[GHC] #12935: Object code produced by GHC is non-deterministic

[GHC]

#12935: Object code produced by GHC is non-deterministic
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nh2):

 I have attached some files, `objdump-headers-1.txt` and `objdump-
 headers-1.txt` which are the outputs of `objdump --all-headers Example.o`
 as produced by `ghc --make -j1` of a project of mine.

 Have a look at them in a diff viewer.

 At the top you will find probably what was talked about before: Uniques
 making it into symbol names, like `cZoQ_info` vs `cQJU_info`.

 But further down you see

 {{{
 0000000000002f10 R_X86_64_PC32     .data.rel.ro+0x00000000000000e8
 }}}

 vs

 {{{
 0000000000002f10 R_X86_64_PC32     .data.rel.ro+0x00000000000000f0
 }}}

 which is the result of some values in the `RELOCATION RECORDS FOR
 [.data.rel.ro]` having their positions swapped:

 {{{
 0000000000000100 R_X86_64_64
 monozmtraversablezm1zi0zi2zi1zm4aNtRX1lKHJF1rNRp4LmtV_DataziMonoTraversable_zdfMonoFoldableZMZN_closure
 0000000000000108 R_X86_64_64
 monozmtraversablezm1zi0zi2zi1zm4aNtRX1lKHJF1rNRp4LmtV_DataziMonoTraversableziUnprefixed_any_closure
 }}}

 vs

 {{{
 0000000000000100 R_X86_64_64
 monozmtraversablezm1zi0zi2zi1zm4aNtRX1lKHJF1rNRp4LmtV_DataziMonoTraversableziUnprefixed_any_closure
 0000000000000108 R_X86_64_64
 monozmtraversablezm1zi0zi2zi1zm4aNtRX1lKHJF1rNRp4LmtV_DataziMonoTraversable_zdfMonoFoldableZMZN_closure
 }}}

 These are the same things, they have exactly the same symbol names, just
 their order swapped.

 How might this happen?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12935#comment:6>
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