Xcode 5 and iOS 7 Architecture and Valid architectures

Question

I m starting new project in Xcode 5  I want to develop application using iOS SDK 7 but with deployment target iOS 5 0  As soon as I create new project in Xcode and try to change deployment target to 5 0  I ve got this message   Applications including an arm64 slice are not compatible with versions of iOS prior to 6 0 Adjust your Architectures build setting to not include arm64 in order to deploy to releases prior to iOS 6 0    So changed architectures to Standard  no 64bit   I compiles  runs but I do not really understand what just happend What s the difference between Architectures and Valid architectures settings in Xcode project Build Settings If I set Architectures to exclude 64-bit what happens when I run my app on 64-bit iPhone or iOS Simulator  I know it works  I m just curious what hapens underneath  Can you explain big mess with new 64-bit architecture

User · Accepted Answer

Set the architecture in build setting to Standard architectures(armv7,armv7s)

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iPhone 5S is powered by A7 64bit processor. From apple docs

Xcode can build your app with both 32-bit and 64-bit binaries included. This combined binary requires a minimum deployment target of iOS 7 or later.

Note: A future version of Xcode will let you create a single app that supports the 32-bit runtime on iOS 6 and later, and that supports the 64-bit runtime on iOS 7.

From the documentation what i understood is

Xcode can create both 64bit 32bit binaries for a single app but the deployment target should be iOS7. They are saying in future it will be iOS 6.0
32 bit binary will work fine in iPhone 5S(64 bit processor).

Update (Xcode 5.0.1)
In Xcode 5.0.1 they added the support to create 64 bit binary for iOS 5.1.1 onwards.

Xcode 5.0.1 can build your app with both 32-bit and 64-bit binaries included. This combined binary requires a minimum deployment target of iOS 5.1.1 or later. The 64-bit binary runs only on 64-bit devices running iOS 7.0.3 and later.

Update (Xcode 5.1)
Xcode 5.1 made significant change in the architecture section. This answer will be a followup for you. Check this

User · Answer

My understanding from Apple Docs    What is Architectures  ARCHS  into Xcode build-settings   Specifies architecture s to which the binary is TARGETED  When specified more that one architecture  the generated binary may contain object code for each of the specified architecture   What is Valid Architectures  VALID ARCHS  into Xcode build-settings    Specifies architecture s for which the binary may be BUILT  During build process  this list is intersected with ARCHS and the resulting list specifies the architectures the binary can run on   Example  - One iOS project has following build-settings into Xcode    ARCHS   armv7 armv7s VALID ARCHS   armv7 armv7s arm64 In this case  binary will be built for armv7 armv7s arm64 architectures  But the same binary will run on ONLY ARCHS   armv7 armv7s

User · Answer

Simple fix   Targets -  Build Settings -  Build Options -  Enable Bitcode -  No  Works on device with iOS 9 3 3

User · Answer

You do not need to limit your compiler to only armv7 and armv7s by removing arm64 setting from supported architectures  You just need to set Deployment target setting to 5 1 1  Important note  you cannot set Deployment target to 5 1 1 in Build Settings section because it is drop-down only with fixed values  But you can easily set it to 5 1 1 in General section of application settings by just typing the value in text field

User · Answer

None of the answers worked and then I was forgetting to set minimum deployment target which can be found in Project -  General -  Deployment Info -  Deployment Target -  8 0

User · Answer

When you set 64-bit the resulting binary is a  Fat  binary  which contains all three Mach-O images bundled with a thin fat header  You can see that using otool or jtool  You can check out some fat binaries included as part of the iOS 7 0 SDK  for example the AVFoundation Framework  like so     cd   Developer Platforms iPhoneOS platform DeviceSupport 7 0    11A465   Symbols System Library Frameworks AVFoundation framework    otool -V -f AVFoundation                                                                     9 36 Fat headers fat magic FAT MAGIC nfat arch 3 architecture arm64       The 64-bit version  A7      cputype CPU TYPE ARM64     cpusubtype CPU SUBTYPE ARM64 ALL     capabilities 0x0     offset 16384     size 2329888     align 2 14  16384  architecture armv7          A5X - packaged after the arm64version     cputype CPU TYPE ARM     cpusubtype CPU SUBTYPE ARM V7     capabilities 0x0     offset 2359296     size 2046336     align 2 14  16384  architecture armv7s         A6 - packaged after the armv7 version     cputype CPU TYPE ARM     cpusubtype CPU SUBTYPE ARM V7S     capabilities 0x0     offset 4407296     size 2046176     align 2 14  16384    As for the binary itself  it uses the ARM64 bit instruction set  which is  mostly compatible with 32-bit  but  a totally different instruction set  This is especially important for graphics program  using NEON instructions and registers   Likewise  the CPU has more registers  which makes quite an impact on program speed  There s an interesting discussion in http   blogs barrons com techtraderdaily 2013 09 19 apple-the-64-bit-question  mod yahoobarrons on whether or not this makes a difference  benchmarking tests have so far clearly indicated that it does   Using otool -tV will dump the assembly  if you have XCode 5 and later   and then you can see the instruction set differences for yourself  Most  but not all  developers will remain agnostic to the changes  as for the most part they do not directly affect Obj-C  CG  APIs notwithstanding   and have to do more with low level pointer handling  The compiler will work its magic and optimizations

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