dist-install/build/GHC/ExecutionStack/Internal.hs

{-# LINE 1 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}
-----------------------------------------------------------------------------
-- |
-- Module : GHC.ExecutionStack.Internal
-- Copyright : (c) The University of Glasgow 2013-2015
-- License : see libraries/base/LICENSE
--
-- Maintainer : cvs-ghc@haskell.org
-- Stability : internal
-- Portability : non-portable (GHC Extensions)
--
-- Internals of the `GHC.ExecutionStack` module
--
-- @since 4.9.0.0
-----------------------------------------------------------------------------





{-# LANGUAGE MultiWayIf #-}

module GHC.ExecutionStack.Internal (
 -- * Internal
 Location (..)
 , SrcLoc (..)
 , StackTrace
 , stackFrames
 , stackDepth
 , collectStackTrace
 , showStackFrames
 , invalidateDebugCache
 ) where

import Control.Monad (join)
import Data.Word
import Foreign.C.Types
import Foreign.C.String (peekCString, CString)
import Foreign.Ptr (Ptr, nullPtr, castPtr, plusPtr, FunPtr)
import Foreign.ForeignPtr
import Foreign.Marshal.Alloc (allocaBytes)
import Foreign.Storable (Storable(..))
import System.IO.Unsafe (unsafePerformIO, unsafeInterleaveIO)

-- N.B. See includes/rts/Libdw.h for notes on stack representation.

-- | A location in the original program source.
data SrcLoc = SrcLoc { sourceFile :: String
 , sourceLine :: Int
 , sourceColumn :: Int
 }

-- | Location information about an address from a backtrace.
data Location = Location { objectName :: String
 , functionName :: String
 , srcLoc :: Maybe SrcLoc
 }

-- | A chunk of backtrace frames
data Chunk = Chunk { chunkFrames :: !Word
 , chunkNext :: !(Ptr Chunk)
 , chunkFirstFrame :: !(Ptr Addr)
 }

-- | The state of the execution stack
newtype StackTrace = StackTrace (ForeignPtr StackTrace)

-- | An address
type Addr = Ptr ()

withSession :: (ForeignPtr Session -> IO a) -> IO (Maybe a)
withSession action = do
 ptr <- libdw_pool_take
 if | nullPtr == ptr -> return Nothing
 | otherwise -> do
 fptr <- newForeignPtr libdw_pool_release ptr
 ret <- action fptr
 return $ Just ret

-- | How many stack frames in the given 'StackTrace'
stackDepth :: StackTrace -> Int
stackDepth (StackTrace fptr) =
 unsafePerformIO $ withForeignPtr fptr $ \ptr ->
 fromIntegral . asWord <$> ((\hsc_ptr -> peekByteOff hsc_ptr 0)) ptr
{-# LINE 84 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}
 where
 asWord = id :: Word -> Word

peekChunk :: Ptr Chunk -> IO Chunk
peekChunk ptr =
 Chunk <$> ((\hsc_ptr -> peekByteOff hsc_ptr 0)) ptr
{-# LINE 90 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}
 <*> ((\hsc_ptr -> peekByteOff hsc_ptr 8)) ptr
{-# LINE 91 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}
 <*> pure (castPtr $ ((\hsc_ptr -> hsc_ptr `plusPtr` 16)) ptr)
{-# LINE 92 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}

-- | Return a list of the chunks of a backtrace, from the outer-most to
-- inner-most chunk.
chunksList :: StackTrace -> IO [Chunk]
chunksList (StackTrace fptr) = withForeignPtr fptr $ \ptr ->
 go [] =<< ((\hsc_ptr -> peekByteOff hsc_ptr 8)) ptr
{-# LINE 98 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}
 where
 go accum ptr
 | ptr == nullPtr = return accum
 | otherwise = do
 chunk <- peekChunk ptr
 go (chunk : accum) (chunkNext chunk)

-- | Unpack the given 'Location' in the Haskell representation
peekLocation :: Ptr Location -> IO Location
peekLocation ptr = do
 let peekCStringPtr :: CString -> IO String
 peekCStringPtr p
 | p /= nullPtr = peekCString $ castPtr p
 | otherwise = return ""
 objFile <- peekCStringPtr =<< ((\hsc_ptr -> peekByteOff hsc_ptr 0)) ptr
{-# LINE 113 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}
 function <- peekCStringPtr =<< ((\hsc_ptr -> peekByteOff hsc_ptr 8)) ptr
{-# LINE 114 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}
 srcFile <- peekCStringPtr =<< ((\hsc_ptr -> peekByteOff hsc_ptr 16)) ptr
{-# LINE 115 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}
 lineNo <- ((\hsc_ptr -> peekByteOff hsc_ptr 24)) ptr :: IO Word32
{-# LINE 116 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}
 colNo <- ((\hsc_ptr -> peekByteOff hsc_ptr 28)) ptr :: IO Word32
{-# LINE 117 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}
 let _srcLoc
 | null srcFile = Nothing
 | otherwise = Just $ SrcLoc { sourceFile = srcFile
 , sourceLine = fromIntegral lineNo
 , sourceColumn = fromIntegral colNo
 }
 return Location { objectName = objFile
 , functionName = function
 , srcLoc = _srcLoc
 }

-- | The size in bytes of a 'locationSize'
locationSize :: Int
locationSize = (32)
{-# LINE 131 "libraries/base/GHC/ExecutionStack/Internal.hsc" #-}

-- | List the frames of a stack trace.
stackFrames :: StackTrace -> Maybe [Location]
stackFrames st@(StackTrace fptr) = unsafePerformIO $ withSession $ \sess -> do
 chunks <- chunksList st
 go sess (reverse chunks)
 where
 go :: ForeignPtr Session -> [Chunk] -> IO [Location]
 go _ [] = return []
 go sess (chunk : chunks) = do
 this <- iterChunk sess chunk
 rest <- unsafeInterleaveIO (go sess chunks)
 return (this ++ rest)

 {-
 Here we lazily lookup the location information associated with each address
 as this can be rather costly. This does mean, however, that if the set of
 loaded modules changes between the time that we capture the stack and the
 time we reach here, we may end up with nonsense (mostly likely merely
 unknown symbols). I think this is a reasonable price to pay, however, as
 module loading/unloading is a rather rare event.

 Morover, we stand to gain a great deal by lazy lookups as the stack frames
 may never even be requested, meaning the only effort wasted is the
 collection of the stack frames themselves.

 The only slightly tricky thing here is to ensure that the ForeignPtr
 stays alive until we reach the end.
 -}
 iterChunk :: ForeignPtr Session -> Chunk -> IO [Location]
 iterChunk sess chunk = iterFrames (chunkFrames chunk) (chunkFirstFrame chunk)
 where
 iterFrames :: Word -> Ptr Addr -> IO [Location]
 iterFrames 0 _ = return []
 iterFrames n frame = do
 pc <- peek frame :: IO Addr
 mframe <- lookupFrame pc
 rest <- unsafeInterleaveIO (iterFrames (n-1) frame')
 return $ maybe rest (:rest) mframe
 where
 frame' = frame `plusPtr` sizeOf (undefined :: Addr)

 lookupFrame :: Addr -> IO (Maybe Location)
 lookupFrame pc = withForeignPtr fptr $ const $ do
 allocaBytes locationSize $ \buf -> do
 ret <- withForeignPtr sess $ \sessPtr -> libdw_lookup_location sessPtr buf pc
 case ret of
 0 -> Just <$> peekLocation buf
 _ -> return Nothing

-- | A LibdwSession from the runtime system
data Session

foreign import ccall unsafe "libdwPoolTake"
 libdw_pool_take :: IO (Ptr Session)

foreign import ccall unsafe "&libdwPoolRelease"
 libdw_pool_release :: FunPtr (Ptr Session -> IO ())

foreign import ccall unsafe "libdwPoolClear"
 libdw_pool_clear :: IO ()

foreign import ccall unsafe "libdwLookupLocation"
 libdw_lookup_location :: Ptr Session -> Ptr Location -> Addr -> IO CInt

foreign import ccall unsafe "libdwGetBacktrace"
 libdw_get_backtrace :: Ptr Session -> IO (Ptr StackTrace)

foreign import ccall unsafe "&backtraceFree"
 backtrace_free :: FunPtr (Ptr StackTrace -> IO ())

-- | Get an execution stack.
collectStackTrace :: IO (Maybe StackTrace)
collectStackTrace = fmap join $ withSession $ \sess -> do
 st <- withForeignPtr sess libdw_get_backtrace
 if | st == nullPtr -> return Nothing
 | otherwise -> Just . StackTrace <$> newForeignPtr backtrace_free st

-- | Free the cached debug data.
invalidateDebugCache :: IO ()
invalidateDebugCache = libdw_pool_clear

-- | Render a stacktrace as a string
showStackFrames :: [Location] -> ShowS
showStackFrames frames =
 showString "Stack trace:\n"
 . foldr (.) id (map showFrame frames)
 where
 showFrame loc =
 showString " " . showLocation loc . showChar '\n'

-- | Render a 'Location' as a string
showLocation :: Location -> ShowS
showLocation loc =
 showString (functionName loc)
 . maybe id showSrcLoc (srcLoc loc)
 . showString " in "
 . showString (objectName loc)
 where
 showSrcLoc :: SrcLoc -> ShowS
 showSrcLoc sloc =
 showString " ("
 . showString (sourceFile sloc)
 . showString ":"
 . shows (sourceLine sloc)
 . showString "."
 . shows (sourceColumn sloc)
 . showString ")"