[GHC] #7790: Add dummy undefined symbols to indicate ways

[GHC]

#7790: Add dummy undefined symbols to indicate ways
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Reporter:  ezyang            |          Owner:  ezyang          
    Type:  task              |         Status:  new             
Priority:  normal            |      Component:  Compiler        
 Version:                    |       Keywords:                  
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
 Failure:  None/Unknown      |      Blockedby:                  
Blocking:                    |        Related:                  
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 Currently, "way" information is not recorded into object files; it is only
 recorded into 'hi' files.  This means if you are using, say, rts/Linker.c
 (say, if you're GHCi or a dynamic plugins package), if you mess up and
 load an object file compiled the wrong way, you will be very sad.

 I think a cute trick we could play is to define a bunch of dummy symbols
 per-way, and add them as undefined symbols to objects, to indicate what
 way they were compiled, e.g. with the `-u` linker flag.  Various RTS's
 export the symbols of ways they support, and attempting to link an object
 with an incompatible RTS results in a link error.

 Are there any problems with this scheme? If not, I'll go ahead and
 implement it.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7790>
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