[GHC] #13491: UNIQUE_BITS is not crosscompiler-friendly

28 Mar 2017

      #13491: UNIQUE_BITS is not crosscompiler-friendly
-------------------------------------+-------------------------------------
           Reporter:  slyfox         |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Things break when I try to build crosscompiler from 32-bit system to
 64-bit system. For example i386-linux -> powerpc64-linux:

 {{{
 $ ./configure --target=powerpc64-unknown-linux-gnu --with-system-libffi
 --with-libffi-includes=/usr/lib/libffi-3.2.1/include/
 $ make

 "inplace/bin/ghc-stage1" -static  -H32m -O
 -optc-I/usr/lib/libffi-3.2.1/include -Wall   -Iincludes -Iincludes/dist
 -Iincludes/dist-derivedconstants/header -Iincludes/dist-
 ghcconstants/header
 -Irts -Irts/dist/build -DCOMPILING_RTS -this-unit-id rts -dcmm-lint
 -i -irts -irts/dist/build -Irts/dist/build -irts/dist/build/./autogen
 -Irts/dist/build/./autogen           -O2    -Wno
 ncanonical-monad-instances  -c rts/StgStartup.cmm -o
 rts/dist/build/StgStartup.o
 /tmp/ghc19687_0/ghc_4.s: Assembler messages:

 /tmp/ghc19687_0/ghc_4.s:11:0: error:
      Error: unknown pseudo-op: `.l'
    |
 11 | .L�4:
    | ^

 }}}

 The problem here comes from definition of `UNIQUE_BITS`:
 {{{#!hs
 # cat compiler/Unique.h
 #include "../includes/MachDeps.h"

 #define UNIQUE_BITS (WORD_SIZE_IN_BITS - 8)
 }}}

 Here `WORD_SIZE_IN_BITS` is a target platform size (64) while `stage1`
 is still running on host platform (32).

 As a result uniques truncate down to zero:
 {{{#!hs
 compiler/basicTypes/Unique.hs:    tag  = ord c `shiftL` UNIQUE_BITS
 compiler/basicTypes/Unique.hs:        tag = chr (u `shiftR` UNIQUE_BITS)
 }}}

 As we operate on host '''Int'''s we could use the following:
 {{{#!hs
 #define UNIQUE_BITS sizeof(HsInt) * 8 -- C code

 #define UNIQUE_BITS (finiteBitSize (undefined :: Int) * 8) -- Haskell code
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13491
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler