• Ömer Sinan Ağacan's avatar
    Fix slop zeroing for AP_STACK eager blackholes in debug build · 66c17293
    Ömer Sinan Ağacan authored
    As #15571 reports, eager blackholing breaks sanity checks as we can't
    zero the payload when eagerly blackholing (because we'll be using the
    payload after blackholing), but by the time we blackhole a previously
    eagerly blackholed object (in `threadPaused()`) we don't have the
    correct size information for the object (because the object's type
    becomes BLACKHOLE when we eagerly blackhole it) so can't properly zero
    the slop.
    
    This problem can be solved for AP_STACK eager blackholing (which unlike
    eager blackholing in general, is not optional) by zeroing the payload
    after entering the stack. This patch implements this idea.
    
    Fixes #15571.
    
    Test Plan:
    Previously concprog001 when compiled and run with sanity checks
    
        ghc-stage2 Mult.hs -debug -rtsopts
        ./Mult +RTS -DS
    
    was failing with
    
        Mult: internal error: checkClosure: stack frame
            (GHC version 8.7.20180821 for x86_64_unknown_linux)
            Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
    
    thic patch fixes this panic. The test still panics, but it runs for a while
    before panicking (instead of directly panicking as before), and the new problem
    seems unrelated:
    
        Mult: internal error: ASSERTION FAILED: file rts/sm/Sanity.c, line 296
            (GHC version 8.7.20180919 for x86_64_unknown_linux)
            Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
    
    The new problem will be fixed in another diff.
    
    I also tried slow validate (which requires D5164): this does not introduce any
    new failures.
    
    Reviewers: simonmar, bgamari, erikd
    
    Reviewed By: simonmar
    
    Subscribers: rwbarton, carter
    
    GHC Trac Issues: #15571
    
    Differential Revision: https://phabricator.haskell.org/D5165
    66c17293
ClosureMacros.h 21.3 KB