[GHC] #8935: Obscure linker bug leads to crash in GHCi

[GHC]

#8935: Obscure linker bug leads to crash in GHCi
-------------------------------------+------------------------------------
        Reporter:  simonmar          |            Owner:  simonmar
            Type:  bug               |           Status:  infoneeded
        Priority:  high              |        Milestone:  7.8.3
       Component:  Runtime System    |          Version:  7.8.1-rc2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  GHCi crash        |       Difficulty:  Rocket Science
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
-------------------------------------+------------------------------------

Comment (by simonmar):

 `libgmp` is not symbolic on my system either.

 Symbol information and relocs for the program:

 {{{
 $ objdump --syms --dynamic-syms --reloc --dynamic-reloc ./a.out | grep
 envir
 0000000000000000 l    df *ABS*  0000000000000000              check-
 environ.c
 0000000000601060  w    O .bss   0000000000000008
 environ@@GLIBC_2.2.5
 0000000000601060 g     O .bss   0000000000000008
 __environ@@GLIBC_2.2.5
 0000000000601060  w   DO .bss   0000000000000008  GLIBC_2.2.5 _environ
 0000000000601060  w   DO .bss   0000000000000008  GLIBC_2.2.5 environ
 0000000000601060 g    DO .bss   0000000000000008  GLIBC_2.2.5 __environ
 0000000000601060 R_X86_64_COPY     __environ
 }}}

 Note there are 3 symbols at the same location (`environ`, `_environ`, and
 `__environ`).  The first two are weak, the third is global.  The third is
 also a copy reloc, which means its contents is copied to this location
 when the program starts up.

 Symbol information and relocs for libc:

 {{{
 $ objdump --syms --dynamic-syms --reloc --dynamic-reloc /lib/x86_64-linux-
 gnu/libc-2.17.so | grep envir
 00000000003c44e8  w   DO .bss   0000000000000008  GLIBC_2.2.5 _environ
 00000000003c44e8  w   DO .bss   0000000000000008  GLIBC_2.2.5 environ
 00000000003c44e8 g    DO .bss   0000000000000008  GLIBC_2.2.5 __environ
 00000000003c0de0 R_X86_64_GLOB_DAT  _environ
 00000000003c0ea8 R_X86_64_GLOB_DAT  __environ
 }}}

 Again we have 3 symbols at the same location, all 8 bytes long.

 There are no mentions of any `environ` symbol in `libgmp`'s symbol table
 or relocations.

 `LD_DEBUG=all` shows a normal lookup like this:

 {{{
      23419:     symbol=environ;  lookup in file=./a.out [0]
      23419:     binding file ./a.out [0] to ./a.out [0]: normal symbol
 `environ'
 }}}

 but the lookup in `libgmp` looks like this:

 {{{
      23419:     symbol=environ;  lookup in file=/usr/lib/x86_64-linux-
 gnu/libgmp.so [0]
      23419:     symbol=environ;  lookup in file=/lib/x86_64-linux-
 gnu/libc.so.6 [0]
      23419:     binding file /usr/lib/x86_64-linux-gnu/libgmp.so [0] to
 /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `environ'
 }}}

 I still have no idea why the lookup in `libgmp` is behaving differently
 from the others.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8935#comment:17>
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