squash haskell: PR suggestions

Signed-off-by: Corey Lewis <[email protected]>

spec/haskell/src/SEL4/Object/FPU/AARCH64.hs

@@ -18,6 +18,7 @@ import {-# SOURCE #-} SEL4.Object.TCB(asUser, threadGet)
 
 import Data.Bits
 import Data.Maybe
+import Data.Traversable(for)
 
 saveFpuState :: PPtr TCB -> Kernel ()
 saveFpuState tcbPtr = do
@@ -33,10 +34,10 @@ switchLocalFpuOwner :: Maybe (PPtr TCB) -> Kernel ()
 switchLocalFpuOwner newOwner = do
     doMachineOp enableFpu
     curFpuOwner <- gets (armKSCurFPUOwner . ksArchState)
-    when (isJust curFpuOwner) (saveFpuState (fromJust curFpuOwner))
-    if isJust newOwner
-      then loadFpuState (fromJust newOwner)
-      else doMachineOp disableFpu
+    for curFpuOwner saveFpuState
+    case newOwner of
+        Nothing -> doMachineOp disableFpu
+        Just tcbPtr -> loadFpuState tcbPtr
     modifyArchState (\s -> s { armKSCurFPUOwner = newOwner })
 
 fpuRelease :: PPtr TCB -> Kernel ()

spec/haskell/src/SEL4/Object/TCB/AARCH64.hs

@@ -58,6 +58,8 @@ postSetFlags :: PPtr TCB -> TcbFlags -> Kernel ()
 postSetFlags t flags =
     when (tcbFlagToWord (ArchFlag FpuDisabled) .&. flags /= 0) (fpuRelease t)
 
+-- Save and clear FPU state before setting the domain of a TCB, to ensure that
+-- we do not later write to cross-domain state.
 prepareSetDomain :: PPtr TCB -> Domain -> Kernel ()
 prepareSetDomain t newDom = do
     curDom <- curDomain