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Patches to build rustc reproducibly.
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Reproducible rustc

This repository contains a proof of concept for building rustc reproducibly.

The patches it uses are not all completely clean or even correct; they are intended to serve as a basis for discussion. We would greatly appreciate any suggestions for how to improve them.

To get reproducible builds locally, either run or

  1. Apply the patches to two identical rustcs (tested with version 1.37.0).
  2. Build the two rustcs.
  3. Diff their stage 2s.


We currently require the following patches to build rustc reproducibly.

  • We can use the config option remap-debuginfo to pass --remap-path-prefix to rustc processes. As currently implemented, this does not work for non-target crate types such as proc-macro, which causes some libraries to depend on the path. We fix this by modifying it to work for everything.

  • We need to modify rustc to avoid hashing the --sysroot argument, which contains the current directory and so leads to non-reproducible builds when using different source paths.

  • We modify librustc_llvm to avoid using the __FILE__ macro, which can contain absolute paths. We do this by propagating NDEBUG from the bootstrap if applicable.

  • Similarly, we need to avoid using __FILE__ when compiling compiler-rt. This behavior cannot be disabled as easily as the one above, so as a hack we simply remove the __FILE__ macro.

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