[GHC] #15446: compiling files in ghci on MacOS eventually results in malformed mach-o: load commands size (32800) > 32768

[GHC]

#15446: compiling files in ghci on MacOS eventually results in malformed mach-o:
load commands size (32800) > 32768
--------------------------------------+-------------------------------
           Reporter:  George          |             Owner:  (none)
               Type:  bug             |            Status:  new
           Priority:  normal          |         Milestone:  8.8.1
          Component:  GHCi            |           Version:  8.4.3
           Keywords:                  |  Operating System:  MacOS X
       Architecture:  x86_64 (amd64)  |   Type of failure:  GHCi crash
          Test Case:                  |        Blocked By:
           Blocking:                  |   Related Tickets:
Differential Rev(s):                  |         Wiki Page:
--------------------------------------+-------------------------------
 compiling files in ghci on MacOS eventually results in a panic with error:

 {{{
 malformed mach-o: load commands size (32800) > 32768
 }}}

 I can reproduce this problem by repeatedly compiling (and loading) a file
 and then deleting the .o file. I understand that this an OS limitation but
 why does repeatedly doing the same thing results in this? i.e. why don't I
 get it on the first compile (and load). It seems that successive loads are
 being appended to something eventually resulting in the error.

 To duplicate:

 ghci -ignore-dot-ghci -fobject-code < ghci.sh >& ghci.out &

 If you look for the first "panic" in the .out file you'll see

 {{{
 Prelude Main> ghc: panic! (the 'impossible' happened)
   (GHC version 8.6.0.20180714 for x86_64-apple-darwin):
         Loading temp shared object failed:
 dlopen(/var/folders/9b/rh4y2gy92hgdb6ktv4df1jv00000gn/T/ghc55569_0/libghc_2084.dylib,
 5): no suitable image found.  Did find:
 /var/folders/9b/rh4y2gy92hgdb6ktv4df1jv00000gn/T/ghc55569_0/libghc_2084.dylib:
 malformed mach-o: load commands size (32800) > 32768
 /var/folders/9b/rh4y2gy92hgdb6ktv4df1jv00000gn/T/ghc55569_0/libghc_2084.dylib:
 stat() failed with errno=25
 }}}

 The critical part being
 {{{
 malformed mach-o: load commands size (32800) > 32768
 }}}

 My understanding from https://stackoverflow.com/questions/44902695/too-
 many-commands-dyld-message-malformed-mach-o-load-commands-size is that
 this has to do with sizeofcmds but if I understand the output of otool 0l
 this is only 512 so I don't understand what is causing the errror.

 {{{
  otool -l c.o|head
 c.o:
 Mach header
       magic cputype cpusubtype  caps    filetype ncmds sizeofcmds
 flags
  0xfeedfacf 16777223          3  0x00           1     4        512
 0x00002000
 }}}

 This is irritating but perhaps the priority should be low rather than
 normal.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15446>
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