melf-1.2.0: examples/ForwardLabel.hs

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE RecursiveDo #-}

module ForwardLabel (forwardLabel) where

import Prelude as P

import Control.Monad.Fix
import Control.Monad.State
import Data.Word

import AsmAArch64

ok :: String
ok = "ok\n"

bad :: String
bad = "bad\n"

-- | syscalls
sysExit, sysWrite :: Word16
sysWrite = 64
sysExit = 93

forwardLabel :: MonadFix m => StateT CodeState m ()
forwardLabel = mdo

    label >>= exportSymbol "_start"

    lOk <- ascii ok
    lBad <- ascii bad

    mov x0 1

    adr x1 lOk
    mov x2 $ fromIntegral $ P.length ok

    b skipBad

    adr x1 lBad
    mov x2 $ fromIntegral $ P.length bad

    skipBad <- label

    mov x8 sysWrite
    svc 0

    mov x0 0
    mov x8 sysExit
    svc 0