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diff --git a/doc/README_osx.txt b/doc/README_osx.txt new file mode 100644 index 0000000000..6eae4f5cf1 --- /dev/null +++ b/doc/README_osx.txt @@ -0,0 +1,71 @@ +Deterministic OSX Dmg Notes. + +Working OSX DMG's are created in Linux by combining a recent clang, +the Apple's 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 --sysroot, which are all necessary +when building for OSX. A pre-compiled version of 3.2 is used because it was not +available in the Precise repositories at the time this work was started. In the +future, it can be switched to use system packages instead. + +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: +https://github.com/mingwandroid/toolchain4 + +In order to build a working toolchain, the following source packages are needed +from Apple: cctools, dyld, and ld64. + +Beware. This part is ugly. Very very very ugly. In the future, this should be +broken out into a new repository and cleaned up. Additionally, the binaries +only work when built as x86 and not x86_64. This is an especially nasty +limitation because it must be linked with the toolchain's libLTO.so, meaning +that the entire toolchain must be x86. Gitian x86_64 should not be used until +this has been fixed, because it would mean that several native dependencies +(openssl, libuuid, etc) would need to be built as x86 first. + +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 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 a developer account, then download xcode_3.2.6_and_ios_sdk_4.3.dmg: +https://developer.apple.com/devcenter/download.action?path=/Developer_Tools/xcode_3.2.6_and_ios_sdk_4.3__final/xcode_3.2.6_and_ios_sdk_4.3.dmg +This file is several gigabytes in size, but only a single .pkg file inside is +needed (MacOSX10.6.pkg). From Linux, 7-zip can be used to extract this file. +The DMG can then be discarded. + +The gitian descriptors 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 Gitian's outputs. All interim tarballs are +fully deterministic and may be freely redistributed. + +genisoimage is used to create the initial DMG. It is not deterministic as-is, +so it has been patched. A system genisoimage will work fine, but it will not +be deterministic because the file-order will change between invocations. +The patch can be seen here: +https://raw.githubusercontent.com/theuni/osx-cross-depends/master/patches/cdrtools/genisoimage.diff +No effort was made to fix this cleanly, so it likely leaks memory badly. But +it's only used for a single invocation, so that's no real concern. + +genisoimage 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. It has been forked +and is available (with fixes) here: https://github.com/theuni/libdmg-hfsplus . + +The 'dmg' tool has the ability to create DMG's from scratch as well, but this +functionality is broken. Only the compression feature is currently used. +Ideally, the creation could be fixed and genisoimage would no longer be necessary. + +Background images and other features can be added to DMG files by inserting a +.DS_Store before creation. The easiest way to create this file is to build a +DMG without one, move it to a device running OSX, customize the layout, then +grab the .DS_Store file for later use. That is the approach taken here. |