[tor-bugs] #32053 [Applications/Tor Browser]: macOS bundles for Tor Browser 9.0a8 are not reproducible

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#32053: macOS bundles for Tor Browser 9.0a8 are not reproducible
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 Reporter:  gk                                   |          Owner:  tbb-
                                                 |  team
     Type:  defect                               |         Status:  new
 Priority:  Immediate                            |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Critical                             |     Resolution:
 Keywords:  TorBrowserTeam201910, tbb-9.0-must,  |  Actual Points:
  tbb-9.0-issues, tbb-regression, tbb-9.0.1-can  |
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by alexcrichton):

 *.bc.z files in archives are a semi-custom compression format for LLVM IR
 files (we really should just use `*.gz`...) The `*.o` files are the
 codegen'd versions of those. Given that the LLVM IR is changing that means
 one of a few things:

 * Something in the source is changing, causing different IR to be produced
 * Rustc is non-deterministically producing IR
 * LLVM is non-deterministically optimizing IR

 It's great to narrow this down to just one crate! I've found that
 minimization tends to make bisection much much easier. Given that this is
 related to rlibs this probably isn't related to LTO since those object
 files are all pre-LTO. In terms of minimizing this further, are the object
 files similarly named? If so are there "obvious diffs" within them?
 Otherwise if the object files have completely different names that'd be
 more worrisome!

 If you can I'd recommend whacking away at the `style` crate's source code,
 deleting swaths of it as you can to see if you can get non-reproducible
 builds on one compiler. Basically at this point it's just a game of
 minimization to find the bug. If you've got a set of semi-digestable
 instructions to reproduce where you're at as well, we could try to pass
 this around and see if others can help chip in too to diagnose the bug.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32053#comment:11>
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