build_ios_app

Build iOS App without Xcode

This topic demonstrates how to build and debug an iOS app without an IDE or a build system.

cd llios/build_ios_app
./build.sh [--device] [--release]   # build the iOS app
./launch.sh  # launch the app in the simulator or device
./debug.sh   # launch the app and attach lldb to it

The demonstration includes

• building static libraries
• building Swift and Objective-C dynamic libraries
• building an executable
• packaging an app bundle
• code signing
• attaching lldb to the app
• launching an app in a simulator or a device

Screenshots

Simulator	Device

Toolchain

swiftc

-c (-emit-object)

Generate a object file.

-emit-library

Directly Generate a dynamic library.

-wmo (-whole-module-optimization)

Here is the Apple's words for WMO. WMO can take multiple source files and generate one object. Because of this, -wmo doesn't work with some other flags. For example, with --index-store-path it will yield error "index output filenames do not match input source files".

swiftc -wmo -o one.o source1.swift source2.swift

-incremental

-incremental is the opposite to -wmo. It generates each a .o file for every .swift source file. -incremental requires an output file map provided by -output-file-map.

{
  "": {
    "swift-dependencies": "Build/StatiLib-master.swiftdeps"
  },
  "Sources/StaticLib/foo.swift": {
    "dependencies": "Build/foo.d",
    "diagnostics": "Build/foo.dia",
    "llvm-bc": "Build/foo.bc",
    "object": "Build/foo.o",
    "swift-dependencies": "Build/foo.swiftdeps",
    "swiftmodule": "Build/foo~partial.swiftmodule"
  },
  "Sources/StaticLib/bar.swift": {
    ...
  }
}

The swift driver with -incremental calls swift frontend with -primary-file for each source file and at the end it merges the module. (-primary-file is a frontend flag, which cannot be passed directly swift driver.)

> swiftc -incremental -output-file-map output_file_map.json Sources/StaticLib/bar.swift Sources/StaticLib/foo.swift -###

swiftc -frontend -c -primary-file Sources/StaticLib/bar.swift Sources/StaticLib/foo.swift -emit-module-path Build/bar.swiftmodule -parse-as-library -module-name StaticLib -o Build/bar.o
swiftc -frontend -c Sources/StaticLib/bar.swift -primary-file Sources/StaticLib/foo.swift -emit-module-path Build/foo.swiftmodule -parse-as-library -module-name StaticLib -o Build/foo.o
swiftc -frontend -merge-modules -emit-module Build/bar.swiftmodule Build/foo.swiftmodule -parse-as-library -module-name StaticLib -o Build/StaticLib.swiftmodule

-parse-as-library

Parse the input file(s) as libraries, not scripts. Without this, swiftc generates the main method for each compilation unit.

ld

-install_name

Install name, which is unique on Darwin platform, provides a dylib search path. It's set by passing -install_name to the linker (ld) when building a dylib (not an executable). In other words, install name is an attribute of a dylib itself. When -install_name path/to/DynamicLib.dylib is given, it ends up to a load command (LC_ID_DYLIB) in the dylib's macho-o load section.

Load command 3
          cmd LC_ID_DYLIB
      cmdsize 56
         name path/to/DynamicLib.dylib (offset 24)
   time stamp 1 Wed Dec 31 16:00:01 1969
      current version 0.0.0
compatibility version 0.0.0

When linking againt a dylib, a different load command (LC_LOAD_DYLIB) was added to the executable.

Load command 12
          cmd LC_LOAD_DYLIB
      cmdsize 56
         name path/to/DynamicLib.dylib (offset 24)
   time stamp 2 Wed Dec 31 16:00:02 1969
      current version 0.0.0
compatibility version 0.0.0

The install name can start with @executable_path, @loader_path, or @rpath, to provide a relative search path.

Note: -install_name is a linker flag. If calling from swift driver, we need to use -Xlinker.

Learn more

• Mach-O linking and loading tricks

libtool

Unlike -emit-library, I didn't find a flag for building a static library, so we need to use libtool -static to create a static library.

codesign

# Sign an apple bundle
codesign --force --sign {identity} Build/SampleApp.app
# Show signing info
codesign -vvvvv -d Build/SampleApp.app
# Verify signing
codesign -v --verify Build/SampleApp.app

simctl

xcrun simctl shutdown all
xcrun simctl boot "iPhone 12"
xcrun simctl install booted "Build/SampleApp.app"
xcrun simctl launch booted "me.qyang.SampleApp"