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gavinhoward / bc

An implementation of the POSIX bc calculator with GNU extensions and dc, moved away from GitHub. Finished, but well-maintained.
https://git.gavinhoward.com/gavin/bc
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Improve Reproducibility (Reproducible Builds) #54

Closed pacordova closed 2 years ago

pacordova commented 2 years ago

On POSIX systems, find may have indeterministic output (I believe based on the inode on the filesystem). sort is needed to ensure the output is deterministic.

In my builds, this resulted in the build order in the generated Makefile changing around. Thus building on a fresh partition made with mkfs.ext4 would result in the binary being different each time. The compiled binary code in thebc binary shuffled around depending on which files were built first. Possibly the build order in the Makefile was affecting the order in which files were linked?

I added LC_ALL=C recommended by reproducible-builds.org. See below for reference:

gavinhoward commented 2 years ago

The only hangup I would have had is if the way you did it was not portable to POSIX sh. I consulted the standard, and your solution is portable!

I agree that reproducible builds are very important. So thank you for your contribution! I have accepted it, and it will be in the release out in a day or two. I just have to make sure everything builds correctly.

pacordova commented 2 years ago

No problem! Thank you for accepting my pull request! One additional comment: With this change I do get reproducible builds, although I do not use -flto Your recommended optimization of -O3 I think should be ok, but I do know that Link Time Optimization (LTO) and Profile Guided Optimization (PGO) can both potentially break build determinism. Either way the end user should be able get reproducible builds if they want it with this change. The CFLAGS I was testing with were CFLAGS='-march=x86-64 -pipe -Os -fstack-protector-strong -fstack-clash-protection' with GCC 11.2.0.

gavinhoward commented 2 years ago

Thank you!