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I want to decompile a iOS 3.1.3 kernel to better understand it, but i'm not sure where to start, But don't be fooled i'm no green horn when it comes to programming.
The kernel is open source so you can view and compile it. iOS 3.1.3 is in the repo but you will also want to look at 3.0.
From Apple:
As the first major computer company to make Open Source development a key part of its ongoing software strategy, Apple remains committed to the Open Source development model. Major components of Mac OS X, including the UNIX core, are made available under Apple’s Open Source license, allowing developers and students to view source code, learn from it and submit suggestions and modifications.
The XNU kernel in its iOS incarnation is not open source, though xnu in its i386/x86_84 (and , for older versions PPC) is.
XNU is built up internally of several layers, with the bottom two - platform expert and ml_* APIs serving as the "glue" to the underlying hardware. This means that without said pieces you could compile the source (with an ARMv7 cross compiler, like the one in the iPhone SDK), but the kernel wouldn't actually boot.
Another difficulty is in the kernel extensions (XNU-speak for "modules"). These are drivers, without which you can't really do much - again, with the kernel not booting since it can't initialize any of its platform dependencies.
Also, contrary to how it may seem, though the iOS and OS X kernels are very similar, there are some subtle differences (which were visible by #ifdef CONFIG_EMBEDDED and #ifdef ARM until after 1699, when Apple realized they were leaking information of use to jailbreakers, and finally used a preprocessor to strip the iOS specific modifications before making it public.
Decompilation is a different matter. It's possible to disassemble and work back, from the kernel image (once decrypted or dumped) through fairly readable assembly (though not to a full source level). IDA and other specialized tools (e.g. jtool) have these capabilities.
There have been at least two projects to get the open source version to compile and boot for ARM. One by Christina Brooks(?) and another by WinOCM. The latter, which has gained notoriety for knowing XNU in its ARM implementation inside out, has eventually been employed by Apple, thereby reducing the chance of any open source implementation ever seeing the light of day.
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As someone who has never developed an iOS app but hopes to soon and has never had a Mac (to date) the whole XCode and process for developing apps was a little lost on me.
To start: things like which languages are supported in development was one area I wasn't sure of:
I've seen C, C++ and Objective-C referenced as the languages used to write the apps. But I've also seen JavaScript` + HTML + CSS and .NET as options and a host of other compiled languages, with people arguing if you can or can't use them.
Another thing I wondered about was Xcode, does it support all the mentioned languages? Or is an IDE built for a specific language such as Cocoa ? If it is, then how would someone use JavaScript for example to write the app?
I'm sure this is a fairly simple answer to Apple users, but I had some struggle trying to relate from a non-Apple background.
Updated
Thanks for the great answers and insight, hopefully other this post will be helpful to others who don't have an Apple / iOS background
All three language alternatives that you mentioned are available to iOS application developers *.
Objective-C/C++ offers a way of making native apps for iOS, you produce machine code that runs on the devices. You use Xcode to develop in these languages.
You can build apps in JavaScript + HTML + CSS because iOS comes with a browser. Apple offers a mode that gives your apps a completely native look and feel, so they do look like first-class citizens.
You can build your apps in C# as well by using Mono Touch. This is different from .NET, although the language is the same, because your code is compiled into binary ahead of time. Although using Mono Touch eliminates the learning curve associated with the new language, you need to go through a fair bit of learning to adapt your knowledge of .NET to a different platform.
* Except Cocoa, which is not a language, but a collective name for Apple's frameworks for developing under OS X and iOS.
iOS' native language is Objective-C. While it's true you can use C++ to make apps (Cocos for example, is mostly written in C++) it isn't the 'native language'.
As for the other languages you mention, while it's possible to create apps using them they won't be 'native' normally relying upon another IDE/Library, phone gap or adobe air for example. Most of these also support cross platform development.
Where I work we also use HTML5 to create a 'faux native' interface/experience.
If you're new to iOS it's worth while checking out Apple documentation/sample code at:
https://developer.apple.com
There is a wealth of knowledge there that should set you on the right path. It ins't however, something I'd recommend if you don't have any experience with object orientated programming.
Coming from a C++ background myself, I didn't find it too difficult but have been working on iOS for about 3 years (on and off) and am only just starting to really become truly fluent in it's processes and conventions.
Hope this helps, let me know if you want to know anything specific.
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I was checking the portability of a tool using Z3 (2012-12-21 git version, the latest "master" release), and thus tried compiling Z3 on Sparc64. I had to fiddle with src/util/hwf.cpp so that it would treat Sparc64, and not just IA64, as lacking SIMD intrinsics and emmintrin.h. The compilation succeeded.
Unfortunately, the resulting executable crashes on startup with a bus error in prime_generator::prime_generator(). I have no idea why.
Program received signal SIGBUS, Bus error.
0x009b1dac in global constructors keyed to _ZN15prime_generatorC2Ev ()
(gdb) bt
#0 0x009b1dac in global constructors keyed to _ZN15prime_generatorC2Ev ()
This is not very important for me (our machines are x86 or x86-64) but may be relevant for some embedded applications.
I don't think there has been any interest in running Z3 on non-x86 machines, so it's highly likely that you'll find a few problems.
SPARC, in particular, doesn't allow unalighed memory accesses, as x86 does.
From a quick look, I could see several points where the unaligned could come from.
For example, memory::allocate() dealigns the pointer returned by malloc by sizeof(size_t). If that's not 64 bits, then it will crash (because of the svector data).
Then, svector allocation, also reserves 2*sizeof(unsigned) before the data. If 2*sizeof(unsigned) is not a multiple of sizeof(uint64), then you'll get a crash.
And so on. The point is that without more info, it's impossible to help you. You need to compile with -g, and if needed print the assembly code where it's crashing to help pin point the exact location.
Also, don't use the master branch, please. That's very old. Please consider using the unstable branch (it's not that bad as the name may sound :)
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Do they use some algorithm such as the ones used in GDIFF program?
Do they ship the intermediate code to the user instead of iOS binary?
Why is it not possible do do a Delta update while updating iOS on Windows?
A delta update is defined as 'an update that only requires the user to download the code that has changed, not the whole program.'
iOS does, in fact, perform delta updates, and contradictory to Ralph's comment, we know exactly how it works.
Applications
For iOS applications, delta updates are used to minimize the download size of new versions, to save internet traffic. Usually, the things that give a program most of its size are the static images and other media. During a simple update such as a bug fix, usually these static images stay the same, and there is no reason to send them over the network again. The only thing that is sent is the actual Mach-O binary containing the code that is buggy, along with whatever files have been changed.
So, delta updates most likely run by checksumming. When you submit an app update, Apple checks the checksum of all files submitted using some algorithm (most likley SHA1 or MD5) to scan for changes. If the executable has changed, but a certain image or other file has not, the image isn't packed with the update, as users have already downloaded it, and don't need to download it again. While this method may not pertain exactly to the definition of a delta update, as it includes executables along with other types of files, it has very similar concepts.
OTA Updates
Apple uses delta updates in over-the-air updates for iOS as well. This is visible on any jailbroken iOS device. Updates are downloaded to /var/MobileSofwareUpdate/softwareupdate.xxxx, where xxxx presumbably is the build/release number. Each software update contains an image of the root filesystem, but not the entire version of iOS is included. Only the files that have changed from the version the user is currently on need to be replaced, and so only those files are included in the update package. The method for finding these changes is likley to be the same as with iOS apps, where checksumming finds changes in the files.
Algorithm
Basically, to answer your question, Apple's algorithm doesn't send the differences between two individual files (similar to what you see in a git commit), but sends the entire updated file. Their 'algorithm' just looks for any change at all between the last version, and doesn't look for the actual change itself. This is proven by the fact that in OTA update packages, the complete files are available, and not just a log of the changes.
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NB: This question has been extensively edited to make it more relevant, for completeness the original question maintained at the end.
What version(s) of iOS should my App support?
When building a new iOS app what a strategies should one use to determine what versions of the operating system to support? What practical considerations are there in supporting legacy OS version. Are there any reliable statistics to support the business case of dropping legacy support?
Original Question
If I build a new iOS application, should I support iOS versions prior to 5.0, or is that not necessary anymore? Is there any reliable and up to date data on iOS 5.0 adoption rates?
iOS Support Matrix v3.0.1
This version is updated and includes iOS 7.1 and new iPads.
Link: http://www.iossupportmatrix.com
According to this article: http://thenextweb.com/apple/2012/03/06/why-do-developers-prefer-ios-over-android-try-75-adoption-of-ios-5-while-ics-is-stuck-at-1/
the adoption rate of iOS5 has been very fast, at least when compared to Android ICS. You will always have users that are very slow to upgrade, however they seem to be the minority on iOS. If the numbers from the article are correct, you should be fine using iOS 5 for you app.
Look at statistics and judge for yourself if it is worth the effort.
For example:
http://www.14oranges.com/2012/03/ios-version-statistics-march-14th-2012/
http://pxldot.com/post/18754186750/ios-ebb-and-flow
from which I can read that < 11% are still using iOS 4.3
Or just search for e.g. "ios version stats", and try to find a web site that matches the target audience for your app.
This depends a lot on your app. But I would recommend supporting only iOS 5.0 and later because:
The new Xcode creates iOS 5.1 projects by default.
The new Xcode doesn't include iOS 4.3 simulator by default.
Apple has some iOS 5.0 only apps (like iTunes U).
So I guess, Apple is somehow pushing developers to support only the newer versions of the iOS.
Here is a good article that has some recent stats about iOS 5 adoption rates and good arguments on why to support only iOS 5 for new apps.
Here is another good article that discusses the question. Its conclusion is:
I think that both positions (support old, or support only new) are valid.
So it really depends on your special case. But personally, I'll currently support iOS 5.0 or later, unless there are solid reasons for a particular app.
I asked the same question some time ago and did not get any good answer with respect to a reliable up-to-date source of statistic data. In the end it comes down to your target market.
People who do not update their os recently are not likely to buy apps in high volumes. So even if these devices exist, the fraction of potential customers amongst their owners is most likely much smaller. That makes it hard to justify the extra effort in providing iOS 5.0+ functionaltiy and same functionality for smaller iOS.
On the other hand it may be suitable for you just to omit some functions for older iOS. That of course depends on the nature of the 5.0+ function that you want to use. Testing the curent os version and then deciding wether to call a function/method or not ist not that much of an effort. It needs to be tested though.
On the other hand there may be an interesting part of the user community that does consume apps but did not yet afford a brand new device. There is a number of devices around which cannot be migrated to iOS 5.x. And I personally would be interested in a) how many of these divices exist and b) how many of these are still in use.
If it is a new app then adressing older devices may not be justifyable. Unless of course you address some very special interest group and now for sure that the amount of oder devices is of a significant value.
Just some thoughts. Sorry that I did not have the statistics handy that you were looking for.
In my opinion it depends on which features of iOS 5.0 you need...
As example: in an application I need support for forward geocoding, available only in iOS 5.0 so I decided that the number of unsupported devices "cost" less then the effort to find a non apple library for forward geocoding ..
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Is there a logging framework for iOS that could aid developers in diagnosing app crashes?
You may like:
Lumberjack: stable and traditional
"It is similar in concept to other popular logging frameworks such as log4j, yet is designed specifically for Objective-C, and takes advantage of features such as multi-threading, grand central dispatch (if available), lockless atomic operations, and the dynamic nature of the Objective-C runtime."
LibComponentLogging: beautiful and hardcore, used by RestKit
"LibComponentLogging is a small logging library for Objective-C applications on Mac OS X and the iPhone OS which provides conditional logging based on log levels and log components. Additionally, different logging strategies can be used, e.g. writing log messages to a file or sending them to the system log, while using the same logging interface."
NSLogger: fancy with a dedicated visualization OS X App
"NSLogger is a high perfomance logging utility which displays traces emitted by client applications running on Mac OS X or iOS (iPhone OS). It replaces your usual NSLog()-based traces and provides powerful additions like display filtering, image and binary logging, traces buffering, timing information, etc."
I know this post is old but I'm looking for one as well. I found one called Lumberjack, though I haven't tried it yet.
I created a simple logging framework that might help. I'd appreciate any feedback you have. Hope it helps.
Link to Project Page
This previous question seems to overlap. But the bottom line is:
NSLog(#"message");
or:
printf("message");
I have a slightly different need: not only do I want to debug crashes, but I also need to debug other errors (NSError, NSException).
I tried all 3 packages mentioned in IlDan's answer. However, all of them require me to adopt a new way of logging, which may not be compatible with the libraries I depend on. For example, I intended to adopt NSLogger but RestKit, which is an important library in my project, uses LibComponentLogging.
So I ended up with writing a small pod (https://github.com/kennethjiang/Teleport-NSLog) for that. The mechanism is to redirect stderr (where NSLog + all these logging frameworks write messages to) to a backend HTTP server. Now I can debug my app running in user's device just as if it was running in my xcode. :)
For basic logging use NSLog(#"your message here")
If you want more flexible logging look into Lumberjack. It can let you disable logging in production etc etc.