TweetFollow Us on Twitter

Universal Headers Gotcha
Volume Number:11
Issue Number:5
Column Tag:Compiler Settings

The Devil’s In The Details

Don’t get surprised by the Universal Headers

By Bill Karsh, billKarsh@aol.com

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

There is a particularly insidious problem in Apple’s Universal Headers. Whether you are affected at all, and how devastating it is, depends upon how you use their headers in your projects. Fortunately, the problem only affects 68K code generation. Here are the details, and what you can do as a work-around until new headers become available.

Which Header Versions?

The problem appears in the headers I got with Think C/C++ version 7, although these headers themselves do not seem to have a version number. The problem persists through the latest headers I got with MetroWerks CodeWarrior 5. These are version 2.0a3. Undoubtedly, you are using an affected version (I think they all are).

Structure Alignment Problem

The problem is a structure alignment conflict. Most compilers today let you apply some options regarding how structures are defined, throughout the whole of a project, or while certain pragmas are in effect. For example, you find a pop-up menu in CodeWarrior’s Processor Preferences panel, that let’s you select options called “68K,” “68K 4-byte,” or “PowerPC.” You can also use pragma statements like these:

#pragma options align=mac68k
#pragma options align=mac68k4byte
#pragma options align=native
#pragma options align=power
#pragma options align=reset

These can be used to override a globally set option. I believe that the last option stays in effect until either the next alignment statement, or the end-of-file is encountered.

In Symantec C++, the Compiler Settings page has a radio button group called “Struct Field Alignment,” that sets alignment options for a project.

Generally, the chosen alignment determines how much padding (extra space) is inserted into structures between fields, and how much padding is appended to the end of structures. Deciding which option you would want is a matter of trading-off between compactness of the data (less space) and higher performance (fields aligned on natural addresses for the field’s data-type). We won’t go into those decisions here. What is immediately essential is understanding two things.

First, these options are available to you (settable in an options page or by pragma statements) independently of whether you are generating PowerPC (ppc) code or 68K code.

Second, structures defined by the Mac OS, that is, defined in Apple’s headers, must have no extra padding in them. When the compiler comes across the definition of any Mac OS structure, like GrafPort, BitMap, or whatever, the current alignment option must be mac68k. If the current setting were anything else, your code, and the system software, would disagree on the offsets to various fields in a GrafPort, for example. That’s a disaster.

Inside Mac Headers

If you look inside virtually any Apple header, you will see one of the following examples near the top of the file:

#if defined(powerc) || defined (__powerc)
#pragma options align=mac68k
#endif

or

#if GENERATINGPOWERPC
#pragma options align=mac68k
#endif

Near the bottom you will see one of:

#if defined(powerc) || defined (__powerc)
#pragma options align=reset
#endif

or

#if GENERATINGPOWERPC
#pragma options align=reset
#endif

The intent here is to force the alignment type to mac68k while any Mac OS structures are defined. Then, align=reset puts the alignment back to whatever was in effect before. Can you see the problem? The pragma statements are made conditional upon what type of code is being generated, ppc or 68K. If you are generating ppc code only, there is no problem. If you are generating 68K code, the pragmas are not executed. You’ve got a bad problem in 68K code if, when the headers are compiled, the current alignment option is not mac68k. The pragma statements in the Apple headers were not supposed to be conditional upon anything. I’m guessing here, but it looks like a clear case of macro-mania-a-go-go.

Why Didn’t I See That?

I know, right now you are saying “how can any of my code work at all if this is true? Why didn’t I catch this immediately!?” There are several sneaky ways this problem might have escaped your notice thus far. For one thing, 68K compilers typically ship with mac68k as the default alignment option. If you never changed that, you would have been spared. Another possibility involves precompiled headers.

Your environment was shipped with precompiled headers. That is, many, but not all, of the Apple headers were precompiled at the factory into a giant header called MacHeaders68K (CW) or MacHeaders (Think), or something similar. Such a file is usually included in a global preferences dialog. That would be the Language panel in CW, or the Prefix page in Think’s dialog. There may be separate precompiled headers for C and C++. Again, chances are that you never removed it. Back at the factory, they compiled these precompiled files using the mac68k setting. Therefore, all the structures defined in there are fine. However, not all of the Apple headers are typically included in these things, only the most commonly used. This keeps symbol table sizes down, and speeds compile times.

Any time you find a need to explicitly include an Apple header in your sources, and it’s not among those precompiled at the factory, you are letting yourself in for it. You have to do something to make sure that when the compiler reads that included header, the alignment is mac68k. You have to take these steps yourself because the provision to do this automatically in the headers themselves is incorrectly coded.

What Do I Do?

If you understand what’s happening, you can choose whatever method you like to adjust for this; whatever works and is convenient. Let’s suppose you need Timer.h, and it’s not currently precompiled. Here are some possibilities:

Re-precompile MacHeaders68K, or whichever variant your project needs. Uncomment Timer.h in the source file that generates the precompiled header. Make sure the project’s global option is “68K” (CW) or “Align to 1 byte Boundary” (Think). Precompile a new MacHeaders, and include it in your working project’s preferences dialog.

Include Timer.h in a source file like this:

#pragma options align=mac68k
#include <Timer.h>
#pragma options align=reset

Repair the Apple header directly. Change this:

#if GENERATINGPOWERPC
#pragma options align=mac68k
#endif

to this:

#pragma options align=mac68k

Make the alignment options unconditional, as they were supposed to be. Do this for the reset lines too!

I know this will save you days of debugging and thousands of dollars of development costs. Could you send me just one dollar as a thank you? Worth a try.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

CleanMyMac 3.9.0 - $39.95
CleanMyMac makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac lets you safely and intelligently scan and clean your entire system, delete large, unused files... Read more
Apple High Sierra 10.13 - The latest OS...
macOS High Sierra introduces new core technologies that improve the most important functions of your Mac. From rearchitecting how it stores your data to improving the efficiency of video streaming to... Read more
OmniGraffle Pro 7.4.3 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
OmniGraffle 7.4.3 - Create diagrams, flo...
OmniGraffle helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use Graffle to... Read more
VueScan 9.5.86 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
ExpanDrive 6.1.0 - Access cloud storage...
ExpanDrive builds cloud storage in every application, acts just like a USB drive plugged into your Mac. With ExpanDrive, you can securely access any remote file server directly from the Finder or... Read more
Yojimbo 4.1 - Data information organizer...
Yojimbo empowers Mac users to manage, effortlessly and securely, the onslaught of information encountered every day at work and at home, even across multiple computers. Yojimbo stores different data... Read more
Airmail 3.5 - Powerful, minimal email cl...
Airmail is an mail client with fast performance and intuitive interaction. Support for iCloud, MS Exchange, Gmail, Google Apps, IMAP, POP3, Yahoo!, AOL, Outlook.com, Live.com. Airmail was designed... Read more
Cocktail 11.0 - General maintenance and...
Cocktail is a general purpose utility for macOS that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Numi 3.17.2 - Menu-bar calculator suppor...
Numi is a calculator that magically combines calculations with text, and allows you to freely share your computations. Numi combines text editor and calculator Support plain English. For example, '5... Read more

The best visual novels on mobile
Narrative games have been around for ages, but only now have they been creeping into the mainstream spotlight. These games tell some of the industry's finest stories, and they break new ground in terms of gameplay and mechanics regularly. Here are... | Read more »
The best new games we played this week -...
It's pretty much been one big release after another. We were privy to a bunch of surprises this week, with a lot of games we'd been waiting for quite some time dropping unexpectedly. We hope you're free this weekend, because there is a lot for... | 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 »

Price Scanner via MacPrices.net

Snag a Certified Refurbished Apple Pencil for...
Apple has Certified Refurbished Apple Pencils available for $85 including free shipping. Their price is $14 off MSRP, and it’s the lowest price available for a Pencil. Read more
12-inch 64GB iPad Pro on sale for $749, save...
Adorama has 12″ 64GB iPad Pros on sale today for $749 including free shipping plus NY & NJ sales tax only. Their price is $50 off MSRP. Read more
Apple Certified Refurbished iPad minis availa...
Apple has Certified Refurbished 128GB iPad minis available today for $339 including free shipping. Apple’s standard one-year warranty is included. Their price is $60 off MSRP. Read more
12-inch 1.2GHz Retina MacBook Pros on sale fo...
B&H Photo has 2017 12″ 1.2GHz Retina MacBooks on sale for $100 off MSRP. Shipping is free, and B&H charges sales tax in NY & NJ only: 12″ 1.2GHz Space Gray MacBook: $1199 $100 off MSRP 12... Read more
Sunday sale: 13-inch 3.1GHz MacBook Pros for...
Amazon has 2017 13″ 3.1GHz MacBook Pros on sale today for up to $150 off MSRP, each including free shipping: – 13″ 3.1GHz/256GB Space Gray MacBook Pro (MPXV2LL/A): $1649.99 $150 off MSRP – 13″ 3.1GHz... Read more
Looking for a 2017 12″ Retina MacBook? Save $...
Apple has Certified Refurbished 2017 12″ Retina MacBooks available for $200-$240 off the cost of new models. Apple will include a standard one-year warranty with each MacBook, and shipping is free.... Read more
Apple Offering Up To $455 Credit Toward iPhon...
iPhone 8 and 8 Plus are now available at the Apple Store, and you can receive up to $375 credit toward a new iPhone purchase when you trade in your eligible smartphone. Photo Courtesy Apple Just... Read more
AnyTrans Offers iOS Users Three Ways For Movi...
iMobie Inc. today announceed AnyTrans v6.0.1, which now can help iOS users move all data to iPhone 8/8 Plus seamlessly. The software is available both on Mac and Windows and fully able to move all... Read more
Snag a 13-inch 2.3GHz MacBook Pro for $100 of...
B&H Photo has 2017 13″ 2.3GHz MacBook Pros in stock today and on sale for $100 off MSRP, each including free shipping plus NY & NJ sales tax only: – 13-inch 2.3GHz/128GB Space Gray MacBook... Read more
Verizon offers new iPhone 8 for $100-$300 off...
Verizon is offering the new iPhone 8 for up to $300 off MSRP with an eligible trade-in: • $300 off: iPhone 6S/6S Plus/7/7 Plus, Google Pixel XL, LG G6, Moto Z2 Force, Samsung Galaxy S7/S7 edge/S8/S8... Read more

Jobs Board

Data Engineer - *Apple* Media Products - Ap...
Job Summary Apple is seeking a highly skilled data engineer to join the Data Engineering team within Apple Media Products. AMP (home to Apple Music, App 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
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* 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
Instructional Designer, *Apple* Product Doc...
Job Summary The Apple Product Documentation team is looking for an instructional designer or a video editor to write user documentation for its professional video Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.