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XcodeDirectoryStructure.md

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Xcode.app Directory Structure

Xcode.app is huge! The installation size is more than 12GB as of Xcode 14.0, with millions of files in it. Most of time we can treat it as a black box, but sometimes we need to know where the important files are, e.g. system libraries/frameworks, especially when providing the search paths to compiler.

Here is an extremely simplified view to see where the common files are inside Xcode.app.1

Platforms

Platforms have the dynamic libraries/frameworks that are used at runtime.

$DEVELOPER_DIR/Platforms
├── iPhoneSimulator.platform
│  └── Developer
│      ├── usr/lib
│      │  ├── libXCTestBundleInject.dylib
│      │  ├── libXCTestSwiftSupport.dylib
│      │  └── XCTest.swiftmodule
│      ├── Library/Frameworks
│      │  └── XCTest.framework
│      └── SDKs/iPhoneSimulator.sdk
│         └── System/Library/Frameworks
│         │  ├── UIKit.framework
│         │  ├── Foundation.framework
│         │  └── ... (more system frameworks)
│         ├── /usr/lib
│         │  ├── libc++.tbd
│         │  ├── libobjc.tb
│         │  └── ... (more lib*.tb)
│         └── /usr/lib/swift
│            ├── Swift.swiftmodule
│            ├── libswiftCore.tbd
│            └── ... (more libswift*.tbd and *.swiftmodule)
├── iPhoneOS.platform
├── MacOSX.platform
└── ... (more platforms)

Compiler Flags

  • SDK path: -sdk $DEVELOPER_DIR/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk
  • System framework search path -F $DEVELOPER_DIR/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/System/Library/Frameworks
  • XCTest.framework search path -F $DEVELOPER_DIR/Platforms/iPhoneSimulator.platform/Developer/Library/Frameworks
  • XCTest swift support search path -I $DEVELOPER_DIR/Platforms/iPhoneSimulator.platform/Developer/usr/lib

Notes

  • XCTest.framework is at a special location. Unlike other frameworks, XCTest.framework shouldn't be linked in production.
  • Most system dylibs are actually .tbd instead of real binaries.

Toolchains

Toolchains contain the build tools, e.g. compiler, linker, and support static libraries at compile time.

$DEVELOPER_DIR/Toolchains/XcodeDefault.xctoolchain
├── usr/bin
│  ├── clang
|  ├── cc -> clang (symlink)
|  ├── c++ -> clang (symlink)
│  ├── swift-frontend
│  ├── swift -> swift-frontend (symlink)
│  ├── swiftc -> swift-frontend (symlink)
│  ├── swift-drivier
│  └── ...
├── usr/lib
│  └── ...
├── usr/lib/swift
│  ├── iphonesimulator
│  │  ├── libswiftCompatibility50.a
│  │  ├── libswiftCompatibility51.a
│  │  ├── libswiftCompatibilityConcurrency.a
│  │  ├── libswiftCompatibilityDynamicReplacements.a
│  │  └── ...
│  ├── iphoneos
│  └── ...
└── Developer/Platforms (only 3 platforms relevant to development)
   ├── iPhoneSimulator.platform
   ├── MacOSX.platform
   └── AppleTVSimulator.platform

Notes

  • $DEVELOPER_DIR/Toolchains/XcodeDefault.xctoolchain/usr/bin is where xcrun to locate tools.
  • swift and swiftc are just symlinks to swift-frontend.
  • clang++, c++, cc are symlinks to clang.

Footnotes

  1. DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer/ ↩