[GHC] #2972: ppc ghci segfaults at startup

[GHC]

#2972: ppc ghci segfaults at startup
------------------------+---------------------------------------------------
    Reporter:  cemeyer  |       Owner:  pcapriotti
        Type:  bug      |      Status:  patch     
    Priority:  normal   |   Milestone:  7.6.1     
   Component:  GHCi     |     Version:  7.5       
    Keywords:           |          Os:  Linux     
Architecture:  powerpc  |     Failure:  GHCi crash
  Difficulty:  Unknown  |    Testcase:            
   Blockedby:           |    Blocking:            
     Related:           |  
------------------------+---------------------------------------------------

Comment(by erikd@…):

 commit 3e6c9308777caf83122baef504028d619d3dd588
 {{{
 Author: Erik de Castro Lopo <erikd at mega-nerd.com>
 Date:   Tue Jul 31 05:53:49 2012 +1000

     Fix GHCi segfault during startup on linux-powerpc (#2972).

     Slightly modified version of a patch from Ben Collins
 <bcollins at ubuntu.com>
     who did the final debugging that showed the segfault was being caused
 the
     memory protection mechanism.

     Due to the requirement of "jump islands" to handle 24 bit relative
 jump
     offsets, GHCi on PowerPC did not use mmap to load object files like
 the
     other architectures. Instead, it allocated memory using malloc and
 fread
     to load the object code. However there is a quirk in the GNU libc
 malloc
     implementation. For memory regions over certain size (dynamic and
     configurable), malloc will use mmap to obtain the required memory
 instead
     of sbrk and malloc's call to mmap sets the memory readable and
 writable,
     but not executable. That means when GHCi loads code into a memory
 region
     that was mmapped instead of malloc-ed and tries to execute it we get a
     segfault.

     This solution drops the malloc/fread object loading in favour of using
     mmap and then puts the jump island for each object code module at the
     end of the mmaped region for that object.

     This patch may also be a solution on other ELF based powerpc systems
     but does not work on darwin-powerpc.

  rts/Linker.c |   37 +++++++++++++++++++++++++++++++++----
  1 files changed, 33 insertions(+), 4 deletions(-)
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2972#comment:32>
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