On Mo, 12.04.21 20:40, Fedora Development ML (devel@xxxxxxxxxxxxxxxxxxxxxxx) wrote: > On Mon, 2021-04-12 at 15:46 -0400, Ben Cotton wrote: > > https://fedoraproject.org/wiki/Changes/Package_information_on_ELF_objects > > Putting packaging info into a binary guarantees that each successive > package containing ELF binaries will not contain exactly the same > binaries, even if there are no changes. > > Now, what I just wrote there is predicated on "reproducible builds" > where the same source (including deps, headers) and the same toolchain > produce the same output. This may or may not be a thing. My concern is > that we completely eliminate the possibility of binaries being > unchanged. I think this is a misunderstanding how reproducible builds are supposed to work. For example, consider $SOURCE_DATE_EPOCH as defined here: https://reproducible-builds.org/specs/source-date-epoch/ It's expressly defined to be used as the source timestamp when that source timestamp is included in build output. It also also expressly documented to be a value initialized from the packaging Changelog timestamps. Or in other words: the way the reproducible builds project understands their own stuff it's absolutely OK to generate different output on package rebuilds that change the package versions. Or in other words: packaging metadata are sources too. If they change (and a version bump constitutes a change) the output might change, and that's expected. What's key really is that the only things that can effect generated output are the build/packaging environment and the sources, but not parameters outside of that, such as the actual wallclock. > My concern centers around the Copy on Write (CoW) use case - when > packages are updated, some files changes, and some may stay the same. > Where they are the same, we can save I/O and possibly download time > long term. Reproducible builds the way they are defined do not address such file-level CoW optimization so much. They do address CoW optimization on a package level much more however: i.e. the same package build will have the same files in them, no matter what. Or to say this differently: if you want reproducible to work the way ou think it should work, you'd have to start by convincing the uptream maintainers to kill $SOURCE_DATE_EPOCH and similar concepts, but good luck with that. Lennart -- Lennart Poettering, Berlin _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam on the list, report it: https://pagure.io/fedora-infrastructure
