[GHC] #11395: The via-C code generation backend is incompatible with gcc 5.3.1 on m68k (ELF)

[GHC]

#11395: The via-C code generation backend is incompatible with gcc 5.3.1 on m68k
(ELF)
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        Reporter:  mkarcher                 |                Owner:
            Type:  bug                      |               Status:  new
        Priority:  normal                   |            Milestone:
       Component:  Compiler                 |              Version:  7.10.2
      Resolution:                           |             Keywords:
Operating System:  Linux                    |         Architecture:  m68k
 Type of failure:  GHC doesn't work at all  |            Test Case:
      Blocked By:                           |             Blocking:
 Related Tickets:                           |  Differential Rev(s):
       Wiki Page:                           |
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Comment (by Sergei Trofimovich <siarheit@…>):

 In [changeset:"c42cdb7f6dcfd519d9607ac9fa53f049b2922fb8/ghc" c42cdb7/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="c42cdb7f6dcfd519d9607ac9fa53f049b2922fb8"
 fix Float/Double unreg cross-compilation

 Looking at more failures on m68k (Trac #11395)
 I've noticed the arith001 and arith012 test failures.
 (--host=x86_64-linux --target=m68k-linux).

 The following example was enough to reproduce a problem:

     v :: Float
     v = 43
     main = print v

 m68k binaries printed '0.0' instead of '43.0'.

 The bug here is how we encode Floats and Double
 as Words with the same binary representation.

 Floats:
   Before the patch we just coerced Float to Int.
   That breaks when we cross-compile from
   64-bit LE to 32-bit BE.

   The patch fixes conversion by accounting for padding.
   when we extend 32-bit value to 64-bit value (LE and BE
   do it slightly differently).

 Doubles:
   Before the patch Doubles were coerced to a pair of Ints
   (not correct as x86_64 can hold Double in one Int) and
   then trucated this pair of Ints to pair of Word32.

   The patch fixes conversion by always decomposing in
   Word32 and accounting for host endianness (newly
   introduced hostBE)  and target endianness (wORDS_BIGENDIAN).

 I've tested this patch on Double and Float conversion on
     --host=x86_64-linux --target=m68k-linux
 crosscompiler. It fixes 10 tests related to printing Floats
 and Doubles.

 Thanks to Bertram Felgenhauer who poined out this probem.

 Signed-off-by: Sergei Trofimovich <siarheit at google.com>

 Test Plan: checked some examples manually, fixed 10 tests in test suite

 Reviewers: int-e, austin, bgamari

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D1990

 GHC Trac Issues: #11395
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11395#comment:24>
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