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

[GHC]

#9452: freeGroup: block size is zero
----------------------------------+----------------------------------------
       Reporter:  scott.sadler    |                   Owner:  simonmar
           Type:  bug             |                  Status:  new
       Priority:  normal          |               Milestone:
      Component:  Runtime System  |                 Version:  7.8.3
       Keywords:                  |        Operating System:  MacOS X
   Architecture:  x86_64 (amd64)  |         Type of failure:  Runtime crash
     Difficulty:  Unknown         |               Test Case:
     Blocked By:                  |                Blocking:
Related Tickets:                  |  Differential Revisions:
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 I'm trying to extract pixels from OpenGL and read them into a
 ForeignPointer, but getting a segfault while doing a peek operation.

 The fault is on line 240 in `peekArray`. It crashes in different ways
 depending on the arguments to `readPixelArray`.

 with `readPixelArray 0 0 100 100`:

 {{{
 (lldb) run
 Process 26467 launched: '/Users/scott/Code/grids/dist/build/grids/grids'
 (x86_64)
 0x00000001015b3010
 Process 26467 stopped
 * thread #1: tid = 0x23d3cc, 0x0000000100621ead grids`evacuate + 157,
 queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1,
 address=0xfffffffffffffff8)
     frame #0: 0x0000000100621ead grids`evacuate + 157
 grids`evacuate + 157:
 -> 0x100621ead:  movl   -0x8(%r12), %esi
    0x100621eb2:  leal   -0x1(%rsi), %ecx
    0x100621eb5:  cmpl   $0x3b, %ecx
    0x100621eb8:  ja     0x1006222a9               ; evacuate + 1177
 }}}

 with `readPixelArray 0 0 200 200`:

 (lldb) run
 Process 26647 launched: '/Users/scott/Code/grids/dist/build/grids/grids'
 (x86_64)
 0x00000001095d8010
 grids: internal error: freeGroup: block size is zero
     (GHC version 7.8.3 for x86_64_apple_darwin)
     Please report this as a GHC bug:
 http://www.haskell.org/ghc/reportabug
 Process 26647 stopped
 * thread #1: tid = 0x23f4d4, 0x00007fff8b2cc866
 libsystem_kernel.dylib`__pthread_kill + 10, queue = 'com.apple.main-
 thread', stop reason = signal SIGABRT
     frame #0: 0x00007fff8b2cc866 libsystem_kernel.dylib`__pthread_kill +
 10
 libsystem_kernel.dylib`__pthread_kill + 10:
 -> 0x7fff8b2cc866:  jae    0x7fff8b2cc870            ; __pthread_kill + 20
    0x7fff8b2cc868:  movq   %rax, %rdi
    0x7fff8b2cc86b:  jmpq   0x7fff8b2c9175            ; cerror_nocancel
    0x7fff8b2cc870:  ret

 The "freeGroup: block size is zero" message appears in the second output.

 I'm stumped trying to debug this one. I didn't get as far as trying to go
 backwards in time debugging it because of lack of familiarity with lldb.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9452>
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