[GHC] #11338: Unwind information is incorrect in region surrounding a safe foreign call

[GHC]

#11338: Unwind information is incorrect in region surrounding a safe foreign call
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.10.3
  (CodeGen)                          |
      Resolution:  invalid           |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Debugging         |  Unknown/Multiple
  information is incorrect           |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11337, #11353    |  Differential Rev(s):  Phab:D2743
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"3eb737ee3f900f256a7474b199a4ab40178a8cac/ghc" 3eb737e/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="3eb737ee3f900f256a7474b199a4ab40178a8cac"
 Generalize CmmUnwind and pass unwind information through NCG

 As discussed in D1532, Trac Trac #11337, and Trac Trac #11338, the stack
 unwinding information produced by GHC is currently quite approximate.
 Essentially we assume that register values do not change at all within a
 basic block. While this is somewhat true in normal Haskell code, blocks
 containing foreign calls often break this assumption. This results in
 unreliable call stacks, especially in the code containing foreign calls.
 This is worse than it sounds as unreliable unwinding information can at
 times result in segmentation faults.

 This patch set attempts to improve this situation by tracking unwinding
 information with finer granularity. By dispensing with the assumption of
 one unwinding table per block, we allow the compiler to accurately
 represent the areas surrounding foreign calls.

 Towards this end we generalize the representation of unwind information
 in the backend in three ways,

  * Multiple CmmUnwind nodes can occur per block

  * CmmUnwind nodes can now carry unwind information for multiple
    registers (while not strictly necessary; this makes emitting
    unwinding information a bit more convenient in the compiler)

  * The NCG backend is given an opportunity to modify the unwinding
    records since it may need to make adjustments due to, for instance,
    native calling convention requirements for foreign calls (see
    #11353).

 This sets the stage for resolving #11337 and #11338.

 Test Plan: Validate

 Reviewers: scpmw, simonmar, austin, erikd

 Subscribers: qnikst, thomie

 Differential Revision: https://phabricator.haskell.org/D2741
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11338#comment:6>
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