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Sarah Jamie Lewis 2023-07-13 12:24:01 -07:00
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blog/2023-07-14-cwtch-ui-reproducible-builds.md
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@ -43,9 +43,28 @@ For reproducible linux builds we had to modify the generated `linux/CMakeLists.t
* `--hash-style=gnu` - asserts a standard hashing scheme to use across all compiled artifacts. Without this compilers that have been compiled with different default schemes will produce different artifacts
* `--build-id=none` - suppresses build id generation. Without this each compiled artifact will have a section of effectively randomized data.
We also define a new [link script](https://git.openprivacy.ca/cwtch.im/cwtch-ui/src/commit/3148a8e0642e51bc59d9eb00ca2b319a7097285a/elf_x86_64.x) that differs from the default by removing all `.comment` sections from object files. We do this because the linking process links in non-project artifacts like `crtbeginS.o` which, in most systems, us compiled with a `.comment` section (the default linking script already removes the `.note.gnu*` sections.
### Tar Archives
Finally, following the [guide at https://reproducible-builds.org/docs/archives/](https://reproducible-builds.org/docs/archives/) we defined standard metadata for the generated Tar archives to make them also reproducible.
## Limitations and Next Steps
The above changes mean that official linux builds of the same commit will now result in identical artifacts. We have also produced a repliqate script
However, because repliqate is based on Debian images and our official builds are based on an Ubuntu distribution the resulting archives differ by a single instruction at the start of a few sections - introduced because Ubuntu compiles and provides C Runtime (CRT) artifacts (e.g. `crti.o` with full branch protection enabled. On 64-bit systems this results in an `endcr64` instruction being inserted at the start of the `.init` and `.fini` sections, among others.
In order to allow people to fully repliqate Cwtch builds in an isolated environment like repliqate, as we do for Cwtch Bindings, it will be necessary to provide instructions for setting up a hardened image that can work the same way in repliqate.
### Pinned Dependencies
While our repliqate scripts pin several major dependencies like flutter and go, and the dependencies managed by these systems are locked to specific versions, there are still a few dependencies within the ecosystems that are not strictly pinned.
The major one is libc. Operating systems rarely make big changes to packaged libc versions for a specific distribution (typically because doing so in a non-breaking way would be a major undertaking).
However this does mean that Cwtch reproduciblility is implicitly tied to operating system practices - this is something we would like to begin decoupling ourselves from.
## Help us go further!
We couldn't do what we do without all the wonderful community support we get, from [one-off donations](https://openprivacy.ca/donate) to [recurring support via Patreon](https://www.patreon.com/openprivacy).