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

Chromium 75.0.3770.142 - 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 75.0.3770.142: Release notes were... Read more
Viber 11.1.0 - Send messages and make fr...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device, so... Read more
Wireshark 3.0.3 - Network protocol analy...
Wireshark is one of the world's foremost network protocol analyzers, and is the standard in many parts of the industry. It is the continuation of a project that started in 1998. Hundreds of... Read more
DEVONthink Pro 3.0beta4 - Knowledge base...
DEVONthink Pro is your essential assistant for today's world, where almost everything is digital. From shopping receipts to important research papers, your life often fills your hard drive in the... Read more
Adobe Creative Cloud 4.9.0.512 - Access...
Adobe Creative Cloud costs $20.99/month for a single app, or $52.99/month for the entire suite. Introducing Adobe Creative Cloud desktop applications, including Adobe Photoshop CC and Illustrator CC... Read more
SketchUp 19.1.174 - Create 3D design con...
SketchUp is an easy-to-learn 3D modeling program that enables you to explore the world in 3D. With just a few simple tools, you can create 3D models of houses, sheds, decks, home additions,... Read more
ClamXav 3.0.12 - Virus checker based on...
ClamXav is a popular virus checker for OS X. Time to take control ClamXAV keeps threats at bay and puts you firmly in charge of your Mac’s security. Scan a specific file or your entire hard drive.... Read more
BetterTouchTool 3.151 - Customize multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom)... Read more
FontExplorer X Pro 6.0.9 - Font manageme...
FontExplorer X Pro is optimized for professional use; it's the solution that gives you the power you need to manage all your fonts. Now you can more easily manage, activate and organize your... Read more
Dropbox 77.4.131 - Cloud backup and sync...
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 keeps them up-to-date between systems... Read more

Latest Forum Discussions

See All

Upcoming visual novel Arranged shines a...
If you’re in the market for a new type of visual novel designed to inform and make you think deeply about its subject matter, then Arranged by Kabuk Games could be exactly what you’re looking for. It’s a wholly unique take on marital traditions in... | Read more »
TEPPEN guide - The three best decks in T...
TEPPEN’s unique take on the collectible card game genre is exciting. It’s just over a week old, but that isn’t stopping lots of folks from speculating about the long-term viability of the game, as well as changes and additions that will happen over... | Read more »
Intergalactic puzzler Silly Memory serve...
Recently released matching puzzler Silly Memory is helping its fans with their intergalactic journeys this month with some very special offers on in-app purchases. In case you missed it, Silly Memory is the debut title of French based indie... | Read more »
TEPPEN guide - Tips and tricks for new p...
TEPPEN is a wild game that nobody asked for, but I’m sure glad it exists. Who would’ve thought that a CCG featuring Capcom characters could be so cool and weird? In case you’re not completely sure what TEPPEN is, make sure to check out our review... | Read more »
Dr. Mario World guide - Other games that...
We now live in a post-Dr. Mario World world, and I gotta say, things don’t feel too different. Nintendo continues to squirt out bad games on phones, causing all but the most stalwart fans of mobile games to question why they even bother... | Read more »
Strategy RPG Brown Dust introduces its b...
Epic turn-based RPG Brown Dust is set to turn 500 days old next week, and to celebrate, Neowiz has just unveiled its biggest and most exciting update yet, offering a host of new rewards, increased gacha rates, and a brand new feature that will... | Read more »
Dr. Mario World is yet another disappoin...
As soon as I booted up Dr. Mario World, I knew I wasn’t going to have fun with it. Nintendo’s record on phones thus far has been pretty spotty, with things trending downward as of late. [Read more] | Read more »
Retro Space Shooter P.3 is now available...
Shoot-em-ups tend to be a dime a dozen on the App Store, but every so often you come across one gem that aims to shake up the genre in a unique way. Developer Devjgame’s P.3 is the latest game seeking to do so this, working as a love letter to the... | Read more »
Void Tyrant guide - Guildins guide
I’ve still been putting a lot of time into Void Tyrant since it officially released last week, and it’s surprising how much stuff there is to uncover in such a simple-looking game. Just toray, I finished spending my Guildins on all available... | Read more »
Tactical RPG Brown Dust celebrates the s...
Neowiz is set to celebrate the summer by launching a 2-month long festival in its smash-hit RPG Brown Dust. The event kicks off today, and it’s divided into 4 parts, each of which will last two weeks. Brown Dust is all about collecting, upgrading,... | Read more »

Price Scanner via MacPrices.net

Verizon is offering a 50% discount on iPhone...
Verizon is offering 50% discounts on Apple iPhone 8 and iPhone 8 Plus models though July 24th, plus save 50% on activation fees. New line required. The fine print: “New device payment & new... Read more
Get a new 21″ iMac for under $1000 today at t...
B&H Photo has new 21″ Apple iMacs on sale for up to $100 off MSRP with models available starting at $999. These are the same iMacs offered by Apple in their retail and online stores. Shipping is... Read more
Clearance 2017 15″ 2.8GHz Touch Bar MacBook P...
Apple has Certified Refurbished 2017 15″ 2.8GHz Space Gray Touch Bar MacBook Pros available for $1809. Apple’s refurbished price is currently the lowest available for a 15″ MacBook Pro. An standard... Read more
Clearance 12″ 1.2GHz MacBook on sale for $899...
Focus Camera has clearance 12″ 1.2GHz Space Gray MacBooks available for $899.99 shipped. That’s $400 off Apple’s original MSRP. Focus charges sales tax for NY & NJ residents only. Read more
Get a new 2019 13″ 2.4GHz 4-Core MacBook Pro...
B&H Photo has new 2019 13″ 2.4GHz MacBook Pros on sale for up to $150 off Apple’s MSRP. Overnight shipping is free to many addresses in the US: – 2019 13″ 2.4GHz/256GB 6-Core MacBook Pro Silver... Read more
AirPods with Wireless Charging Case now on sa...
Amazon has extended their Prime Day savings on Apple AirPods by offering AirPods with the Wireless Charging case for $169.99. That’s $30 off Apple’s MSRP, and it’s the cheapest price available for... Read more
New 2019 15″ MacBook Pros on sale for $200 of...
B&H Photo has the new 2019 15″ 6-Core and 8-Core MacBook Pros on sale for $200 off Apple’s MSRP. Overnight shipping is free to many addresses in the US: – 2019 15″ 2.6GHz 6-Core MacBook Pro Space... Read more
Amazon drops prices, now offers clearance 13″...
Amazon has new dropped prices on clearance 13″ 2.3GHz Dual-Core non-Touch Bar MacBook Pros by $200 off Apple’s original MSRP, with prices now available starting at $1099. Shipping is free. Be sure to... Read more
2018 15″ MacBook Pros now on sale for $500 of...
Amazon has dropped prices on select clearance 2018 15″ 6-Core MacBook Pros to $500 off Apple’s original MSRP. Prices now start at $1899 shipped: – 2018 15″ 2.2GHz Touch Bar MacBook Pro Silver: $1899.... Read more
Price drop! Clearance 12″ 1.2GHz Silver MacBo...
Amazon has dropped their price on the recently-discontinued 12″ 1.2GHz Silver MacBook to $849.99 shipped. That’s $450 off Apple’s original MSRP for this model, and it’s the cheapest price available... Read more

Jobs Board

Best Buy *Apple* Computing Master - Best Bu...
**696259BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Store Associates **Location Number:** 001076-Temecula-Store **Job Description:** The Read more
Business Development Manager, *Apple* Globa...
Business Development Manager, Apple Global Tampa, FL, US Requisition Number:73805 As a Global Apple Business Development Manager at Insight, you proactively Read more
*Apple* Systems Architect/Engineer, Vice Pre...
…its vision to be the world's most trusted financial group. **Summary:** Apple Systems Architect/Engineer with strong knowledge of products and services related to Read more
*Apple* IOS Systems Engineer - Randstad (Uni...
Apple IOS Systems Engineer **job details:** + location:Irvine, CA + salary:$45 - $55 per hour + date posted:Tuesday, July 16, 2019 + job type:Temp to Perm + Read more
Business Development Manager, *Apple* Globa...
Business Development Manager, Apple Global Tampa, FL, US Requisition Number:73805 As a Global Apple Business Development Manager at Insight, you proactively Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.