[GHC] #10969: Arm: Investigate Thumb2/Arm interworking

[GHC]

#10969: Arm: Investigate Thumb2/Arm interworking
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        Reporter:  erikd               |                Owner:
            Type:  bug                 |               Status:  new
        Priority:  normal              |            Milestone:
       Component:  Compiler (CodeGen)  |              Version:  7.11
      Resolution:                      |             Keywords:  arm, thumb
Operating System:  Unknown/Multiple    |         Architecture:  arm
 Type of failure:  None/Unknown        |            Test Case:
      Blocked By:                      |             Blocking:
 Related Tickets:  #10375              |  Differential Rev(s):
       Wiki Page:                      |
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Comment (by erikd):

 Before I wrote up this ticket I actually did some testing, building GHC
 with three changes on top of what became commit
 [changeset:"933adc0f31164cb651d11ecfcfe612ac429f714f/ghc" 933adc0f/ghc]:

 * Removed the `-marm` that was being passed to gcc.
 * In `compiler/llvmGen/LlvmCodeGen/Ppr.hs` set the target triple to
 `thumbv6-unknown-linux-gnueabihb` to force the Haskell via LLVM path to
 generate Thumb2 code.
 * Revert the change to `compiler/ghci/ByteCodeItbls.hs` so that it
 generates Thumb2 code.

 I also manually checked (using `objdump -d` on the object files) that both
 the via-gcc and the via-llvm paths were generating Thumb2 code.

 However, with the changes above the first stage2 execuable to run crashes
 immediately with an illegal instruction. Unfortunately I don't have time
 to work on this further right now as I would like to prioritize getting
 Arm64 working for the 8.0 release.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10969#comment:2>
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