[GHC] #9452: freeGroup: block size is zero

[GHC]

#9452: freeGroup: block size is zero
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              Reporter:              |            Owner:  simonmar
  scott.sadler                       |           Status:  new
                  Type:  bug         |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Runtime     |         Keywords:
  System                             |     Architecture:  x86_64 (amd64)
            Resolution:              |       Difficulty:  Unknown
      Operating System:  MacOS X     |       Blocked By:
       Type of failure:  Runtime     |  Related Tickets:
  crash                              |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by rwbarton):

 According to my reading of
 https://www.opengl.org/sdk/docs/man2/xhtml/glReadPixels.xml,
 `glReadPixels` with `format=GL_RGBA` and `type=GL_UNSIGNED_INT` will write
 one unsigned int per channel per pixel, so it will overwrite the array you
 allocated by a factor of 4. Looks like it is overwriting some GC
 information as `evacuate` and `freeGroup` are GC-related functions (not
 surprising that the GC would run during `peekArray`, as it has to allocate
 a large list).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9452#comment:1>
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