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MacOS Deployment

The macdeployqtplus script should not be run manually. Instead, after building as usual:

make deploy

When complete, it will have produced Bitcoin-Core.dmg.

SDK Extraction

Step 1: Obtaining Xcode.app

Our current macOS SDK (Xcode-12.1-12A7403-extracted-SDK-with-libcxx-headers.tar.gz) can be extracted from Xcode_12.1.xip. Alternatively, after logging in to your account go to 'Downloads', then 'More' and look for Xcode_12.1. An Apple ID and cookies enabled for the hostname are needed to download this. The sha256sum of the archive should be 612443b1894b39368a596ea1607f30cbb0481ad44d5e29c75edb71a6d2cf050f.

After Xcode version 7.x, Apple started shipping the Xcode.app in a .xip archive. This makes the SDK less-trivial to extract on non-macOS machines. One approach (tested on Debian Buster) is outlined below:

# Install/clone tools needed for extracting Xcode.app
apt install cpio
git clone https://github.com/bitcoin-core/apple-sdk-tools.git

# Unpack Xcode_12.1.xip and place the resulting Xcode.app in your current
# working directory
python3 apple-sdk-tools/extract_xcode.py -f Xcode_12.1.xip | cpio -d -i

On macOS the process is more straightforward:

xip -x Xcode_12.1.xip

Step 2: Generating Xcode-12.1-12A7403-extracted-SDK-with-libcxx-headers.tar.gz from Xcode.app

To generate Xcode-12.1-12A7403-extracted-SDK-with-libcxx-headers.tar.gz, run the script gen-sdk with the path to Xcode.app (extracted in the previous stage) as the first argument.

# Generate a Xcode-12.1-12A7403-extracted-SDK-with-libcxx-headers.tar.gz from
# the supplied Xcode.app
./contrib/macdeploy/gen-sdk '/path/to/Xcode.app'

Deterministic macOS DMG Notes

Working macOS DMGs are created in Linux by combining a recent clang, the Apple binutils (ld, ar, etc) and DMG authoring tools.

Apple uses clang extensively for development and has upstreamed the necessary functionality so that a vanilla clang can take advantage. It supports the use of -F, -target, -mmacosx-version-min, and -isysroot, which are all necessary when building for macOS.

Apple's version of binutils (called cctools) contains lots of functionality missing in the FSF's binutils. In addition to extra linker options for frameworks and sysroots, several other tools are needed as well such as install_name_tool, lipo, and nmedit. These do not build under Linux, so they have been patched to do so. The work here was used as a starting point: mingwandroid/toolchain4.

In order to build a working toolchain, the following source packages are needed from Apple: cctools, dyld, and ld64.

These tools inject timestamps by default, which produce non-deterministic binaries. The ZERO_AR_DATE environment variable is used to disable that.

This version of cctools has been patched to use the current version of clang's headers and its libLTO.so rather than those from llvmgcc, as it was originally done in toolchain4.

To complicate things further, all builds must target an Apple SDK. These SDKs are free to download, but not redistributable. To obtain it, register for an Apple Developer Account, then download Xcode_12.1.

This file is many gigabytes in size, but most (but not all) of what we need is contained only in a single directory:

Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk

See the SDK Extraction notes above for how to obtain it.

The Guix process build 2 sets of files: Linux tools, then Apple binaries which are created using these tools. The build process has been designed to avoid including the SDK's files in Guix's outputs. All interim tarballs are fully deterministic and may be freely redistributed.

xorrisofs is used to create the DMG.

xorrisofs cannot compress DMGs, so afterwards, the DMG tool from the libdmg-hfsplus project is used to compress it. There are several bugs in this tool and its maintainer has seemingly abandoned the project.

The DMG tool has the ability to create DMGs from scratch as well, but this functionality is broken. Only the compression feature is currently used. Ideally, the creation could be fixed and xorrisofs would no longer be necessary.

Background images and other features can be added to DMG files by inserting a .DS_Store during creation.

As of OS X 10.9 Mavericks, using an Apple-blessed key to sign binaries is a requirement in order to satisfy the new Gatekeeper requirements. Because this private key cannot be shared, we'll have to be a bit creative in order for the build process to remain somewhat deterministic. Here's how it works:

  • Builders use Guix to create an unsigned release. This outputs an unsigned DMG which users may choose to bless and run. It also outputs an unsigned app structure in the form of a tarball, which also contains all of the tools that have been previously (deterministically) built in order to create a final DMG.
  • The Apple keyholder uses this unsigned app to create a detached signature, using the script that is also included there. Detached signatures are available from this repository.
  • Builders feed the unsigned app + detached signature back into Guix. It uses the pre-built tools to recombine the pieces into a deterministic DMG.