CoderLyn's developer journey

Understanding binaries when archiving a build - WIP

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Lyn Tee
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4 min read

Steps in releasing an app

  1. Build on your local machine with Xcode

    • You need to select a specific device when doing this
    • The build is compiled for this device and its CPU / architecture (e.g. ARM 64 bit, Intel x86 64 bit, ARM 32 bit etc)

  2. Archive a build

    • There are three components to archiving a build
      • Create the required binaries
      • Signing keys
      • Provisioning profiles

Let's talk just about creating the required binaries.

Whenever Xcode compiles and builds, it is compiling the language into binary. It goes from interpretive language (e.g. Swift) > machine code > binary

  • Native code sits somewhere in this spectrum.. not sure where. Maybe at machine code?

Binaries are tailored to the device's CPU. We need a different binary for each different CPU type. Why?

  • Native code is read differently

Frameworks / Libraries / SDKs

If any of these are written in native code (aka C, C#, C++) then the SDK must provide different pre-compiled versions for each of the supported CPUs.

If the SDK doesn't support a CPU, then if you import that library into your code, you will not be able to support that CPU either.

Digression into CPU types

Common CPU types (also called architecture)

  • ARM 32 bit (ARM is a company, like Intel is a company)
  • ARM 64 bit
  • x86 64 bit (Intel)

Some background on ARM and Intel:

  • All Android devices were and are built on ARM
  • iOS was built on Intel in the early days. At some stage, maybe iPhone 5 or 6, Apple switched to ARM as ARM is believed to be faster for mobile devices

Some background on 32 vs 64 bits

  • 64 bits can run 32 bits. However Apple have stopped making 64 bits backward compatible as a design choice for some of the laptops, ie M1
  • 32 bits cannot run 64 bits
    • Think of it this way: a 32 bit integer has less information than a 64 bit integer. So a 64 bit can load a 32 bit integer with no issues.
    • However a 32 bit integer cannot load a 64 bit integer.

IPA

  • All files you need to run an appilcation
  • Inside the binary there is a full file structure like images, code, icons
  • Is an IPA a binary then?
  • This ensures that the build is compiled for all possible devices. Different devices can have different architectures.

Raw notes

Binary

  • [ ] 0s and 1s
  • [ ] A file that’s no longer machine readable, and now it’s machine language
  • [ ] Compiling the language into a binary

Build vs app store ready

  • [ ] Build is for one specific device
  • [ ] Different devices have different CPU architecture
    • [ ] 64 bit
    • [ ] 32
    • [ ] ARM - different way of doing CPU: ARM64 apple is the apple 64 bit architectyure. ARM is a seperate company that Apple have chosen to use over Intel now. Theoretically ARM is optimised for mobile, and mobile phones have used ARM for a long time. Android have always used ARM, iOS used Intel until iphone 5 or 6 then switched.
    • [ ] Intel: x86_64 is the Intel 64 bit architecture
    • [ ]
    • [ ] So how the logic inside the board works and how it interprets commands

Librairies are pre-compiled and specifyt eharchitecture they support

Unit tests are run on local machine, not through the simulator

Different architecturs in fraemworks are only important for C code / C# / C++. Anything that comiples to native code.

  • [ ] With C, need to have compiled versio for te the CPU
    • [ ] C code is called NATIVE to the CPU. It’s not just C code that is native to the CPU. BUT C is often the same.
    • [ ] C is the language you write that copmiles to native code
    • [ ]
  • [ ] Wihtout C code

Java run time

  • [ ] run time is the native code interpretaion
  • [ ] Java doesn’t need to comiple down to native code because it runs in runtime
  • [ ] Run time deals with the cpu

If any libraries use native code (vs interprative languages), they will need to specifiy the different architecutres

  • [ ] Native code (C, C#, C++) is much faster than interprative languages (e.g. swift)
  • [ ]

Binary Next step up is machine code

Xcode