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.

 
AAPL
$94.72
Apple Inc.
+0.78
MSFT
$44.83
Microsoft Corpora
-0.01
GOOG
$594.74
Google Inc.
+5.27

MacTech Search:
Community Search:

Software Updates via MacUpdate

Airmail 1.4 - Powerful, minimal email cl...
Airmail is a powerful, minimal mail client.It was designed to retain the same experience with a single or multiple accounts and provide a quick, modern and easy-to-use user experience. Airmail... Read more
Macs Fan Control 1.1.12 - Monitor and co...
Macs Fan Control allows you to monitor and control almost any aspect of your computer's fans, with support for controlling fan speed, temperature sensors pane, menu-bar icon, and autostart with... Read more
A Better Finder Rename 9.37 - File, phot...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more
MacBook Air EFI Firmware Update 2.9 - Fo...
MacBook Air EFI Firmware Update is recommended for MacBook Air (Mid 2011) models. This update addresses an issue where systems may take longer to wake from sleep than expected and fixes a rare issue... Read more
FileZilla 3.9.0.1 - Fast and reliable FT...
FileZilla (ported from Windows) is a fast and reliable FTP client and server with lots of useful features and an intuitive interface.Version 3.9.0.1: MSW: Fix installation issue with locked DLLs... Read more
OS X Yosemite 10.10 DP4 - Developer Prev...
Note: This is a Developer Preview. You must be a registered Apple Mac Developer to download this update. OS X Yosemite is Apple's newest operating system for Mac. An elegant design that feels... Read more
FinderPop 2.5.6 - Classic Mac utility, n...
FinderPop is a Universal preference pane that extends OS X's contextual menus using a FinderPop Items folder much as the Apple Menu Items folder used to do for the Apple menu. It has other features... Read more
SpiderOak 5.1.7 - Secure cloud backup, s...
SpiderOak is a multi-platform secure online backup, storage, access, and sharing solution engineered for the consumer and small businesses. You must first sign up to use SpiderOak. Running natively... Read more
Espionage 3.6 - Simple, state of the art...
Espionage offers state-of-the-art encryption and plausible deniability for your confidential data. Sometimes, encrypting your data isn't enough to protect it. That's why Espionage 3 goes beyond data... Read more
calibre 1.45.0 - Complete e-library mana...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital... Read more

Latest Forum Discussions

See All

Celebrate Summer With a Cat in the Hat L...
Celebrate Summer With a Cat in the Hat Learning Library Sale Posted by Ellis Spice on July 22nd, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
MyTaskList Review
MyTaskList Review By Jennifer Allen on July 22nd, 2014 Our Rating: :: EFFECTIVE IF PLAINUniversal App - Designed for iPhone and iPad It’s not the most stylish of task management apps, but MyTaskList has all the features you could... | Read more »
FlyCraft Herbie: Crazy Machines Review
FlyCraft Herbie: Crazy Machines Review By Jennifer Allen on July 22nd, 2014 Our Rating: :: TRICKY FLYINGUniversal App - Designed for iPhone and iPad A tough game of careful thrusting and navigation, FlyCraft Herbie: Crazy Machines... | Read more »
MTN Review
MTN Review By Jessica Fisher on July 22nd, 2014 Our Rating: :: ADORABLE, SERENE, AND AMUSINGUniversal App - Designed for iPhone and iPad MTN is an adorable, talking pet mountain that is less game and more zen garden.   | Read more »
Fly High with Ninja UP! Now Available o...
Fly High with Ninja UP! Now Available on the App Store Posted by Jessica Fisher on July 22nd, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Bio Inc. Review
Bio Inc. Review By Nadia Oxford on July 22nd, 2014 Our Rating: :: SICKENING - IN A COMPELLING WAYUniversal App - Designed for iPhone and iPad Bio Inc is about orchestrating the medical destruction of a single person. If that doesn’... | Read more »
HELMUT Review
HELMUT Review By Andrew Fisher on July 21st, 2014 Our Rating: :: TRUNDLE SIMULATOR 2014Universal App - Designed for iPhone and iPad HELMUT is a fun, fleeting time-sink that offers a momentary distraction and nothing else.   | Read more »
Walkr Review
Walkr Review By Jennifer Allen on July 21st, 2014 Our Rating: :: ORIGINAL WALKINGiPhone App - Designed for the iPhone, compatible with the iPad Walking is a bit more exciting thanks to this planet building/discovering sim reliant... | Read more »
Zombie Commando Review
Zombie Commando Review By Jennifer Allen on July 21st, 2014 Our Rating: :: MINDLESS SLAUGHTERUniversal App - Designed for iPhone and iPad Briefly fun but ultimately forgettable, Zombie Commando will scratch an itch then be... | Read more »
Swords & Poker Adventures Review
Swords & Poker Adventures Review By Jennifer Allen on July 21st, 2014 Our Rating: :: SOULLESS POKER PLAYUniversal App - Designed for iPhone and iPad Swords & Poker Adventures is a mishmash of Poker and RPGing, but it lacks... | Read more »

Price Scanner via MacPrices.net

WaterField Designs Unveils Cycling Ride Pouch...
High end computer case and bag maker WaterField Designs of San Francisco now enters the cycling market with the introduction of the Cycling Ride Pouch – an upscale toolkit with a scratch-free iPhone... Read more
Kingston Digital Ships Large Capacity Near 1T...
Kingston Digital, Inc., the Flash memory affiliate of Kingston Technology Company, Inc.,has announced its latest addition to the SSDNow V300 series, the V310. The Kingston SSDNow V310 solid-state... Read more
15-inch 2.0GHz MacBook Pro Retina on sale for...
B&H Photo has the 15″ 2.0GHz Retina MacBook Pro on sale for $1829 including free shipping plus NY sales tax only. Their price is $170 off MSRP. B&H will also include free copies of Parallels... Read more
Apple restocks refurbished Mac minis for up t...
The Apple Store has restocked Apple Certified Refurbished Mac minis for up to $150 off the cost of new models. Apple’s one-year warranty is included with each mini, and shipping is free: - 2.5GHz Mac... Read more
Twelve South HiRise For MacBook – Height-Adju...
If you use your MacBook as a workhorse desktop substitute, as many of us do, a laptop stand combined with an external keyboard and pointing device are pretty much obligatory if you want to avoid... Read more
Why The Mac Was Not Included In The Apple/IBM...
TUAW’s Yoni Heisler cites Fredrick Paul of Network World whoi blogged last week that the Mac’s conspicuous absence from Apple and IBM’s landmark partnership agreement represents a huge squandered... Read more
Save $100 on 13-inch Retina MacBook Pros, plu...
Adorama has 13″ Retina MacBook Pros on sale for $100 off MSRP. Shipping is free, and Adorama charges sales tax in NY & NJ only: - 13″ 2.4GHz/128GB MacBook Pro with Retina Display: $1199 - 13″ 2.... Read more
Blurr it 2.3 for iOS – Quickly Blurs Selected...
Hyderabad, India based TouchLabs has announced a new update of Blurr it 2.3, their photography app for iOS users. Blurr it allows you to blur part of the image to hide potentially sensitive or... Read more
MacBook Airs on sale for $100 off MSRP, start...
Best Buy has the new 2014 MacBook Airs on sale for up to $100 off MSRP on their online store. Choose free home shipping or free local store pickup (if available). Prices valid for online orders only... Read more
Amazon Announces Kindle Unlimited: Unlimited...
Amazon.com has introduced Kindle Unlimited — a new subscription service which allows customers to freely read as much as they want from over 600,000 Kindle books, and listen as much as they want to... Read more

Jobs Board

Sr Software Lead Engineer, *Apple* Online S...
Sr Software Lead Engineer, Apple Online Store Publishing Systems Keywords: Company: Apple Job Code: E3PCAK8MgYYkw Location (City or ZIP): Santa Clara Status: Full Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Sr *Apple* Engineer - IT - Requisition #: -...
For more information about TIAA-CREF, visit our website . The Apple Engineer will provide engineering and third-level incident support for 300- 500 MacOS desktop/laptop Read more
*Apple* Systems Administrator - DISH (United...
…satellite service provider, and Dish is currently looking for an experienced Apple /Mac Systems Administrator. Apple systems administrator will be responsible for Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.