[GHC] #7794: GHCi "Prelude.undefined" exceptions on ARM; ByteCodeItbls.mkJumpToAddr unimplemented

[GHC]

#7794: GHCi "Prelude.undefined" exceptions on ARM; ByteCodeItbls.mkJumpToAddr
unimplemented
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        Reporter:  cjwatson    |            Owner:
            Type:  bug         |           Status:  new
        Priority:  normal      |        Milestone:  7.8.1
       Component:  GHCi        |          Version:  7.6.2
      Resolution:              |         Keywords:
Operating System:  Linux       |     Architecture:  arm
 Type of failure:  GHCi crash  |       Difficulty:  Unknown
       Test Case:              |       Blocked By:
        Blocking:              |  Related Tickets:
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Comment (by RoboTux):

 Replying to [comment:6 cjwatson]:
 >
 > It will be called every time one of the generated chunks of code is
 called, so I would expect it to be suboptimal, yes.  That in itself might
 be tolerable.
 >
 > Much more importantly, though, this patch misses the point of flushing
 the instruction cache.  The point is that we need to flush the cache in
 order for the processor to reliably read back the code that we just
 > wrote out; flushing the cache in that very code is not a viable approach
 to that, because the cache-flushing code itself might not be read.  So I'm
 afraid I don't think this is going to work properly.  It might work some
 of the time, of course, depending on cache locality, but I can't see how
 it would work reliably.

 Oh, I didn't realize this was the generated code. I don't know if
 it's because of the language but I can't make much sense of what the code
 is
 doing. I assumed this code was some jit compiler and that the jump was
 executed when a function has just been compiled in order to actually call
 that
 function. If it's part of the generated function indeed it's very
 suboptimal
 and won't work as you very well explained.

 My apologize but I don't think I can bring this further without investing
 quite some time to understand the code.

 Thanks for being so quick in looking at the patch.

 Best regards.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7794#comment:7>
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