[GHC] #15338: ghc-pkg misbehaves after possible miscompilation on m68k and sh4

[GHC]

#15338: ghc-pkg misbehaves after possible miscompilation on m68k and sh4
-------------------------------------+-------------------------------------
        Reporter:  glaubitz          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:  m68k
 Type of failure:  Incorrect result  |            Test Case:
  at runtime                         |
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4959
       Wiki Page:                    |
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Comment (by Sergei Trofimovich <slyfox@…>):

 In [changeset:"8ec48990fee9e245bb2fe40dc6f65b61b8612157/ghc"
 8ec48990/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="8ec48990fee9e245bb2fe40dc6f65b61b8612157"
 driver: skip -Bsymbolic on unregisterised targets (Trac #15338)

 Trac #15338 is yet another example where -Bsymbolic breaks
 semantics of a C program: global variable duplication happens
 and unsafePerformIO creates two stdout copies.

 When -Bsymbolic is not used both C compiler and linker agree
 on how global variables are handled. In case of sh4 it consists
 on a few assertions:

 1. global variable is exported from shared library
 2. code is referred to this variable via GOT-like mechanism to allow
    interposition
 3. global variable is present .bss section on an executable
    (as an R_*_COPY relocation: symbol contents is copied at executable
    startup time)
 4. and symbol in executable interposes symbol in shared library.

 This way both code in shared library and code in executable refer
 to a copy of global variable in .bss section of an executable.

 Unfortunately -Bsymbolic option breaks assumption [2.] and generates
 direct references to the symbol. This causes mismatch between
 values seen from executable and values seen from shared library code.

 This change disables '-Bsymbolic' for unregisterised targets.

 Signed-off-by: Sergei Trofimovich <slyfox at gentoo.org>

 Test Plan: test 'ghc-pkg --version | cat' to emit data

 Reviewers: simonmar, bgamari, jrtc27

 Reviewed By: jrtc27

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #15338

 Differential Revision: https://phabricator.haskell.org/D4959
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15338#comment:10>
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