[GHC] #9003: GHC eventlog: thread stop status codes modified (breaking ghc-events, threadscope, edentv)

[GHC]

#9003: GHC eventlog: thread stop status codes modified (breaking ghc-events,
threadscope, edentv)
-------------------------------------------+-------------------------------
       Reporter:  jberthold                |             Owner:  simonmar
           Type:  bug                      |            Status:  new
       Priority:  normal                   |         Milestone:  7.8.3
      Component:  Runtime System           |           Version:  7.8.2
       Keywords:                           |  Operating System:
   Architecture:  Unknown/Multiple         |  Unknown/Multiple
     Difficulty:  Easy (less than 1 hour)  |   Type of failure:  Other
     Blocked By:                           |         Test Case:
Related Tickets:                           |          Blocking:
-------------------------------------------+-------------------------------
 A  patch in GHC-7.7 modified the "thread stop status" encoding, so the
 current ghc-events (version 0.4.2.0 from 2012) produces wrong stop reasons
 when reading an eventlog written by GHC-7.8.2.

 The GHC patch is
 http://git.haskell.org/ghc.git/commit/70e20631742e516c6a11c3c112fbd5b4a08c15ac
 The MVarRead block reason was added in the middle, shifting all following
 block reason codes one up.

 The error can be observed when a thread blocks on a black hole during a
 program run. Attached is a small test program which produces this
 situation, and two event logs for the same program run with the same
 arguments and RTS parameters. The program's two threads evaluate the same
 data, the parent thread typically blocks on a blackhole created by a
 forked child thread. Note the sequence around user event "child": The log
 written by GHC-7.6.3 correctly shows blocking on a black hole, while the
 log written by GHC-7.8.2 claims the main thread blocks "on I/O read".

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9003>
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