IF drop refNum THEN 
;

: $close-res call CloseResFile call ResError L_ext ;

$4E714E71 CONSTANT nopnop

: runINIT { | refNum hINIT -- }
 “ theInit” $open-res -> refNum
 refNum 0 > IF
 ascii INIT 12 call GetResource -> hINIT
 hINIT IF
 hINIT call HomeResFile
 refNum = IF
 hINIT call DetachResource
 hINIT @ execute \ run the INIT
 nopnop hINIT @ !  
 \ fill first 2 words with NOPs
 ELSE
 “ INIT not from my file” 0 0 0 call ParamText
 1000 0 call NoteAlert drop
 THEN
 ELSE
 “ Can’t find INIT 12 resource” 
 0 0 0 call ParamText
 1000 0 call NoteAlert drop
 THEN
 ELSE
 “ Can’t open file ‘theINIT’” 0 0 0 call ParamText
 1000 0 call NoteAlert drop
 THEN
 bye
;
 

Community Search:
MacTech Search:

Software Updates via MacUpdate

GraphicConverter 10.5 - $39.95
GraphicConverter is an all-purpose image-editing program that can import 200 different graphic-based formats, edit the image, and export it to any of 80 available file formats. The high-end editing... Read more
Dropbox 35.4.20 - Cloud backup and synch...
Dropbox is an application that creates a special Finder folder that automatically syncs online and between your computers. It allows you to both backup files and keep them up-to-date between systems... Read more
XMind 8 Update 4 - Popular mind mapping...
XMind is the most popular mind mapping tool. Millions of people use XMind to clarify thinking, manage complex information, run brainstorming and get work organized. It couldn't be easier to get... Read more
Safari Technology Preview 11.1 - 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
Chromium 61.0.3163.91 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. Version 61.0.3163.91: Release notes were unavailable... Read more
RapidWeaver 7.5.1 - Create template-base...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
Google Chrome 61.0.3163.91 - Modern and...
Google Chrome is a Web browser by Google, created to be a modern platform for Web pages and applications. It utilizes very fast loading of Web pages and has a V8 engine, which is a custom built... Read more
Quicken 4.6.3 - Complete personal financ...
Quicken makes managing your money easier than ever. Whether paying bills, upgrading from Windows, enjoying more reliable downloads, or getting expert product help, Quicken's new and improved features... Read more
TechTool Pro 9.5.3 - Hard drive and syst...
TechTool Pro has long been one of the foremost utilities for keeping your Mac running smoothly and efficiently. With the release of version 9, it has become more proficient than ever. TechTool... Read more
PDFKey Pro 4.3.9 - Edit and print passwo...
PDFKey Pro can unlock PDF documents protected for printing and copying when you've forgotten your password. It can now also protect your PDF files with a password to prevent unauthorized access and/... Read more

Stormbound: Kingdom Wars guide - how to...
Stormbound: Kingdom Wars is an excellent new RTS turned card battler out now on iOS and Android. Lovers of strategy will get a lot of enjoyment out of Stormbound's chess-like mechanics, and it's cardbased units are perfect for anyone who loves the... | Read more »
The best AR apps and games on iOS right...
iOS 11 has officially launched, and with it comes Apple's ARKit, a helpful framework that makes it easier than ever for developers to create mobile AR experiences. To celebrate the occassion, we're featuring some of the best AR apps and games on... | Read more »
Phoenix Wright: Ace Attorney - Spirit of...
Phoenix Wright: Ace Attorney - Spirit of Justice 1.00.00 Device: iOS Universal Category: Games Price: $.99, Version: 1.00.00 (iTunes) Description: ************************************************※IMPORTANT※・Please read the “When... | Read more »
Kpressor (Utilities)
Kpressor 1.0.0 Device: iOS Universal Category: Utilities Price: $4.99, Version: 1.0.0 (iTunes) Description: The ultimate ZIP compression application for iPhone and iPad. - Full integration of iOS 11 with support for multitasking.-... | Read more »
Find out how you can save £35 and win a...
Nothing raises excitement like a good competition, and we’re thrilled to announce our latest contest. We’ll be sending one lucky reader and a friend to the Summoners War World Arena Championship at Le Comedia in Paris on October 7th. It’s the... | Read more »
Another Lost Phone: Laura's Story...
Another Lost Phone: Laura's Story 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Another Lost Phone is a game about exploring the social life of a young woman whose phone you have just... | Read more »
The Witness (Games)
The Witness 1.0 Device: iOS Universal Category: Games Price: $9.99, Version: 1.0 (iTunes) Description: You wake up, alone, on a strange island full of puzzles that will challenge and surprise you. You don't remember who you are, and... | Read more »
Egg, Inc. guide - how to build your gold...
Egg, Inc.'s been around for some time now, but don't you believe for one second that this quirky clicker game has gone out of style. The game keeps popping up on Reddit and other community forums thanks to the outlandish gameplay (plus, the... | Read more »
The best deals on the App Store this wee...
Good news, everyone! Your favorite day of the week has arrived at last -- it's discount roundup day! This fine Wednesday evening we're gathering up the hottest deals on the App Store. We've got action platformers, we've got puzzle games, we've got... | Read more »
Morphite (Games)
Morphite 1.08 Device: iOS Universal Category: Games Price: $7.99, Version: 1.08 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

OWC USB-C Travel Dock with 5 Ports Connectivi...
OWC have announced the new OWC USB-C Travel Dock, the latest addition to their line of connectivity solutions. The USB-C Travel Dock lets you connect its integrated USB-C cable to a Mac or PC laptop... Read more
Pelican Products, Inc. Unveils Cases For All...
Pelican Products, Inc. has announced the launch of its full line of cases including Voyager, Adventurer, Protector, Ambassador, Interceptor (for the Apple iPhone 8 and 8 Plus backwards compatible... Read more
$100 off new 2017 13-inch MacBook Airs
B&H Photo has 2017 13″ MacBook Airs on sale today for $100 off MSRP including free shipping. B&H charges NY & NJ sales tax only: – 13″ 1.8GHz/128GB MacBook Air (MQD32LL/A): $899, $100 off... Read more
Apple restocks Certified Refurbished 13-inch...
Apple has Certified Refurbished 2015 13″ MacBook Airs available starting at $719 and 2016 models available starting at $809. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Is iPhone X Really The Future Of The Smartpho...
Should iPhone X even be called a telephone? It does of course support telephony and texting, but its main feature set is oriented to other things. It is also debatable whether it makes any rational... Read more
OtterBox Announces Full Case Lineup for iPhon...
Apple revolutionized the smartphone industry 10 years ago with the original iPhone, and OtterBox has set the standard of protection from the very beginning by protecting every generation of iPhone.... Read more
LifeProof Introduces What’s NEXT Cases for iP...
LifeProof built its reputation on sleek, ultra-protective iPhone cases. From 360-degree coverage to the first screenless waterproof case, the protection pioneer has always pushed the limits.... Read more
Apple Refurbished 2016 15-inch MacBook Pros a...
Apple has Certified Refurbished 2016 15″ Touch Bar MacBook Pros available starting at $1949. An Apple one-year warranty is included with each model, and shipping is free: – 15″ 2.7GHz Touch Bar Space... Read more
Wednesday deal: 15-inch MacBook Pros for up t...
B&H Photo has 2017 15″ MacBook Pros on sale for $150-$200 off MSRP. Shipping is free, and B&H charges sales tax in NY & NJ only: – 15″ 2.8GHz MacBook Pro Space Gray: $2199, $200 off MSRP... Read more
2.6GHz Mac mini on sale for $599, $100 off MS...
B&H Photo has the 2.6GHz Mac mini (MGEN2LL/A) on sale for $599 including free shipping plus NY sales tax only. Their price is $100 off MSRP. Read more

Jobs Board

Development Operations and Site Reliability E...
Development Operations and Site Reliability Engineer, Apple Payment Gateway Job Number: 57572631 Santa Clara Valley, California, United States Posted: Jul. 27, 2017 Read more
Full time *Apple* Hardware Tech needed - ma...
…high level of attention to detail Ethics, integrity and trust Be a geek & Previous Apple experience a must. Previous Apple Retail or other Apple Specialist Read more
Development Operations and Site Reliability E...
Development Operations and Site Reliability Engineer, Apple Payment Gateway Job Number: 57572631 Santa Clara Valley, California, United States Posted: Jul. 27, 2017 Read more
*Apple* Store - Technical Specialist - Apple...
…customers purchase our products, you're the one who helps them get more out of their new Apple technology. Your day in the Apple Store is filled with a range of Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.