{-# LANGUAGE GADTs #-}
{-# LANGUAGE MultiWayIf #-}

{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}

-----------------------------------------------------------------------------
--
-- Debugging data
--
-- Association of debug data on the Cmm level, with methods to encode it in
-- event log format for later inclusion in profiling event logs.
--
-----------------------------------------------------------------------------

module GHC.Cmm.DebugBlock (

  DebugBlock(..),
  cmmDebugGen,
  cmmDebugLabels,
  cmmDebugLink,
  debugToMap,

  -- * Unwinding information
  UnwindTable, UnwindPoint(..),
  UnwindExpr(..), toUnwindExpr
  ) where

import GHC.Prelude

import GHC.Platform
import GHC.Cmm.BlockId
import GHC.Cmm.CLabel
import GHC.Cmm
import GHC.Cmm.Utils
import GHC.Core
import GHC.Data.FastString ( nilFS, mkFastString )
import GHC.Unit.Module
import GHC.Utils.Outputable
import GHC.Cmm.Ppr.Expr ( pprExpr )
import GHC.Types.SrcLoc
import GHC.Utils.Misc      ( seqList )

import GHC.Cmm.Dataflow.Block
import GHC.Cmm.Dataflow.Collections
import GHC.Cmm.Dataflow.Graph
import GHC.Cmm.Dataflow.Label

import Data.Maybe
import Data.List     ( minimumBy, nubBy )
import Data.Ord      ( comparing )
import qualified Data.Map as Map
import Data.Either   ( partitionEithers )

-- | Debug information about a block of code. Ticks scope over nested
-- blocks.
data DebugBlock =
  DebugBlock
  { DebugBlock -> Label
dblProcedure  :: !Label        -- ^ Entry label of containing proc
  , DebugBlock -> Label
dblLabel      :: !Label        -- ^ Hoopl label
  , DebugBlock -> CLabel
dblCLabel     :: !CLabel       -- ^ Output label
  , DebugBlock -> Bool
dblHasInfoTbl :: !Bool         -- ^ Has an info table?
  , DebugBlock -> Maybe DebugBlock
dblParent     :: !(Maybe DebugBlock)
    -- ^ The parent of this proc. See Note [Splitting DebugBlocks]
  , DebugBlock -> [Tickish ()]
dblTicks      :: ![CmmTickish] -- ^ Ticks defined in this block
  , DebugBlock -> Maybe (Tickish ())
dblSourceTick :: !(Maybe CmmTickish) -- ^ Best source tick covering block
  , DebugBlock -> Maybe Int
dblPosition   :: !(Maybe Int)  -- ^ Output position relative to
                                   -- other blocks. @Nothing@ means
                                   -- the block was optimized out
  , DebugBlock -> [UnwindPoint]
dblUnwind     :: [UnwindPoint]
  , DebugBlock -> [DebugBlock]
dblBlocks     :: ![DebugBlock] -- ^ Nested blocks
  }

instance Outputable DebugBlock where
  ppr :: DebugBlock -> SDoc
ppr DebugBlock
blk = (if | DebugBlock -> Label
dblProcedure DebugBlock
blk Label -> Label -> Bool
forall a. Eq a => a -> a -> Bool
External instance of the constraint type Eq Label
== DebugBlock -> Label
dblLabel DebugBlock
blk
                -> String -> SDoc
text String
"proc"
                | DebugBlock -> Bool
dblHasInfoTbl DebugBlock
blk
                -> String -> SDoc
text String
"pp-blk"
                | Bool
otherwise
                -> String -> SDoc
text String
"blk") SDoc -> SDoc -> SDoc
<+>
            Label -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type Outputable Label
ppr (DebugBlock -> Label
dblLabel DebugBlock
blk) SDoc -> SDoc -> SDoc
<+> SDoc -> SDoc
parens (CLabel -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type Outputable CLabel
ppr (DebugBlock -> CLabel
dblCLabel DebugBlock
blk)) SDoc -> SDoc -> SDoc
<+>
            (SDoc -> (Tickish () -> SDoc) -> Maybe (Tickish ()) -> SDoc
forall b a. b -> (a -> b) -> Maybe a -> b
maybe SDoc
empty Tickish () -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type forall id. Outputable id => Outputable (Tickish id)
External instance of the constraint type Outputable ()
ppr (DebugBlock -> Maybe (Tickish ())
dblSourceTick DebugBlock
blk)) SDoc -> SDoc -> SDoc
<+>
            (SDoc -> (Int -> SDoc) -> Maybe Int -> SDoc
forall b a. b -> (a -> b) -> Maybe a -> b
maybe (String -> SDoc
text String
"removed") ((String -> SDoc
text String
"pos " SDoc -> SDoc -> SDoc
<>) (SDoc -> SDoc) -> (Int -> SDoc) -> Int -> SDoc
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Int -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type Outputable Int
ppr)
                   (DebugBlock -> Maybe Int
dblPosition DebugBlock
blk)) SDoc -> SDoc -> SDoc
<+>
            ([UnwindPoint] -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type forall a. Outputable a => Outputable [a]
Instance of class: Outputable of the constraint type Outputable UnwindPoint
ppr (DebugBlock -> [UnwindPoint]
dblUnwind DebugBlock
blk)) SDoc -> SDoc -> SDoc
$+$
            (if [DebugBlock] -> Bool
forall (t :: * -> *) a. Foldable t => t a -> Bool
External instance of the constraint type Foldable []
null (DebugBlock -> [DebugBlock]
dblBlocks DebugBlock
blk) then SDoc
empty else Int -> SDoc -> SDoc
nest Int
4 ([DebugBlock] -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type forall a. Outputable a => Outputable [a]
Instance of class: Outputable of the constraint type Outputable DebugBlock
ppr (DebugBlock -> [DebugBlock]
dblBlocks DebugBlock
blk)))

-- | Intermediate data structure holding debug-relevant context information
-- about a block.
type BlockContext = (CmmBlock, RawCmmDecl)

-- | Extract debug data from a group of procedures. We will prefer
-- source notes that come from the given module (presumably the module
-- that we are currently compiling).
cmmDebugGen :: ModLocation -> RawCmmGroup -> [DebugBlock]
cmmDebugGen :: ModLocation -> RawCmmGroup -> [DebugBlock]
cmmDebugGen ModLocation
modLoc RawCmmGroup
decls = (CmmTickScope -> DebugBlock) -> [CmmTickScope] -> [DebugBlock]
forall a b. (a -> b) -> [a] -> [b]
map (Maybe (Tickish ()) -> CmmTickScope -> DebugBlock
blocksForScope Maybe (Tickish ())
forall a. Maybe a
Nothing) [CmmTickScope]
topScopes
  where
      blockCtxs :: Map.Map CmmTickScope [BlockContext]
      blockCtxs :: Map CmmTickScope [BlockContext]
blockCtxs = RawCmmGroup -> Map CmmTickScope [BlockContext]
blockContexts RawCmmGroup
decls

      -- Analyse tick scope structure: Each one is either a top-level
      -- tick scope, or the child of another.
      ([CmmTickScope]
topScopes, [(CmmTickScope, CmmTickScope)]
childScopes)
        = [Either CmmTickScope (CmmTickScope, CmmTickScope)]
-> ([CmmTickScope], [(CmmTickScope, CmmTickScope)])
forall a b. [Either a b] -> ([a], [b])
partitionEithers ([Either CmmTickScope (CmmTickScope, CmmTickScope)]
 -> ([CmmTickScope], [(CmmTickScope, CmmTickScope)]))
-> [Either CmmTickScope (CmmTickScope, CmmTickScope)]
-> ([CmmTickScope], [(CmmTickScope, CmmTickScope)])
forall a b. (a -> b) -> a -> b
$ (CmmTickScope -> Either CmmTickScope (CmmTickScope, CmmTickScope))
-> [CmmTickScope]
-> [Either CmmTickScope (CmmTickScope, CmmTickScope)]
forall a b. (a -> b) -> [a] -> [b]
map (\CmmTickScope
a -> CmmTickScope
-> CmmTickScope -> Either CmmTickScope (CmmTickScope, CmmTickScope)
forall {t}. t -> CmmTickScope -> Either t (CmmTickScope, t)
findP CmmTickScope
a CmmTickScope
a) ([CmmTickScope]
 -> [Either CmmTickScope (CmmTickScope, CmmTickScope)])
-> [CmmTickScope]
-> [Either CmmTickScope (CmmTickScope, CmmTickScope)]
forall a b. (a -> b) -> a -> b
$ Map CmmTickScope [BlockContext] -> [CmmTickScope]
forall k a. Map k a -> [k]
Map.keys Map CmmTickScope [BlockContext]
blockCtxs
      findP :: t -> CmmTickScope -> Either t (CmmTickScope, t)
findP t
tsc CmmTickScope
GlobalScope = t -> Either t (CmmTickScope, t)
forall a b. a -> Either a b
Left t
tsc -- top scope
      findP t
tsc CmmTickScope
scp | CmmTickScope
scp' CmmTickScope -> Map CmmTickScope [BlockContext] -> Bool
forall k a. Ord k => k -> Map k a -> Bool
External instance of the constraint type Ord CmmTickScope
`Map.member` Map CmmTickScope [BlockContext]
blockCtxs = (CmmTickScope, t) -> Either t (CmmTickScope, t)
forall a b. b -> Either a b
Right (CmmTickScope
scp', t
tsc)
                    | Bool
otherwise                   = t -> CmmTickScope -> Either t (CmmTickScope, t)
findP t
tsc CmmTickScope
scp'
        where -- Note that we only following the left parent of
              -- combined scopes. This loses us ticks, which we will
              -- recover by copying ticks below.
              scp' :: CmmTickScope
scp' | SubScope Unique
_ CmmTickScope
scp' <- CmmTickScope
scp      = CmmTickScope
scp'
                   | CombinedScope CmmTickScope
scp' CmmTickScope
_ <- CmmTickScope
scp = CmmTickScope
scp'
                   | Bool
otherwise                   = String -> CmmTickScope
forall a. String -> a
panic String
"findP impossible"

      scopeMap :: Map CmmTickScope [CmmTickScope]
scopeMap = ((CmmTickScope, CmmTickScope)
 -> Map CmmTickScope [CmmTickScope]
 -> Map CmmTickScope [CmmTickScope])
-> Map CmmTickScope [CmmTickScope]
-> [(CmmTickScope, CmmTickScope)]
-> Map CmmTickScope [CmmTickScope]
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
External instance of the constraint type Foldable []
foldr ((CmmTickScope
 -> CmmTickScope
 -> Map CmmTickScope [CmmTickScope]
 -> Map CmmTickScope [CmmTickScope])
-> (CmmTickScope, CmmTickScope)
-> Map CmmTickScope [CmmTickScope]
-> Map CmmTickScope [CmmTickScope]
forall a b c. (a -> b -> c) -> (a, b) -> c
uncurry CmmTickScope
-> CmmTickScope
-> Map CmmTickScope [CmmTickScope]
-> Map CmmTickScope [CmmTickScope]
forall k a. Ord k => k -> a -> Map k [a] -> Map k [a]
External instance of the constraint type Ord CmmTickScope
insertMulti) Map CmmTickScope [CmmTickScope]
forall k a. Map k a
Map.empty [(CmmTickScope, CmmTickScope)]
childScopes

      -- This allows us to recover ticks that we lost by flattening
      -- the graph. Basically, if the parent is A but the child is
      -- CBA, we know that there is no BA, because it would have taken
      -- priority - but there might be a B scope, with ticks that
      -- would not be associated with our child anymore. Note however
      -- that there might be other childs (DB), which we have to
      -- filter out.
      --
      -- We expect this to be called rarely, which is why we are not
      -- trying too hard to be efficient here. In many cases we won't
      -- have to construct blockCtxsU in the first place.
      ticksToCopy :: CmmTickScope -> [CmmTickish]
      ticksToCopy :: CmmTickScope -> [Tickish ()]
ticksToCopy (CombinedScope CmmTickScope
scp CmmTickScope
s) = CmmTickScope -> [Tickish ()]
go CmmTickScope
s
        where go :: CmmTickScope -> [Tickish ()]
go CmmTickScope
s | CmmTickScope
scp CmmTickScope -> CmmTickScope -> Bool
`isTickSubScope` CmmTickScope
s   = [] -- done
                   | SubScope Unique
_ CmmTickScope
s' <- CmmTickScope
s       = [Tickish ()]
ticks [Tickish ()] -> [Tickish ()] -> [Tickish ()]
forall a. [a] -> [a] -> [a]
++ CmmTickScope -> [Tickish ()]
go CmmTickScope
s'
                   | CombinedScope CmmTickScope
s1 CmmTickScope
s2 <- CmmTickScope
s = [Tickish ()]
ticks [Tickish ()] -> [Tickish ()] -> [Tickish ()]
forall a. [a] -> [a] -> [a]
++ CmmTickScope -> [Tickish ()]
go CmmTickScope
s1 [Tickish ()] -> [Tickish ()] -> [Tickish ()]
forall a. [a] -> [a] -> [a]
++ CmmTickScope -> [Tickish ()]
go CmmTickScope
s2
                   | Bool
otherwise                = String -> [Tickish ()]
forall a. String -> a
panic String
"ticksToCopy impossible"
                where ticks :: [Tickish ()]
ticks = [BlockContext] -> [Tickish ()]
forall {b}. [(Block CmmNode C C, b)] -> [Tickish ()]
bCtxsTicks ([BlockContext] -> [Tickish ()]) -> [BlockContext] -> [Tickish ()]
forall a b. (a -> b) -> a -> b
$ [BlockContext] -> Maybe [BlockContext] -> [BlockContext]
forall a. a -> Maybe a -> a
fromMaybe [] (Maybe [BlockContext] -> [BlockContext])
-> Maybe [BlockContext] -> [BlockContext]
forall a b. (a -> b) -> a -> b
$ CmmTickScope
-> Map CmmTickScope [BlockContext] -> Maybe [BlockContext]
forall k a. Ord k => k -> Map k a -> Maybe a
External instance of the constraint type Ord CmmTickScope
Map.lookup CmmTickScope
s Map CmmTickScope [BlockContext]
blockCtxs
      ticksToCopy CmmTickScope
_ = []
      bCtxsTicks :: [(Block CmmNode C C, b)] -> [Tickish ()]
bCtxsTicks = ((Block CmmNode C C, b) -> [Tickish ()])
-> [(Block CmmNode C C, b)] -> [Tickish ()]
forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
External instance of the constraint type Foldable []
concatMap (Block CmmNode C C -> [Tickish ()]
blockTicks (Block CmmNode C C -> [Tickish ()])
-> ((Block CmmNode C C, b) -> Block CmmNode C C)
-> (Block CmmNode C C, b)
-> [Tickish ()]
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (Block CmmNode C C, b) -> Block CmmNode C C
forall a b. (a, b) -> a
fst)

      -- Finding the "best" source tick is somewhat arbitrary -- we
      -- select the first source span, while preferring source ticks
      -- from the same source file.  Furthermore, dumps take priority
      -- (if we generated one, we probably want debug information to
      -- refer to it).
      bestSrcTick :: [Tickish ()] -> Tickish ()
bestSrcTick = (Tickish () -> Tickish () -> Ordering)
-> [Tickish ()] -> Tickish ()
forall (t :: * -> *) a.
Foldable t =>
(a -> a -> Ordering) -> t a -> a
External instance of the constraint type Foldable []
minimumBy ((Tickish () -> Int) -> Tickish () -> Tickish () -> Ordering
forall a b. Ord a => (b -> a) -> b -> b -> Ordering
External instance of the constraint type Ord Int
comparing Tickish () -> Int
rangeRating)
      rangeRating :: Tickish () -> Int
rangeRating (SourceNote RealSrcSpan
span String
_)
        | RealSrcSpan -> FastString
srcSpanFile RealSrcSpan
span FastString -> FastString -> Bool
forall a. Eq a => a -> a -> Bool
External instance of the constraint type Eq FastString
== FastString
thisFile = Int
1
        | Bool
otherwise                    = Int
2 :: Int
      rangeRating Tickish ()
note                 = String -> SDoc -> Int
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"rangeRating" (Tickish () -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type forall id. Outputable id => Outputable (Tickish id)
External instance of the constraint type Outputable ()
ppr Tickish ()
note)
      thisFile :: FastString
thisFile = FastString -> (String -> FastString) -> Maybe String -> FastString
forall b a. b -> (a -> b) -> Maybe a -> b
maybe FastString
nilFS String -> FastString
mkFastString (Maybe String -> FastString) -> Maybe String -> FastString
forall a b. (a -> b) -> a -> b
$ ModLocation -> Maybe String
ml_hs_file ModLocation
modLoc

      -- Returns block tree for this scope as well as all nested
      -- scopes. Note that if there are multiple blocks in the (exact)
      -- same scope we elect one as the "branch" node and add the rest
      -- as children.
      blocksForScope :: Maybe CmmTickish -> CmmTickScope -> DebugBlock
      blocksForScope :: Maybe (Tickish ()) -> CmmTickScope -> DebugBlock
blocksForScope Maybe (Tickish ())
cstick CmmTickScope
scope = Bool -> BlockContext -> DebugBlock
mkBlock Bool
True ([BlockContext] -> BlockContext
forall a. [a] -> a
head [BlockContext]
bctxs)
        where bctxs :: [BlockContext]
bctxs = Maybe [BlockContext] -> [BlockContext]
forall a. HasCallStack => Maybe a -> a
fromJust (Maybe [BlockContext] -> [BlockContext])
-> Maybe [BlockContext] -> [BlockContext]
forall a b. (a -> b) -> a -> b
$ CmmTickScope
-> Map CmmTickScope [BlockContext] -> Maybe [BlockContext]
forall k a. Ord k => k -> Map k a -> Maybe a
External instance of the constraint type Ord CmmTickScope
Map.lookup CmmTickScope
scope Map CmmTickScope [BlockContext]
blockCtxs
              nested :: [CmmTickScope]
nested = [CmmTickScope] -> Maybe [CmmTickScope] -> [CmmTickScope]
forall a. a -> Maybe a -> a
fromMaybe [] (Maybe [CmmTickScope] -> [CmmTickScope])
-> Maybe [CmmTickScope] -> [CmmTickScope]
forall a b. (a -> b) -> a -> b
$ CmmTickScope
-> Map CmmTickScope [CmmTickScope] -> Maybe [CmmTickScope]
forall k a. Ord k => k -> Map k a -> Maybe a
External instance of the constraint type Ord CmmTickScope
Map.lookup CmmTickScope
scope Map CmmTickScope [CmmTickScope]
scopeMap
              childs :: [DebugBlock]
childs = (BlockContext -> DebugBlock) -> [BlockContext] -> [DebugBlock]
forall a b. (a -> b) -> [a] -> [b]
map (Bool -> BlockContext -> DebugBlock
mkBlock Bool
False) ([BlockContext] -> [BlockContext]
forall a. [a] -> [a]
tail [BlockContext]
bctxs) [DebugBlock] -> [DebugBlock] -> [DebugBlock]
forall a. [a] -> [a] -> [a]
++
                       (CmmTickScope -> DebugBlock) -> [CmmTickScope] -> [DebugBlock]
forall a b. (a -> b) -> [a] -> [b]
map (Maybe (Tickish ()) -> CmmTickScope -> DebugBlock
blocksForScope Maybe (Tickish ())
stick) [CmmTickScope]
nested

              mkBlock :: Bool -> BlockContext -> DebugBlock
              mkBlock :: Bool -> BlockContext -> DebugBlock
mkBlock Bool
top (Block CmmNode C C
block, RawCmmDecl
prc)
                = DebugBlock :: Label
-> Label
-> CLabel
-> Bool
-> Maybe DebugBlock
-> [Tickish ()]
-> Maybe (Tickish ())
-> Maybe Int
-> [UnwindPoint]
-> [DebugBlock]
-> DebugBlock
DebugBlock { dblProcedure :: Label
dblProcedure    = GenCmmGraph CmmNode -> Label
forall (n :: Extensibility -> Extensibility -> *).
GenCmmGraph n -> Label
g_entry GenCmmGraph CmmNode
graph
                             , dblLabel :: Label
dblLabel        = Label
label
                             , dblCLabel :: CLabel
dblCLabel       = case Maybe RawCmmStatics
info of
                                 Just (CmmStaticsRaw CLabel
infoLbl [CmmStatic]
_) -> CLabel
infoLbl
                                 Maybe RawCmmStatics
Nothing
                                   | GenCmmGraph CmmNode -> Label
forall (n :: Extensibility -> Extensibility -> *).
GenCmmGraph n -> Label
g_entry GenCmmGraph CmmNode
graph Label -> Label -> Bool
forall a. Eq a => a -> a -> Bool
External instance of the constraint type Eq Label
== Label
label -> CLabel
entryLbl
                                   | Bool
otherwise              -> Label -> CLabel
blockLbl Label
label
                             , dblHasInfoTbl :: Bool
dblHasInfoTbl   = Maybe RawCmmStatics -> Bool
forall a. Maybe a -> Bool
isJust Maybe RawCmmStatics
info
                             , dblParent :: Maybe DebugBlock
dblParent       = Maybe DebugBlock
forall a. Maybe a
Nothing
                             , dblTicks :: [Tickish ()]
dblTicks        = [Tickish ()]
ticks
                             , dblPosition :: Maybe Int
dblPosition     = Maybe Int
forall a. Maybe a
Nothing -- see cmmDebugLink
                             , dblSourceTick :: Maybe (Tickish ())
dblSourceTick   = Maybe (Tickish ())
stick
                             , dblBlocks :: [DebugBlock]
dblBlocks       = [DebugBlock]
blocks
                             , dblUnwind :: [UnwindPoint]
dblUnwind       = []
                             }
                where (CmmProc LabelMap RawCmmStatics
infos CLabel
entryLbl [GlobalReg]
_ GenCmmGraph CmmNode
graph) = RawCmmDecl
prc
                      label :: Label
label = Block CmmNode C C -> Label
forall (thing :: Extensibility -> Extensibility -> *)
       (x :: Extensibility).
NonLocal thing =>
thing C x -> Label
External instance of the constraint type forall (n :: Extensibility -> Extensibility -> *).
NonLocal n =>
NonLocal (Block n)
External instance of the constraint type NonLocal CmmNode
entryLabel Block CmmNode C C
block
                      info :: Maybe RawCmmStatics
info = KeyOf LabelMap -> LabelMap RawCmmStatics -> Maybe RawCmmStatics
forall (map :: * -> *) a.
IsMap map =>
KeyOf map -> map a -> Maybe a
External instance of the constraint type IsMap LabelMap
mapLookup KeyOf LabelMap
Label
label LabelMap RawCmmStatics
infos
                      blocks :: [DebugBlock]
blocks | Bool
top       = [DebugBlock] -> [DebugBlock] -> [DebugBlock]
forall a b. [a] -> b -> b
seqList [DebugBlock]
childs [DebugBlock]
childs
                             | Bool
otherwise = []

              -- A source tick scopes over all nested blocks. However
              -- their source ticks might take priority.
              isSourceTick :: Tickish id -> Bool
isSourceTick SourceNote {} = Bool
True
              isSourceTick Tickish id
_             = Bool
False
              -- Collect ticks from all blocks inside the tick scope.
              -- We attempt to filter out duplicates while we're at it.
              ticks :: [Tickish ()]
ticks = (Tickish () -> Tickish () -> Bool) -> [Tickish ()] -> [Tickish ()]
forall a. (a -> a -> Bool) -> [a] -> [a]
nubBy ((Tickish () -> Tickish () -> Bool)
-> Tickish () -> Tickish () -> Bool
forall a b c. (a -> b -> c) -> b -> a -> c
flip Tickish () -> Tickish () -> Bool
forall b. Eq b => Tickish b -> Tickish b -> Bool
External instance of the constraint type Eq ()
tickishContains) ([Tickish ()] -> [Tickish ()]) -> [Tickish ()] -> [Tickish ()]
forall a b. (a -> b) -> a -> b
$
                      [BlockContext] -> [Tickish ()]
forall {b}. [(Block CmmNode C C, b)] -> [Tickish ()]
bCtxsTicks [BlockContext]
bctxs [Tickish ()] -> [Tickish ()] -> [Tickish ()]
forall a. [a] -> [a] -> [a]
++ CmmTickScope -> [Tickish ()]
ticksToCopy CmmTickScope
scope
              stick :: Maybe (Tickish ())
stick = case (Tickish () -> Bool) -> [Tickish ()] -> [Tickish ()]
forall a. (a -> Bool) -> [a] -> [a]
filter Tickish () -> Bool
forall {id}. Tickish id -> Bool
isSourceTick [Tickish ()]
ticks of
                []     -> Maybe (Tickish ())
cstick
                [Tickish ()]
sticks -> Tickish () -> Maybe (Tickish ())
forall a. a -> Maybe a
Just (Tickish () -> Maybe (Tickish ()))
-> Tickish () -> Maybe (Tickish ())
forall a b. (a -> b) -> a -> b
$! [Tickish ()] -> Tickish ()
bestSrcTick ([Tickish ()]
sticks [Tickish ()] -> [Tickish ()] -> [Tickish ()]
forall a. [a] -> [a] -> [a]
++ Maybe (Tickish ()) -> [Tickish ()]
forall a. Maybe a -> [a]
maybeToList Maybe (Tickish ())
cstick)

-- | Build a map of blocks sorted by their tick scopes
--
-- This involves a pre-order traversal, as we want blocks in rough
-- control flow order (so ticks have a chance to be sorted in the
-- right order).
blockContexts :: RawCmmGroup -> Map.Map CmmTickScope [BlockContext]
blockContexts :: RawCmmGroup -> Map CmmTickScope [BlockContext]
blockContexts RawCmmGroup
decls = ([BlockContext] -> [BlockContext])
-> Map CmmTickScope [BlockContext]
-> Map CmmTickScope [BlockContext]
forall a b k. (a -> b) -> Map k a -> Map k b
Map.map [BlockContext] -> [BlockContext]
forall a. [a] -> [a]
reverse (Map CmmTickScope [BlockContext]
 -> Map CmmTickScope [BlockContext])
-> Map CmmTickScope [BlockContext]
-> Map CmmTickScope [BlockContext]
forall a b. (a -> b) -> a -> b
$ (RawCmmDecl
 -> Map CmmTickScope [BlockContext]
 -> Map CmmTickScope [BlockContext])
-> Map CmmTickScope [BlockContext]
-> RawCmmGroup
-> Map CmmTickScope [BlockContext]
forall (t :: * -> *) a b.
Foldable t =>
(a -> b -> b) -> b -> t a -> b
External instance of the constraint type Foldable []
foldr RawCmmDecl
-> Map CmmTickScope [BlockContext]
-> Map CmmTickScope [BlockContext]
walkProc Map CmmTickScope [BlockContext]
forall k a. Map k a
Map.empty RawCmmGroup
decls
  where walkProc :: RawCmmDecl
                 -> Map.Map CmmTickScope [BlockContext]
                 -> Map.Map CmmTickScope [BlockContext]
        walkProc :: RawCmmDecl
-> Map CmmTickScope [BlockContext]
-> Map CmmTickScope [BlockContext]
walkProc CmmData{}                 Map CmmTickScope [BlockContext]
m = Map CmmTickScope [BlockContext]
m
        walkProc prc :: RawCmmDecl
prc@(CmmProc LabelMap RawCmmStatics
_ CLabel
_ [GlobalReg]
_ GenCmmGraph CmmNode
graph) Map CmmTickScope [BlockContext]
m
          | LabelMap (Block CmmNode C C) -> Bool
forall (map :: * -> *) a. IsMap map => map a -> Bool
External instance of the constraint type IsMap LabelMap
mapNull LabelMap (Block CmmNode C C)
blocks = Map CmmTickScope [BlockContext]
m
          | Bool
otherwise      = (LabelSet, Map CmmTickScope [BlockContext])
-> Map CmmTickScope [BlockContext]
forall a b. (a, b) -> b
snd ((LabelSet, Map CmmTickScope [BlockContext])
 -> Map CmmTickScope [BlockContext])
-> (LabelSet, Map CmmTickScope [BlockContext])
-> Map CmmTickScope [BlockContext]
forall a b. (a -> b) -> a -> b
$ RawCmmDecl
-> [Block CmmNode C C]
-> (LabelSet, Map CmmTickScope [BlockContext])
-> (LabelSet, Map CmmTickScope [BlockContext])
walkBlock RawCmmDecl
prc [Block CmmNode C C]
entry (LabelSet
emptyLbls, Map CmmTickScope [BlockContext]
m)
          where blocks :: LabelMap (Block CmmNode C C)
blocks = GenCmmGraph CmmNode -> LabelMap (Block CmmNode C C)
toBlockMap GenCmmGraph CmmNode
graph
                entry :: [Block CmmNode C C]
entry  = [KeyOf LabelMap -> LabelMap (Block CmmNode C C) -> Block CmmNode C C
forall {a}. KeyOf LabelMap -> LabelMap a -> a
mapFind (GenCmmGraph CmmNode -> Label
forall (n :: Extensibility -> Extensibility -> *).
GenCmmGraph n -> Label
g_entry GenCmmGraph CmmNode
graph) LabelMap (Block CmmNode C C)
blocks]
                emptyLbls :: LabelSet
emptyLbls = LabelSet
forall set. IsSet set => set
External instance of the constraint type IsSet LabelSet
setEmpty :: LabelSet

        walkBlock :: RawCmmDecl -> [Block CmmNode C C]
                  -> (LabelSet, Map.Map CmmTickScope [BlockContext])
                  -> (LabelSet, Map.Map CmmTickScope [BlockContext])
        walkBlock :: RawCmmDecl
-> [Block CmmNode C C]
-> (LabelSet, Map CmmTickScope [BlockContext])
-> (LabelSet, Map CmmTickScope [BlockContext])
walkBlock RawCmmDecl
_   []             (LabelSet, Map CmmTickScope [BlockContext])
c            = (LabelSet, Map CmmTickScope [BlockContext])
c
        walkBlock RawCmmDecl
prc (Block CmmNode C C
block:[Block CmmNode C C]
blocks) (LabelSet
visited, Map CmmTickScope [BlockContext]
m)
          | ElemOf LabelSet
Label
lbl ElemOf LabelSet -> LabelSet -> Bool
forall set. IsSet set => ElemOf set -> set -> Bool
External instance of the constraint type IsSet LabelSet
`setMember` LabelSet
visited
          = RawCmmDecl
-> [Block CmmNode C C]
-> (LabelSet, Map CmmTickScope [BlockContext])
-> (LabelSet, Map CmmTickScope [BlockContext])
walkBlock RawCmmDecl
prc [Block CmmNode C C]
blocks (LabelSet
visited, Map CmmTickScope [BlockContext]
m)
          | Bool
otherwise
          = RawCmmDecl
-> [Block CmmNode C C]
-> (LabelSet, Map CmmTickScope [BlockContext])
-> (LabelSet, Map CmmTickScope [BlockContext])
walkBlock RawCmmDecl
prc [Block CmmNode C C]
blocks ((LabelSet, Map CmmTickScope [BlockContext])
 -> (LabelSet, Map CmmTickScope [BlockContext]))
-> (LabelSet, Map CmmTickScope [BlockContext])
-> (LabelSet, Map CmmTickScope [BlockContext])
forall a b. (a -> b) -> a -> b
$
            RawCmmDecl
-> [Block CmmNode C C]
-> (LabelSet, Map CmmTickScope [BlockContext])
-> (LabelSet, Map CmmTickScope [BlockContext])
walkBlock RawCmmDecl
prc [Block CmmNode C C]
succs
              (ElemOf LabelSet
Label
lbl ElemOf LabelSet -> LabelSet -> LabelSet
forall set. IsSet set => ElemOf set -> set -> set
External instance of the constraint type IsSet LabelSet
`setInsert` LabelSet
visited,
               CmmTickScope
-> BlockContext
-> Map CmmTickScope [BlockContext]
-> Map CmmTickScope [BlockContext]
forall k a. Ord k => k -> a -> Map k [a] -> Map k [a]
External instance of the constraint type Ord CmmTickScope
insertMulti CmmTickScope
scope (Block CmmNode C C
block, RawCmmDecl
prc) Map CmmTickScope [BlockContext]
m)
          where CmmEntry Label
lbl CmmTickScope
scope = Block CmmNode C C -> CmmNode C O
forall (n :: Extensibility -> Extensibility -> *)
       (x :: Extensibility).
Block n C x -> n C O
firstNode Block CmmNode C C
block
                (CmmProc LabelMap RawCmmStatics
_ CLabel
_ [GlobalReg]
_ GenCmmGraph CmmNode
graph) = RawCmmDecl
prc
                succs :: [Block CmmNode C C]
succs = (Label -> Block CmmNode C C) -> [Label] -> [Block CmmNode C C]
forall a b. (a -> b) -> [a] -> [b]
map ((Label -> LabelMap (Block CmmNode C C) -> Block CmmNode C C)
-> LabelMap (Block CmmNode C C) -> Label -> Block CmmNode C C
forall a b c. (a -> b -> c) -> b -> a -> c
flip Label -> LabelMap (Block CmmNode C C) -> Block CmmNode C C
forall {a}. KeyOf LabelMap -> LabelMap a -> a
mapFind (GenCmmGraph CmmNode -> LabelMap (Block CmmNode C C)
toBlockMap GenCmmGraph CmmNode
graph))
                            (CmmNode O C -> [Label]
forall (thing :: Extensibility -> Extensibility -> *)
       (e :: Extensibility).
NonLocal thing =>
thing e C -> [Label]
External instance of the constraint type NonLocal CmmNode
successors (Block CmmNode C C -> CmmNode O C
forall (n :: Extensibility -> Extensibility -> *)
       (x :: Extensibility).
Block n x C -> n O C
lastNode Block CmmNode C C
block))
        mapFind :: KeyOf LabelMap -> LabelMap a -> a
mapFind = a -> KeyOf LabelMap -> LabelMap a -> a
forall (map :: * -> *) a. IsMap map => a -> KeyOf map -> map a -> a
External instance of the constraint type IsMap LabelMap
mapFindWithDefault (String -> a
forall a. HasCallStack => String -> a
error String
"contextTree: block not found!")

insertMulti :: Ord k => k -> a -> Map.Map k [a] -> Map.Map k [a]
insertMulti :: k -> a -> Map k [a] -> Map k [a]
insertMulti k
k a
v = ([a] -> [a] -> [a]) -> k -> [a] -> Map k [a] -> Map k [a]
forall k a. Ord k => (a -> a -> a) -> k -> a -> Map k a -> Map k a
Evidence bound by a type signature of the constraint type Ord k
Map.insertWith (([a] -> [a]) -> [a] -> [a] -> [a]
forall a b. a -> b -> a
const (a
va -> [a] -> [a]
forall a. a -> [a] -> [a]
:)) k
k [a
v]

cmmDebugLabels :: (i -> Bool) -> GenCmmGroup d g (ListGraph i) -> [Label]
cmmDebugLabels :: (i -> Bool) -> GenCmmGroup d g (ListGraph i) -> [Label]
cmmDebugLabels i -> Bool
isMeta GenCmmGroup d g (ListGraph i)
nats = [Label] -> [Label] -> [Label]
forall a b. [a] -> b -> b
seqList [Label]
lbls [Label]
lbls
  where -- Find order in which procedures will be generated by the
        -- back-end (that actually matters for DWARF generation).
        --
        -- Note that we might encounter blocks that are missing or only
        -- consist of meta instructions -- we will declare them missing,
        -- which will skip debug data generation without messing up the
        -- block hierarchy.
        lbls :: [Label]
lbls = (GenBasicBlock i -> Label) -> [GenBasicBlock i] -> [Label]
forall a b. (a -> b) -> [a] -> [b]
map GenBasicBlock i -> Label
forall i. GenBasicBlock i -> Label
blockId ([GenBasicBlock i] -> [Label]) -> [GenBasicBlock i] -> [Label]
forall a b. (a -> b) -> a -> b
$ (GenBasicBlock i -> Bool) -> [GenBasicBlock i] -> [GenBasicBlock i]
forall a. (a -> Bool) -> [a] -> [a]
filter (Bool -> Bool
not (Bool -> Bool)
-> (GenBasicBlock i -> Bool) -> GenBasicBlock i -> Bool
forall b c a. (b -> c) -> (a -> b) -> a -> c
. GenBasicBlock i -> Bool
allMeta) ([GenBasicBlock i] -> [GenBasicBlock i])
-> [GenBasicBlock i] -> [GenBasicBlock i]
forall a b. (a -> b) -> a -> b
$ (GenCmmDecl d g (ListGraph i) -> [GenBasicBlock i])
-> GenCmmGroup d g (ListGraph i) -> [GenBasicBlock i]
forall (t :: * -> *) a b. Foldable t => (a -> [b]) -> t a -> [b]
External instance of the constraint type Foldable []
concatMap GenCmmDecl d g (ListGraph i) -> [GenBasicBlock i]
forall {d} {h} {i}.
GenCmmDecl d h (ListGraph i) -> [GenBasicBlock i]
getBlocks GenCmmGroup d g (ListGraph i)
nats
        getBlocks :: GenCmmDecl d h (ListGraph i) -> [GenBasicBlock i]
getBlocks (CmmProc h
_ CLabel
_ [GlobalReg]
_ (ListGraph [GenBasicBlock i]
bs)) = [GenBasicBlock i]
bs
        getBlocks GenCmmDecl d h (ListGraph i)
_other                         = []
        allMeta :: GenBasicBlock i -> Bool
allMeta (BasicBlock Label
_ [i]
instrs) = (i -> Bool) -> [i] -> Bool
forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
External instance of the constraint type Foldable []
all i -> Bool
isMeta [i]
instrs

-- | Sets position and unwind table fields in the debug block tree according to
-- native generated code.
cmmDebugLink :: [Label] -> LabelMap [UnwindPoint]
             -> [DebugBlock] -> [DebugBlock]
cmmDebugLink :: [Label] -> LabelMap [UnwindPoint] -> [DebugBlock] -> [DebugBlock]
cmmDebugLink [Label]
labels LabelMap [UnwindPoint]
unwindPts [DebugBlock]
blocks = (DebugBlock -> DebugBlock) -> [DebugBlock] -> [DebugBlock]
forall a b. (a -> b) -> [a] -> [b]
map DebugBlock -> DebugBlock
link [DebugBlock]
blocks
  where blockPos :: LabelMap Int
        blockPos :: LabelMap Int
blockPos = [(KeyOf LabelMap, Int)] -> LabelMap Int
forall (map :: * -> *) a. IsMap map => [(KeyOf map, a)] -> map a
External instance of the constraint type IsMap LabelMap
mapFromList ([(KeyOf LabelMap, Int)] -> LabelMap Int)
-> [(KeyOf LabelMap, Int)] -> LabelMap Int
forall a b. (a -> b) -> a -> b
$ ([Label] -> [Int] -> [(Label, Int)])
-> [Int] -> [Label] -> [(Label, Int)]
forall a b c. (a -> b -> c) -> b -> a -> c
flip [Label] -> [Int] -> [(Label, Int)]
forall a b. [a] -> [b] -> [(a, b)]
zip [Int
0..] [Label]
labels
        link :: DebugBlock -> DebugBlock
link DebugBlock
block = DebugBlock
block { dblPosition :: Maybe Int
dblPosition = KeyOf LabelMap -> LabelMap Int -> Maybe Int
forall (map :: * -> *) a.
IsMap map =>
KeyOf map -> map a -> Maybe a
External instance of the constraint type IsMap LabelMap
mapLookup (DebugBlock -> Label
dblLabel DebugBlock
block) LabelMap Int
blockPos
                           , dblBlocks :: [DebugBlock]
dblBlocks   = (DebugBlock -> DebugBlock) -> [DebugBlock] -> [DebugBlock]
forall a b. (a -> b) -> [a] -> [b]
map DebugBlock -> DebugBlock
link (DebugBlock -> [DebugBlock]
dblBlocks DebugBlock
block)
                           , dblUnwind :: [UnwindPoint]
dblUnwind   = [UnwindPoint] -> Maybe [UnwindPoint] -> [UnwindPoint]
forall a. a -> Maybe a -> a
fromMaybe [UnwindPoint]
forall a. Monoid a => a
External instance of the constraint type forall a. Monoid [a]
mempty
                                         (Maybe [UnwindPoint] -> [UnwindPoint])
-> Maybe [UnwindPoint] -> [UnwindPoint]
forall a b. (a -> b) -> a -> b
$ KeyOf LabelMap -> LabelMap [UnwindPoint] -> Maybe [UnwindPoint]
forall (map :: * -> *) a.
IsMap map =>
KeyOf map -> map a -> Maybe a
External instance of the constraint type IsMap LabelMap
mapLookup (DebugBlock -> Label
dblLabel DebugBlock
block) LabelMap [UnwindPoint]
unwindPts
                           }

-- | Converts debug blocks into a label map for easier lookups
debugToMap :: [DebugBlock] -> LabelMap DebugBlock
debugToMap :: [DebugBlock] -> LabelMap DebugBlock
debugToMap = [LabelMap DebugBlock] -> LabelMap DebugBlock
forall (map :: * -> *) a. IsMap map => [map a] -> map a
External instance of the constraint type IsMap LabelMap
mapUnions ([LabelMap DebugBlock] -> LabelMap DebugBlock)
-> ([DebugBlock] -> [LabelMap DebugBlock])
-> [DebugBlock]
-> LabelMap DebugBlock
forall b c a. (b -> c) -> (a -> b) -> a -> c
. (DebugBlock -> LabelMap DebugBlock)
-> [DebugBlock] -> [LabelMap DebugBlock]
forall a b. (a -> b) -> [a] -> [b]
map DebugBlock -> LabelMap DebugBlock
forall {map :: * -> *}.
(IsMap map, KeyOf map ~ Label) =>
DebugBlock -> map DebugBlock
External instance of the constraint type IsMap LabelMap
go
   where go :: DebugBlock -> map DebugBlock
go DebugBlock
b = KeyOf map -> DebugBlock -> map DebugBlock -> map DebugBlock
forall (map :: * -> *) a.
IsMap map =>
KeyOf map -> a -> map a -> map a
Evidence bound by a type signature of the constraint type IsMap map
mapInsert (DebugBlock -> Label
dblLabel DebugBlock
b) DebugBlock
b (map DebugBlock -> map DebugBlock)
-> map DebugBlock -> map DebugBlock
forall a b. (a -> b) -> a -> b
$ [map DebugBlock] -> map DebugBlock
forall (map :: * -> *) a. IsMap map => [map a] -> map a
Evidence bound by a type signature of the constraint type IsMap map
mapUnions ([map DebugBlock] -> map DebugBlock)
-> [map DebugBlock] -> map DebugBlock
forall a b. (a -> b) -> a -> b
$ (DebugBlock -> map DebugBlock) -> [DebugBlock] -> [map DebugBlock]
forall a b. (a -> b) -> [a] -> [b]
map DebugBlock -> map DebugBlock
go (DebugBlock -> [DebugBlock]
dblBlocks DebugBlock
b)

{-
Note [What is this unwinding business?]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Unwinding tables are a variety of debugging information used by debugging tools
to reconstruct the execution history of a program at runtime. These tables
consist of sets of "instructions", one set for every instruction in the program,
which describe how to reconstruct the state of the machine at the point where
the current procedure was called. For instance, consider the following annotated
pseudo-code,

  a_fun:
    add rsp, 8            -- unwind: rsp = rsp - 8
    mov rax, 1            -- unwind: rax = unknown
    call another_block
    sub rsp, 8            -- unwind: rsp = rsp

We see that attached to each instruction there is an "unwind" annotation, which
provides a relationship between each updated register and its value at the
time of entry to a_fun. This is the sort of information that allows gdb to give
you a stack backtrace given the execution state of your program. This
unwinding information is captured in various ways by various debug information
formats; in the case of DWARF (the only format supported by GHC) it is known as
Call Frame Information (CFI) and can be found in the .debug.frames section of
your object files.

Currently we only bother to produce unwinding information for registers which
are necessary to reconstruct flow-of-execution. On x86_64 this includes $rbp
(which is the STG stack pointer) and $rsp (the C stack pointer).

Let's consider how GHC would annotate a C-- program with unwinding information
with a typical C-- procedure as would come from the STG-to-Cmm code generator,

  entry()
     { c2fe:
           v :: P64 = R2;
           if ((Sp + 8) - 32 < SpLim) (likely: False) goto c2ff; else goto c2fg;
       c2ff:
           R2 = v :: P64;
           R1 = test_closure;
           call (stg_gc_fun)(R2, R1) args: 8, res: 0, upd: 8;
       c2fg:
           I64[Sp - 8] = c2dD;
           R1 = v :: P64;
           Sp = Sp - 8;          // Sp updated here
           if (R1 & 7 != 0) goto c2dD; else goto c2dE;
       c2dE:
           call (I64[R1])(R1) returns to c2dD, args: 8, res: 8, upd: 8;
       c2dD:
           w :: P64 = R1;
           Hp = Hp + 48;
           if (Hp > HpLim) (likely: False) goto c2fj; else goto c2fi;
       ...
  },

Let's consider how this procedure will be decorated with unwind information
(largely by GHC.Cmm.LayoutStack). Naturally, when we enter the procedure `entry` the
value of Sp is no different from what it was at its call site. Therefore we will
add an `unwind` statement saying this at the beginning of its unwind-annotated
code,

  entry()
     { c2fe:
           unwind Sp = Just Sp + 0;
           v :: P64 = R2;
           if ((Sp + 8) - 32 < SpLim) (likely: False) goto c2ff; else goto c2fg;

After c2fe we may pass to either c2ff or c2fg; let's first consider the
former. In this case there is nothing in particular that we need to do other
than reiterate what we already know about Sp,

       c2ff:
           unwind Sp = Just Sp + 0;
           R2 = v :: P64;
           R1 = test_closure;
           call (stg_gc_fun)(R2, R1) args: 8, res: 0, upd: 8;

In contrast, c2fg updates Sp midway through its body. To ensure that unwinding
can happen correctly after this point we must include an unwind statement there,
in addition to the usual beginning-of-block statement,

       c2fg:
           unwind Sp = Just Sp + 0;
           I64[Sp - 8] = c2dD;
           R1 = v :: P64;
           Sp = Sp - 8;
           unwind Sp = Just Sp + 8;
           if (R1 & 7 != 0) goto c2dD; else goto c2dE;

The remaining blocks are simple,

       c2dE:
           unwind Sp = Just Sp + 8;
           call (I64[R1])(R1) returns to c2dD, args: 8, res: 8, upd: 8;
       c2dD:
           unwind Sp = Just Sp + 8;
           w :: P64 = R1;
           Hp = Hp + 48;
           if (Hp > HpLim) (likely: False) goto c2fj; else goto c2fi;
       ...
  },


The flow of unwinding information through the compiler is a bit convoluted:

 * C-- begins life in StgToCmm without any unwind information. This is because we
   haven't actually done any register assignment or stack layout yet, so there
   is no need for unwind information.

 * GHC.Cmm.LayoutStack figures out how to layout each procedure's stack, and produces
   appropriate unwinding nodes for each adjustment of the STG Sp register.

 * The unwind nodes are carried through the sinking pass. Currently this is
   guaranteed not to invalidate unwind information since it won't touch stores
   to Sp, but this will need revisiting if CmmSink gets smarter in the future.

 * Eventually we make it to the native code generator backend which can then
   preserve the unwind nodes in its machine-specific instructions. In so doing
   the backend can also modify or add unwinding information; this is necessary,
   for instance, in the case of x86-64, where adjustment of $rsp may be
   necessary during calls to native foreign code due to the native calling
   convention.

 * The NCG then retrieves the final unwinding table for each block from the
   backend with extractUnwindPoints.

 * This unwind information is converted to DebugBlocks by Debug.cmmDebugGen

 * These DebugBlocks are then converted to, e.g., DWARF unwinding tables
   (by the Dwarf module) and emitted in the final object.

See also:
  Note [Unwinding information in the NCG] in AsmCodeGen,
  Note [Unwind pseudo-instruction in Cmm],
  Note [Debugging DWARF unwinding info].


Note [Debugging DWARF unwinding info]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

For debugging generated unwinding info I've found it most useful to dump the
disassembled binary with objdump -D and dump the debug info with
readelf --debug-dump=frames-interp.

You should get something like this:

  0000000000000010 <stg_catch_frame_info>:
    10:   48 83 c5 18             add    $0x18,%rbp
    14:   ff 65 00                jmpq   *0x0(%rbp)

and:

  Contents of the .debug_frame section:

  00000000 0000000000000014 ffffffff CIE "" cf=1 df=-8 ra=16
     LOC           CFA      rbp   rsp   ra
  0000000000000000 rbp+0    v+0   s     c+0

  00000018 0000000000000024 00000000 FDE cie=00000000 pc=000000000000000f..0000000000000017
     LOC           CFA      rbp   rsp   ra
  000000000000000f rbp+0    v+0   s     c+0
  000000000000000f rbp+24   v+0   s     c+0

To read it http://www.dwarfstd.org/doc/dwarf-2.0.0.pdf has a nice example in
Appendix 5 (page 101 of the pdf) and more details in the relevant section.

The key thing to keep in mind is that the value at LOC is the value from
*before* the instruction at LOC executes. In other words it answers the
question: if my $rip is at LOC, how do I get the relevant values given the
values obtained through unwinding so far.

If the readelf --debug-dump=frames-interp output looks wrong, it may also be
useful to look at readelf --debug-dump=frames, which is closer to the
information that GHC generated.

It's also useful to dump the relevant Cmm with -ddump-cmm -ddump-opt-cmm
-ddump-cmm-proc -ddump-cmm-verbose. Note [Unwind pseudo-instruction in Cmm]
explains how to interpret it.

Inside gdb there are a couple useful commands for inspecting frames.
For example:

  gdb> info frame <num>

It shows the values of registers obtained through unwinding.

Another useful thing to try when debugging the DWARF unwinding is to enable
extra debugging output in GDB:

  gdb> set debug frame 1

This makes GDB produce a trace of its internal workings. Having gone this far,
it's just a tiny step to run GDB in GDB. Make sure you install debugging
symbols for gdb if you obtain it through a package manager.

Keep in mind that the current release of GDB has an instruction pointer handling
heuristic that works well for C-like languages, but doesn't always work for
Haskell. See Note [Info Offset] in Dwarf.Types for more details.

Note [Unwind pseudo-instruction in Cmm]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

One of the possible CmmNodes is a CmmUnwind pseudo-instruction. It doesn't
generate any assembly, but controls what DWARF unwinding information gets
generated.

It's important to understand what ranges of code the unwind pseudo-instruction
refers to.
For a sequence of CmmNodes like:

  A // starts at addr X and ends at addr Y-1
  unwind Sp = Just Sp + 16;
  B // starts at addr Y and ends at addr Z

the unwind statement reflects the state after A has executed, but before B
has executed. If you consult the Note [Debugging DWARF unwinding info], the
LOC this information will end up in is Y.
-}

-- | A label associated with an 'UnwindTable'
data UnwindPoint = UnwindPoint !CLabel !UnwindTable

instance Outputable UnwindPoint where
  ppr :: UnwindPoint -> SDoc
ppr (UnwindPoint CLabel
lbl UnwindTable
uws) =
      SDoc -> SDoc
braces (SDoc -> SDoc) -> SDoc -> SDoc
forall a b. (a -> b) -> a -> b
$ CLabel -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type Outputable CLabel
ppr CLabel
lblSDoc -> SDoc -> SDoc
<>SDoc
colon
      SDoc -> SDoc -> SDoc
<+> [SDoc] -> SDoc
hsep (SDoc -> [SDoc] -> [SDoc]
punctuate SDoc
comma ([SDoc] -> [SDoc]) -> [SDoc] -> [SDoc]
forall a b. (a -> b) -> a -> b
$ ((GlobalReg, Maybe UnwindExpr) -> SDoc)
-> [(GlobalReg, Maybe UnwindExpr)] -> [SDoc]
forall a b. (a -> b) -> [a] -> [b]
map (GlobalReg, Maybe UnwindExpr) -> SDoc
forall {a} {a}. (Outputable a, Outputable a) => (a, a) -> SDoc
External instance of the constraint type forall a. Outputable a => Outputable (Maybe a)
Instance of class: Outputable of the constraint type Outputable UnwindExpr
External instance of the constraint type Outputable GlobalReg
pprUw ([(GlobalReg, Maybe UnwindExpr)] -> [SDoc])
-> [(GlobalReg, Maybe UnwindExpr)] -> [SDoc]
forall a b. (a -> b) -> a -> b
$ UnwindTable -> [(GlobalReg, Maybe UnwindExpr)]
forall k a. Map k a -> [(k, a)]
Map.toList UnwindTable
uws)
    where
      pprUw :: (a, a) -> SDoc
pprUw (a
g, a
expr) = a -> SDoc
forall a. Outputable a => a -> SDoc
Evidence bound by a type signature of the constraint type Outputable a
ppr a
g SDoc -> SDoc -> SDoc
<> Char -> SDoc
char Char
'=' SDoc -> SDoc -> SDoc
<> a -> SDoc
forall a. Outputable a => a -> SDoc
Evidence bound by a type signature of the constraint type Outputable a
ppr a
expr

-- | Maps registers to expressions that yield their "old" values
-- further up the stack. Most interesting for the stack pointer @Sp@,
-- but might be useful to document saved registers, too. Note that a
-- register's value will be 'Nothing' when the register's previous
-- value cannot be reconstructed.
type UnwindTable = Map.Map GlobalReg (Maybe UnwindExpr)

-- | Expressions, used for unwind information
data UnwindExpr = UwConst !Int                  -- ^ literal value
                | UwReg !GlobalReg !Int         -- ^ register plus offset
                | UwDeref UnwindExpr            -- ^ pointer dereferencing
                | UwLabel CLabel
                | UwPlus UnwindExpr UnwindExpr
                | UwMinus UnwindExpr UnwindExpr
                | UwTimes UnwindExpr UnwindExpr
                deriving (UnwindExpr -> UnwindExpr -> Bool
(UnwindExpr -> UnwindExpr -> Bool)
-> (UnwindExpr -> UnwindExpr -> Bool) -> Eq UnwindExpr
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
/= :: UnwindExpr -> UnwindExpr -> Bool
$c/= :: UnwindExpr -> UnwindExpr -> Bool
== :: UnwindExpr -> UnwindExpr -> Bool
$c== :: UnwindExpr -> UnwindExpr -> Bool
External instance of the constraint type Eq CLabel
Instance of class: Eq of the constraint type Eq UnwindExpr
External instance of the constraint type Eq GlobalReg
External instance of the constraint type Eq Int
External instance of the constraint type Eq Int
Instance of class: Eq of the constraint type Eq UnwindExpr
Eq)

instance Outputable UnwindExpr where
  pprPrec :: Rational -> UnwindExpr -> SDoc
pprPrec Rational
_ (UwConst Int
i)     = Int -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type Outputable Int
ppr Int
i
  pprPrec Rational
_ (UwReg GlobalReg
g Int
0)     = GlobalReg -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type Outputable GlobalReg
ppr GlobalReg
g
  pprPrec Rational
p (UwReg GlobalReg
g Int
x)     = Rational -> UnwindExpr -> SDoc
forall a. Outputable a => Rational -> a -> SDoc
Instance of class: Outputable of the constraint type Outputable UnwindExpr
pprPrec Rational
p (UnwindExpr -> UnwindExpr -> UnwindExpr
UwPlus (GlobalReg -> Int -> UnwindExpr
UwReg GlobalReg
g Int
0) (Int -> UnwindExpr
UwConst Int
x))
  pprPrec Rational
_ (UwDeref UnwindExpr
e)     = Char -> SDoc
char Char
'*' SDoc -> SDoc -> SDoc
<> Rational -> UnwindExpr -> SDoc
forall a. Outputable a => Rational -> a -> SDoc
Instance of class: Outputable of the constraint type Outputable UnwindExpr
pprPrec Rational
3 UnwindExpr
e
  pprPrec Rational
_ (UwLabel CLabel
l)     = Rational -> CLabel -> SDoc
forall a. Outputable a => Rational -> a -> SDoc
External instance of the constraint type Outputable CLabel
pprPrec Rational
3 CLabel
l
  pprPrec Rational
p (UwPlus UnwindExpr
e0 UnwindExpr
e1)  | Rational
p Rational -> Rational -> Bool
forall a. Ord a => a -> a -> Bool
External instance of the constraint type forall a. Integral a => Ord (Ratio a)
External instance of the constraint type Integral Integer
<= Rational
0
                            = Rational -> UnwindExpr -> SDoc
forall a. Outputable a => Rational -> a -> SDoc
Instance of class: Outputable of the constraint type Outputable UnwindExpr
pprPrec Rational
0 UnwindExpr
e0 SDoc -> SDoc -> SDoc
<> Char -> SDoc
char Char
'+' SDoc -> SDoc -> SDoc
<> Rational -> UnwindExpr -> SDoc
forall a. Outputable a => Rational -> a -> SDoc
Instance of class: Outputable of the constraint type Outputable UnwindExpr
pprPrec Rational
0 UnwindExpr
e1
  pprPrec Rational
p (UwMinus UnwindExpr
e0 UnwindExpr
e1) | Rational
p Rational -> Rational -> Bool
forall a. Ord a => a -> a -> Bool
External instance of the constraint type forall a. Integral a => Ord (Ratio a)
External instance of the constraint type Integral Integer
<= Rational
0
                            = Rational -> UnwindExpr -> SDoc
forall a. Outputable a => Rational -> a -> SDoc
Instance of class: Outputable of the constraint type Outputable UnwindExpr
pprPrec Rational
1 UnwindExpr
e0 SDoc -> SDoc -> SDoc
<> Char -> SDoc
char Char
'-' SDoc -> SDoc -> SDoc
<> Rational -> UnwindExpr -> SDoc
forall a. Outputable a => Rational -> a -> SDoc
Instance of class: Outputable of the constraint type Outputable UnwindExpr
pprPrec Rational
1 UnwindExpr
e1
  pprPrec Rational
p (UwTimes UnwindExpr
e0 UnwindExpr
e1) | Rational
p Rational -> Rational -> Bool
forall a. Ord a => a -> a -> Bool
External instance of the constraint type forall a. Integral a => Ord (Ratio a)
External instance of the constraint type Integral Integer
<= Rational
1
                            = Rational -> UnwindExpr -> SDoc
forall a. Outputable a => Rational -> a -> SDoc
Instance of class: Outputable of the constraint type Outputable UnwindExpr
pprPrec Rational
2 UnwindExpr
e0 SDoc -> SDoc -> SDoc
<> Char -> SDoc
char Char
'*' SDoc -> SDoc -> SDoc
<> Rational -> UnwindExpr -> SDoc
forall a. Outputable a => Rational -> a -> SDoc
Instance of class: Outputable of the constraint type Outputable UnwindExpr
pprPrec Rational
2 UnwindExpr
e1
  pprPrec Rational
_ UnwindExpr
other           = SDoc -> SDoc
parens (Rational -> UnwindExpr -> SDoc
forall a. Outputable a => Rational -> a -> SDoc
Instance of class: Outputable of the constraint type Outputable UnwindExpr
pprPrec Rational
0 UnwindExpr
other)

-- | Conversion of Cmm expressions to unwind expressions. We check for
-- unsupported operator usages and simplify the expression as far as
-- possible.
toUnwindExpr :: Platform -> CmmExpr -> UnwindExpr
toUnwindExpr :: Platform -> CmmExpr -> UnwindExpr
toUnwindExpr Platform
_ (CmmLit (CmmInt Integer
i Width
_))       = Int -> UnwindExpr
UwConst (Integer -> Int
forall a b. (Integral a, Num b) => a -> b
External instance of the constraint type Num Int
External instance of the constraint type Integral Integer
fromIntegral Integer
i)
toUnwindExpr Platform
_ (CmmLit (CmmLabel CLabel
l))       = CLabel -> UnwindExpr
UwLabel CLabel
l
toUnwindExpr Platform
_ (CmmRegOff (CmmGlobal GlobalReg
g) Int
i) = GlobalReg -> Int -> UnwindExpr
UwReg GlobalReg
g Int
i
toUnwindExpr Platform
_ (CmmReg (CmmGlobal GlobalReg
g))      = GlobalReg -> Int -> UnwindExpr
UwReg GlobalReg
g Int
0
toUnwindExpr Platform
platform (CmmLoad CmmExpr
e CmmType
_)               = UnwindExpr -> UnwindExpr
UwDeref (Platform -> CmmExpr -> UnwindExpr
toUnwindExpr Platform
platform CmmExpr
e)
toUnwindExpr Platform
platform e :: CmmExpr
e@(CmmMachOp MachOp
op [CmmExpr
e1, CmmExpr
e2])   =
  case (MachOp
op, Platform -> CmmExpr -> UnwindExpr
toUnwindExpr Platform
platform CmmExpr
e1, Platform -> CmmExpr -> UnwindExpr
toUnwindExpr Platform
platform CmmExpr
e2) of
    (MO_Add{}, UwReg GlobalReg
r Int
x, UwConst Int
y) -> GlobalReg -> Int -> UnwindExpr
UwReg GlobalReg
r (Int
x Int -> Int -> Int
forall a. Num a => a -> a -> a
External instance of the constraint type Num Int
+ Int
y)
    (MO_Sub{}, UwReg GlobalReg
r Int
x, UwConst Int
y) -> GlobalReg -> Int -> UnwindExpr
UwReg GlobalReg
r (Int
x Int -> Int -> Int
forall a. Num a => a -> a -> a
External instance of the constraint type Num Int
- Int
y)
    (MO_Add{}, UwConst Int
x, UwReg GlobalReg
r Int
y) -> GlobalReg -> Int -> UnwindExpr
UwReg GlobalReg
r (Int
x Int -> Int -> Int
forall a. Num a => a -> a -> a
External instance of the constraint type Num Int
+ Int
y)
    (MO_Add{}, UwConst Int
x, UwConst Int
y) -> Int -> UnwindExpr
UwConst (Int
x Int -> Int -> Int
forall a. Num a => a -> a -> a
External instance of the constraint type Num Int
+ Int
y)
    (MO_Sub{}, UwConst Int
x, UwConst Int
y) -> Int -> UnwindExpr
UwConst (Int
x Int -> Int -> Int
forall a. Num a => a -> a -> a
External instance of the constraint type Num Int
- Int
y)
    (MO_Mul{}, UwConst Int
x, UwConst Int
y) -> Int -> UnwindExpr
UwConst (Int
x Int -> Int -> Int
forall a. Num a => a -> a -> a
External instance of the constraint type Num Int
* Int
y)
    (MO_Add{}, UnwindExpr
u1,        UnwindExpr
u2       ) -> UnwindExpr -> UnwindExpr -> UnwindExpr
UwPlus UnwindExpr
u1 UnwindExpr
u2
    (MO_Sub{}, UnwindExpr
u1,        UnwindExpr
u2       ) -> UnwindExpr -> UnwindExpr -> UnwindExpr
UwMinus UnwindExpr
u1 UnwindExpr
u2
    (MO_Mul{}, UnwindExpr
u1,        UnwindExpr
u2       ) -> UnwindExpr -> UnwindExpr -> UnwindExpr
UwTimes UnwindExpr
u1 UnwindExpr
u2
    (MachOp, UnwindExpr, UnwindExpr)
_otherwise -> String -> SDoc -> UnwindExpr
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"Unsupported operator in unwind expression!"
                           (Platform -> CmmExpr -> SDoc
pprExpr Platform
platform CmmExpr
e)
toUnwindExpr Platform
_ CmmExpr
e
  = String -> SDoc -> UnwindExpr
forall a. HasCallStack => String -> SDoc -> a
pprPanic String
"Unsupported unwind expression!" (CmmExpr -> SDoc
forall a. Outputable a => a -> SDoc
External instance of the constraint type Outputable CmmExpr
ppr CmmExpr
e)