Re: [GHC] #16302: A non-function coerced to a function can cause a stg_ap_v_ret (was: A non-function coerced to a function can cause a stg_ap_pp_ret)

11 Feb 2019

      #16302: A non-function coerced to a function can cause a stg_ap_v_ret
-------------------------------------+-------------------------------------
        Reporter:  WheatWizard       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:  x86_64
                                     |  (amd64)
 Type of failure:  Runtime crash     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by WheatWizard:

Old description:
...
If you create an function by unsafe coercing a non-function you can get
some strange functions.  If you then take one of these function and apply
it something it crashes with a {{{stg_ap_pp_ret}}}.  Here is a pretty
minimal example.
{{{
import Unsafe.Coerce
main=(unsafeCoerce()::a->IO())1
}}}
You can reproduce it online here:
https://tio.run/##y0gszk7Nyfn/PzO3IL@oRCE0rzgxLVXPOT@1KDmVKzcxM89WoxQsBhHS0L...
Here is another one:
{{{
import Unsafe.Coerce
g=unsafeCoerce()::a->a
main=print$g(g)1
}}}
If you coerce functions this doesn't appear to happen.
For example:
{{{
import Unsafe.Coerce
main=(unsafeCoerce id::a->IO())1
}}}
is a fine program.  Sometimes this causes a segmentation fault
(particularly with higher airity functions):
{{{
import Unsafe.Coerce
main=(unsafeCoerce(+)::a->IO())1
}}}
but I've never gotten it to make a {{{stg_ap_pp_ret}}}.
New description:

 If you create an function by unsafe coercing a non-function you can get
 some strange functions.  If you then take one of these function and apply
 it something it crashes with a {{{stg_ap_v_ret}}}.  Here is a pretty
 minimal example.

 {{{
 import Unsafe.Coerce
 main=(unsafeCoerce()::a->IO())1
 }}}

 You can reproduce it online here:
 https://tio.run/##y0gszk7Nyfn/PzO3IL@oRCE0rzgxLVXPOT@1KDmVKzcxM89WoxQsBhHS0L...

 Here is another one:

 {{{
 import Unsafe.Coerce
 g=unsafeCoerce()::a->a
 main=print$g(g)1
 }}}

 If you coerce functions this doesn't appear to happen.

 For example:

 {{{
 import Unsafe.Coerce
 main=(unsafeCoerce id::a->IO())1
 }}}

 is a fine program.  Sometimes this causes a segmentation fault
 (particularly with higher airity functions):

 {{{
 import Unsafe.Coerce
 main=(unsafeCoerce(+)::a->IO())1
 }}}

 but I've never gotten it to make a {{{stg_ap_v_ret}}}.

--

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16302#comment:2
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