[GHC] #14713: GHCi doesn't load project.

[GHC]

#14713: GHCi doesn't load project.
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        Reporter:  recursion-ninja   |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.6.1
       Component:  GHCi              |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:  x86_64
                                     |  (amd64)
 Type of failure:  GHCi crash        |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by quasicomputational):

 Note that `numStates_g` is declared `extern` in `ukkCheckPoint.c` via
 `ukkCommon.h`, and is actually defined in `ukkCommon.c`. If we inspect the
 command line passed to GHC, we see that `ukkCheckPoint.o` appears before
 `ukkCommon.o`. Reducing to a tiny example, we can reproduce the bug:

 {{{
 $ cat a.c
 int numStates_g = 42;
 $ cat b.c
 extern int numStates_g;

 int foo(int a) {
   return a + numStates_g;
 }
 $ gcc -c a.c
 $ gcc -c b.c
 $ ghc --interactive a.o b.o
 GHCi, version 8.4.2: http://www.haskell.org/ghc/  :? for help
 Prelude> :q
 Leaving GHCi.
 $ ghc --interactive b.o a.o
 GHCi, version 8.4.2: http://www.haskell.org/ghc/  :? for help
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.4.2 for i386-unknown-linux):
         Loading temp shared object failed: /tmp/ghc12016_0/libghc_1.so:
 undefined symbol: numStates_g

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 So GHCi is sensitive to the ordering of `.o` files passed on the command
 line. This is already known as #13786, so I guess this issue's a
 duplicate.

 I've verified that the reproduction repo works with GHCi if the
 definitions are moved into `ukkCheckPoint.c`, which is a work-around.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14713#comment:5>
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