[GHC] #15092: Optionally bounds-check primops

[GHC]

#15092: Optionally bounds-check primops
-------------------------------------+-------------------------------------
        Reporter:  dfeuer            |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.2.2
  (CodeGen)                          |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by osa1):

 I also frequently need this when debugging memory corruptions (e.g.
 #15038).

 > The biggest challenge: SomeException, Typeable, Show, String, CallStack,
 etc.

 Why is this a challenge? I don't see the relation between with these type
 classes and array operations.

 > I think a hard crash is completely appropriate. Bound violations are
 programming errors thus there is no way to safely recover from them,
 anyway.

 Agreed, but I think there's another approach: raising an exception. We
 already raise exceptions for runtime errors like non-exhaustive pattern
 mathing. We could do the same. We already have the type defined:
 http://hackage.haskell.org/package/base-4.11.1.0/docs/Control-
 Exception.html#t:ArrayException

 For my use case, even just a "out of bounds access!" message would do it
 so I don't feel strongly either way. Note that currently GHC (in DWARF
 version) already prints the C stack trace on panic:

 {{{
 Main: internal error: evacuate(static): strange closure type 16583
 Stack trace:
                   0x4b4dfb    set_initial_registers (rts/Libdw.c:288.0)
             0x7f37ccfb3558    dwfl_thread_getframes (/usr/lib/x86_64
 -linux-gnu/libdw-0.165.so)
             0x7f37ccfb2faf    (null) (/usr/lib/x86_64-linux-
 gnu/libdw-0.165.so)
             0x7f37ccfb32d7    dwfl_getthreads (/usr/lib/x86_64-linux-
 gnu/libdw-0.165.so)
             0x7f37ccfb38e0    dwfl_getthread_frames (/usr/lib/x86_64
 -linux-gnu/libdw-0.165.so)
                   0x4b538d    libdwGetBacktrace (rts/Libdw.c:259.0)
                   0x49ce1c    rtsFatalInternalErrorFn
 (rts/RtsMessages.c:172.0)
                   0x49cfad    barf (rts/RtsMessages.c:48.0)
                   0x4a162e    evacuate
 (includes/rts/storage/Block.h:175.0)
                   0x4b765b    scavenge_loop (rts/sm/Scav.c:1830.0)
                   0x4a0532    GarbageCollect (rts/sm/GC.c:1423.0)
                   0x49bb87    scheduleDoGC (rts/Schedule.c:1814.0)
                   0x49c8c4    scheduleWaitThread (rts/Schedule.c:558.0)
                   0x49d450    rts_evalLazyIO (rts/RtsAPI.c:531.0)
                   0x49d75b    hs_main (rts/RtsMain.c:73.0)
                   0x40d6aa    (null) (/home/omer/haskell/corrupted-memory-
 example/Main)
             0x7f37ccbd7830    __libc_start_main (../csu/libc-
 start.c:325.0)
                   0x4042f9    _start (/home/omer/haskell/corrupted-memory-
 example/Main)

     (GHC version 8.4.2 for x86_64_unknown_linux)
     Please report this as a GHC bug:
 http://www.haskell.org/ghc/reportabug
 [1]    3391 abort (core dumped)  ./Main
 }}}

 So we get some information for free already.

 > My concerns about the "hard crash" approach: the error messages may not
 be as informative as one might wish

 I'm curious what kind of error messages you'd like to get?

 I think the main problem is for "out of line" array operations like
 `copyArray#` we'll need one more variant of RTS, so longer GHC boot times,
 more code to distribute etc. Not sure how to avoid this.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15092#comment:3>
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