[GHC] #9741: Interpreter stack checks are not quite right

29 Oct 2014

      #9741: Interpreter stack checks are not quite right
-------------------------------------+-------------------------------------
       Reporter:  simonpj            |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.8.3
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
 In my experimental branch, I'm getting this failure on
 `tests/ghci/should_run/ghcirun002`:
 {{{
 <interactive>: internal error: ASSERTION FAILED: file rts/Interpreter.c,
 line 778

     (GHC version 7.9.20141029 for x86_64_unknown_linux)
 }}}

 The ASSERTION failure means that I must have `-DDEBUG` in my RTS; I have
 no idea why.  My `validate.mk` looks like this:
 {{{
 GhcStage1HcOpts += -ticky  -DDEBUG
 GhcStage2HcOpts +=  -ticky
 GhcLibHcOpts +=  -Wwarn -ticky
 SplitObjs       = YES
 }}}
 That is mysterious but not the main point.  Somehow we are getting a stack
 overflow in the interpreter.

 So I added this line to `Interpreter` on line 772:
 {{{
         debugBelch ( "Interpreter Sp=%p SpLim=%p headroom = %ld\n\n", Sp,
 SpLim, Sp-SpLim ) ;
 }}}
 Sure enough, when running test `ghcirun002` on HEAD, I get this output
 {{{
 Interpreter Sp=0x7f42649d0228 SpLim=0x7f42649d00c0 headroom = 45
 Interpreter Sp=0x7f42649d0228 SpLim=0x7f42649d00c0 headroom = 45
 Interpreter Sp=0x7f42649d0228 SpLim=0x7f42649d00c0 headroom = 45
 Interpreter Sp=0x7f42649d0238 SpLim=0x7f42649d00c0 headroom = 47
 Interpreter Sp=0x7f42649d0228 SpLim=0x7f42649d00c0 headroom = 45
 Interpreter Sp=0x7f42649d0228 SpLim=0x7f42649d00c0 headroom = 45
 Interpreter Sp=0x7f42649d0228 SpLim=0x7f42649d00c0 headroom = 45
 Interpreter Sp=0x7f42649d0228 SpLim=0x7f42649d00c0 headroom = 45
 Interpreter Sp=0x7f42649d0228 SpLim=0x7f42649d00c0 headroom = 45
 Interpreter Sp=0x7f42649d0210 SpLim=0x7f42649d00c0 headroom = 42
 Interpreter Sp=0x7f4264b40230 SpLim=0x7f4264b400c0 headroom = 46
 Interpreter Sp=0x7f42649e1230 SpLim=0x7f42649e10c0 headroom = 46
 Interpreter Sp=0x7f42649d9230 SpLim=0x7f42649d90c0 headroom = 46
 Interpreter Sp=0x7f4264182230 SpLim=0x7f42641820c0 headroom = 46
 Interpreter Sp=0x7f426417a230 SpLim=0x7f426417a0c0 headroom = 46
 Interpreter Sp=0x7f4264172230 SpLim=0x7f42641720c0 headroom = 46
 Interpreter Sp=0x7f426416a230 SpLim=0x7f426416a0c0 headroom = 46
 Interpreter Sp=0x7f4264162230 SpLim=0x7f42641620c0 headroom = 46
 Interpreter Sp=0x7f426415a230 SpLim=0x7f426415a0c0 headroom = 46
 Interpreter Sp=0x7f4264152230 SpLim=0x7f42641520c0 headroom = 46
 Interpreter Sp=0x7f426414a230 SpLim=0x7f426414a0c0 headroom = 46
 Interpreter Sp=0x7f4264142230 SpLim=0x7f42641420c0 headroom = 46
 Interpreter Sp=0x7f426413a230 SpLim=0x7f426413a0c0 headroom = 46
 Interpreter Sp=0x7f4264132230 SpLim=0x7f42641320c0 headroom = 46
 Interpreter Sp=0x7f42649d0238 SpLim=0x7f42649d00c0 headroom = 47
 Interpreter Sp=0x7f4264a1e238 SpLim=0x7f4264a1e0c0 headroom = 47
 Interpreter Sp=0x7f4264a16238 SpLim=0x7f4264a160c0 headroom = 47
 Interpreter Sp=0x7f4264a0e238 SpLim=0x7f4264a0e0c0 headroom = 47
 Interpreter Sp=0x7f4264a06238 SpLim=0x7f4264a060c0 headroom = 47
 Interpreter Sp=0x7f4257ff8238 SpLim=0x7f4257ff80c0 headroom = 47
 Interpreter Sp=0x7f4257ff0238 SpLim=0x7f4257ff00c0 headroom = 47
 Interpreter Sp=0x7f4257fe8238 SpLim=0x7f4257fe80c0 headroom = 47
 Interpreter Sp=0x7f4257fe0238 SpLim=0x7f4257fe00c0 headroom = 47
 Interpreter Sp=0x7f4257fd8238 SpLim=0x7f4257fd80c0 headroom = 47
 Interpreter Sp=0x7f4257fd0238 SpLim=0x7f4257fd00c0 headroom = 47
 Interpreter Sp=0x7f4257fc8238 SpLim=0x7f4257fc80c0 headroom = 47
 Interpreter Sp=0x7f4257fc0238 SpLim=0x7f4257fc00c0 headroom = 47
 Interpreter Sp=0x7f4257fb8238 SpLim=0x7f4257fb80c0 headroom = 47
 Interpreter Sp=0x7f4257fb0238 SpLim=0x7f4257fb00c0 headroom = 47
 Interpreter Sp=0x7f42641f8238 SpLim=0x7f42641f80c0 headroom = 47
 Interpreter Sp=0x7f42641f0238 SpLim=0x7f42641f00c0 headroom = 47
 Interpreter Sp=0x7f42644f8238 SpLim=0x7f42644f80c0 headroom = 47
 Interpreter Sp=0x7f42644ef238 SpLim=0x7f42644ef0c0 headroom = 47
 Interpreter Sp=0x7f42644e7238 SpLim=0x7f42644e70c0 headroom = 47
 Interpreter Sp=0x7f42644de238 SpLim=0x7f42644de0c0 headroom = 47
 Interpreter Sp=0x7f42644d6238 SpLim=0x7f42644d60c0 headroom = 47
 Interpreter Sp=0x7f42644ce238 SpLim=0x7f42644ce0c0 headroom = 47
 Interpreter Sp=0x7f42644c5238 SpLim=0x7f42644c50c0 headroom = 47
 Interpreter Sp=0x7f42644bd238 SpLim=0x7f42644bd0c0 headroom = 47
 Interpreter Sp=0x7f42644b4238 SpLim=0x7f42644b40c0 headroom = 47
 Interpreter Sp=0x7f42644ac238 SpLim=0x7f42644ac0c0 headroom = 47
 Interpreter Sp=0x7f42644a4238 SpLim=0x7f42644a40c0 headroom = 47
 Interpreter Sp=0x7f426449b238 SpLim=0x7f426449b0c0 headroom = 47
 Interpreter Sp=0x7f4264493238 SpLim=0x7f42644930c0 headroom = 47
 Interpreter Sp=0x7f426448a238 SpLim=0x7f426448a0c0 headroom = 47
 Interpreter Sp=0x7f4264482238 SpLim=0x7f42644820c0 headroom = 47
 Interpreter Sp=0x7f426447a238 SpLim=0x7f426447a0c0 headroom = 47
 Interpreter Sp=0x7f426454e238 SpLim=0x7f426454e0c0 headroom = 47
 Interpreter Sp=0x7f42641e8238 SpLim=0x7f42641e80c0 headroom = 47
 Interpreter Sp=0x7f426417c238 SpLim=0x7f426417c0c0 headroom = 47
 Interpreter Sp=0x7f4264174238 SpLim=0x7f42641740c0 headroom = 47
 Interpreter Sp=0x7f426416c238 SpLim=0x7f426416c0c0 headroom = 47
 Interpreter Sp=0x7f4264164238 SpLim=0x7f42641640c0 headroom = 47
 Interpreter Sp=0x7f426415c238 SpLim=0x7f426415c0c0 headroom = 47
 Interpreter Sp=0x7f4264154238 SpLim=0x7f42641540c0 headroom = 47
 Interpreter Sp=0x7f426414c238 SpLim=0x7f426414c0c0 headroom = 47
 Interpreter Sp=0x7f42643e0238 SpLim=0x7f42643e00c0 headroom = 47
 Interpreter Sp=0x7f42643d8238 SpLim=0x7f42643d80c0 headroom = 47
 Interpreter Sp=0x7f42643d0238 SpLim=0x7f42643d00c0 headroom = 47
 Interpreter Sp=0x7f42643c8238 SpLim=0x7f42643c80c0 headroom = 47
 Interpreter Sp=0x7f42643c0238 SpLim=0x7f42643c00c0 headroom = 47
 Interpreter Sp=0x7f42643b8238 SpLim=0x7f42643b80c0 headroom = 47
 Interpreter Sp=0x7f42643e0238 SpLim=0x7f42643e00c0 headroom = 47
 Interpreter Sp=0x7f4264154138 SpLim=0x7f42641540c0 headroom = 15
 Interpreter Sp=0x7f42641541d0 SpLim=0x7f42641540c0 headroom = 34
 Interpreter Sp=0x7f426415c230 SpLim=0x7f426415c0c0 headroom = 46
 Interpreter Sp=0x7f4264164130 SpLim=0x7f42641640c0 headroom = 14
 Interpreter Sp=0x7f42641641c8 SpLim=0x7f42641640c0 headroom = 33
 Interpreter Sp=0x7f426447a0e0 SpLim=0x7f426447a0c0 headroom = 4
 Interpreter Sp=0x7f426447a178 SpLim=0x7f426447a0c0 headroom = 23
 Interpreter Sp=0x7f426447a210 SpLim=0x7f426447a0c0 headroom = 42
 Interpreter Sp=0x7f4264482138 SpLim=0x7f42644820c0 headroom = 15
 Interpreter Sp=0x7f42644821d0 SpLim=0x7f42644820c0 headroom = 34
 Interpreter Sp=0x7f426448a228 SpLim=0x7f426448a0c0 headroom = 45
 Interpreter Sp=0x7f4264493238 SpLim=0x7f42644930c0 headroom = 47
 Interpreter Sp=0x7f426449b130 SpLim=0x7f426449b0c0 headroom = 14
 Interpreter Sp=0x7f426449b1c8 SpLim=0x7f426449b0c0 headroom = 33
 Interpreter Sp=0x7f42644ac0d0 SpLim=0x7f42644ac0c0 headroom = 2
 Interpreter Sp=0x7f42644ac168 SpLim=0x7f42644ac0c0 headroom = 21
 Interpreter Sp=0x7f42644ac200 SpLim=0x7f42644ac0c0 headroom = 40
 Interpreter Sp=0x7f42644b4230 SpLim=0x7f42644b40c0 headroom = 46
 Interpreter Sp=0x7f42644bd108 SpLim=0x7f42644bd0c0 headroom = 9
 Interpreter Sp=0x7f42644bd1a0 SpLim=0x7f42644bd0c0 headroom = 28
 Interpreter Sp=0x7f42644bd238 SpLim=0x7f42644bd0c0 headroom = 47
 Interpreter Sp=0x7f42644ce140 SpLim=0x7f42644ce0c0 headroom = 16
 Interpreter Sp=0x7f42644ce1d8 SpLim=0x7f42644ce0c0 headroom = 35
 Interpreter Sp=0x7f42644d6218 SpLim=0x7f42644d60c0 headroom = 43
 Interpreter Sp=0x7f42644de0e0 SpLim=0x7f42644de0c0 headroom = 4
 Interpreter Sp=0x7f42644de178 SpLim=0x7f42644de0c0 headroom = 23
 Interpreter Sp=0x7f42644de210 SpLim=0x7f42644de0c0 headroom = 42
 Interpreter Sp=0x7f42644e70c0 SpLim=0x7f42644e70c0 headroom = 0
 Interpreter Sp=0x7f42644e7158 SpLim=0x7f42644e70c0 headroom = 19
 Interpreter Sp=0x7f42644e71f0 SpLim=0x7f42644e70c0 headroom = 38
 Interpreter Sp=0x7f42644ef230 SpLim=0x7f42644ef0c0 headroom = 46
 Interpreter Sp=0x7f42644f8190 SpLim=0x7f42644f80c0 headroom = 26
 Interpreter Sp=0x7f42644f8228 SpLim=0x7f42644f80c0 headroom = 45
 Interpreter Sp=0x7f42641f00d8 SpLim=0x7f42641f00c0 headroom = 3
 Interpreter Sp=0x7f42641f0170 SpLim=0x7f42641f00c0 headroom = 22
 Interpreter Sp=0x7f42641f0208 SpLim=0x7f42641f00c0 headroom = 41
 Interpreter Sp=0x7f4257fb8210 SpLim=0x7f4257fb80c0 headroom = 42
 Interpreter Sp=0x7f4257fb80f0 SpLim=0x7f4257fb80c0 headroom = 6
 Interpreter Sp=0x7f4257fb8188 SpLim=0x7f4257fb80c0 headroom = 25
 Interpreter Sp=0x7f4257fb8220 SpLim=0x7f4257fb80c0 headroom = 44
 Interpreter Sp=0x7f4257fc00d0 SpLim=0x7f4257fc00c0 headroom = 2
 Interpreter Sp=0x7f4257fc0168 SpLim=0x7f4257fc00c0 headroom = 21
 Interpreter Sp=0x7f4257fc0200 SpLim=0x7f4257fc00c0 headroom = 40
 Interpreter Sp=0x7f4257fc80b0 SpLim=0x7f4257fc80c0 headroom = -2    <----
 NB
 Interpreter Sp=0x7f4257fc8148 SpLim=0x7f4257fc80c0 headroom = 17
 Interpreter Sp=0x7f4257fc81e0 SpLim=0x7f4257fc80c0 headroom = 36
 Interpreter Sp=0x7f4257fd0228 SpLim=0x7f4257fd00c0 headroom = 45
 Interpreter Sp=0x7f4257fe0228 SpLim=0x7f4257fe00c0 headroom = 45
 Interpreter Sp=0x7f4257fe8140 SpLim=0x7f4257fe80c0 headroom = 16
 Interpreter Sp=0x7f4257fe81d8 SpLim=0x7f4257fe80c0 headroom = 35
 Interpreter Sp=0x7f4257ff0120 SpLim=0x7f4257ff00c0 headroom = 12
 Interpreter Sp=0x7f4257ff01b8 SpLim=0x7f4257ff00c0 headroom = 31
 Interpreter Sp=0x7f4257ff8100 SpLim=0x7f4257ff80c0 headroom = 8
 Interpreter Sp=0x7f4257ff8198 SpLim=0x7f4257ff80c0 headroom = 27
 Interpreter Sp=0x7f4257ff8230 SpLim=0x7f4257ff80c0 headroom = 46
 Interpreter Sp=0x7f4264a060e0 SpLim=0x7f4264a060c0 headroom = 4
 Interpreter Sp=0x7f4264a06178 SpLim=0x7f4264a060c0 headroom = 23
 Interpreter Sp=0x7f4264a06210 SpLim=0x7f4264a060c0 headroom = 42
 Interpreter Sp=0x7f4264a0e0c0 SpLim=0x7f4264a0e0c0 headroom = 0
 Interpreter Sp=0x7f4264a0e158 SpLim=0x7f4264a0e0c0 headroom = 19
 Interpreter Sp=0x7f4264a0e1f0 SpLim=0x7f4264a0e0c0 headroom = 38
 Interpreter Sp=0x7f4264a16138 SpLim=0x7f4264a160c0 headroom = 15
 Interpreter Sp=0x7f4264a161d0 SpLim=0x7f4264a160c0 headroom = 34
 Interpreter Sp=0x7f4264a1e118 SpLim=0x7f4264a1e0c0 headroom = 11
 }}}

 So yes, we get into a situation in which we have negative headroom.
 Presumably if the ASSERT is off, we simply don't notice.  But it's clearly
 wrong.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9741
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