[GHC] #9480: Segfault in GHC API code using Shelly

[GHC]

#9480: Segfault in GHC API code using Shelly
-------------------------------------+-------------------------------------
              Reporter:  agibiansky  |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  GHC API     |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:  Linux       |     Architecture:  Unknown/Multiple
       Type of failure:  Runtime     |       Difficulty:  Unknown
  crash                              |       Blocked By:
             Test Case:              |  Related Tickets:  #8935
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
Changes (by rwbarton):

 * related:   => #8935


Comment:

 More `environ` nightmares, with the added twist of the GHCi linker. The
 problem arises here in `PrelIOUtils.o`:

 {{{
 00000000000002b0 <__hscore_environ>:
  2b0:   48 8b 05 00 00 00 00    mov    0x0(%rip),%rax        # 2b7
 <__hscore_environ+0x7>
                         2b3: R_X86_64_PC32      environ-0x4
  2b7:   c3                      retq
 }}}
 `-Dl` has the following to say about this: [edited slightly for
 readability]
 {{{
 Rel entry   2 is raw( 0x2b3 0x3a00000002 0xfffffffffffffffc)
 lookupSymbol: looking up environ
 initLinker: start
 initLinker: idempotent return
 lookupSymbol: symbol not found
 `environ' resolves to 0x7ffff7039fd8
 Reloc: P = 0x44f0e2f3   S = 0x7ffff7039fd8   A = 0xfffffffffffffffc
 }}}

 Now `environ` is too far away to use a PC-relative 32-bit reference, so
 the GHCi linker makes a jump island, but that's nonsense since `environ`
 isn't a function but rather a pointer to an array of C strings.

 But, also `0x7ffff7039fd8` isn't the ''right'' `environ` according to gdb:
 there is NULL there. What gdb thinks is `environ` (and my environment does
 actually appear there) is `0x7ffff7ffe140`... which is also too far away
 from the relocation site.

 I wonder how this all worked when you typed
 `System.Environment.getEnvironment` into GHCi 7.6?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9480#comment:1>
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