Perform unaligned writes via FFI when necessary

Data/ByteString/Builder/Prim/Binary.hs

@@ -1,5 +1,8 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE Trustworthy #-}
+
+{-# LANGUAGE TypeApplications #-}
+
 -- | Copyright   : (c) 2010-2011 Simon Meier
 -- License       : BSD3-style (see LICENSE)
 --
@@ -70,7 +73,7 @@ import Foreign
 --
 {-# INLINE word8 #-}
 word8 :: FixedPrim Word8
-word8 = storableToF
+word8 = fixedPrim 1 (flip poke) -- Word8 is always aligned
 
 --
 -- We rely on the fromIntegral to do the right masking for us.
@@ -143,23 +146,43 @@ word64LE = word64Host
 --
 {-# INLINE wordHost #-}
 wordHost :: FixedPrim Word
-wordHost = storableToF
+wordHost = case finiteBitSize (0 :: Word) of
+  32 -> fromIntegral @Word @Word32 >$< word32Host
+  64 -> fromIntegral @Word @Word64 >$< word64Host
+  _ -> error "Data.ByteString.Builder.Prim.Binary.wordHost: unexpected word size"
 
 -- | Encoding 'Word16's in native host order and host endianness.
 {-# INLINE word16Host #-}
 word16Host :: FixedPrim Word16
-word16Host = storableToF
+word16Host = fixedPrim 2 unaligned_write_u16
 
 -- | Encoding 'Word32's in native host order and host endianness.
 {-# INLINE word32Host #-}
 word32Host :: FixedPrim Word32
-word32Host = storableToF
+word32Host = fixedPrim 4 unaligned_write_u32
 
 -- | Encoding 'Word64's in native host order and host endianness.
 {-# INLINE word64Host #-}
 word64Host :: FixedPrim Word64
-word64Host = storableToF
+word64Host = fixedPrim 8 unaligned_write_u64
+
+#if HS_BYTESTRING_UNALIGNED_POKES_OK
+unaligned_write_u16 :: Word16 -> Ptr Word8 -> IO ()
+unaligned_write_u16 x p = poke (castPtr p) x
 
+unaligned_write_u32 :: Word32 -> Ptr Word8 -> IO ()
+unaligned_write_u32 x p = poke (castPtr p) x
+
+unaligned_write_u64 :: Word64 -> Ptr Word8 -> IO ()
+unaligned_write_u64 x p = poke (castPtr p) x
+#else
+foreign import ccall unsafe "static fpstring.h fps_unaligned_write_u16"
+  unaligned_write_u16 :: Word16 -> Ptr Word8 -> IO ()
+foreign import ccall unsafe "static fpstring.h fps_unaligned_write_u32"
+  unaligned_write_u32 :: Word32 -> Ptr Word8 -> IO ()
+foreign import ccall unsafe "static fpstring.h fps_unaligned_write_u64"
+  unaligned_write_u64 :: Word64 -> Ptr Word8 -> IO ()
+#endif
 
 ------------------------------------------------------------------------------
 -- Int encodings
@@ -215,22 +238,22 @@ int64LE = fromIntegral >$< word64LE
 --
 {-# INLINE intHost #-}
 intHost :: FixedPrim Int
-intHost = storableToF
+intHost = fromIntegral @Int @Word >$< wordHost
 
 -- | Encoding 'Int16's in native host order and host endianness.
 {-# INLINE int16Host #-}
 int16Host :: FixedPrim Int16
-int16Host = storableToF
+int16Host = fromIntegral @Int16 @Word16 >$< word16Host
 
 -- | Encoding 'Int32's in native host order and host endianness.
 {-# INLINE int32Host #-}
 int32Host :: FixedPrim Int32
-int32Host = storableToF
+int32Host = fromIntegral @Int32 @Word32 >$< word32Host
 
 -- | Encoding 'Int64's in native host order and host endianness.
 {-# INLINE int64Host #-}
 int64Host :: FixedPrim Int64
-int64Host = storableToF
+int64Host = fromIntegral @Int64 @Word64 >$< word64Host
 
 -- IEEE Floating Point Numbers
 ------------------------------

Data/ByteString/Builder/Prim/Internal.hs

@@ -73,6 +73,7 @@ import Foreign
 import Prelude hiding (maxBound)
 
 #include "MachDeps.h"
+#include "bytestring-cpp-macros.h"
 
 ------------------------------------------------------------------------------
 -- Supporting infrastructure
@@ -199,13 +200,7 @@ liftFixedToBounded = toB
 
 {-# INLINE CONLIKE storableToF #-}
 storableToF :: forall a. Storable a => FixedPrim a
--- Not all architectures are forgiving of unaligned accesses; whitelist ones
--- which are known not to trap (either to the kernel for emulation, or crash).
-#if defined(i386_HOST_ARCH) || defined(x86_64_HOST_ARCH) \
-    || ((defined(arm_HOST_ARCH) || defined(aarch64_HOST_ARCH)) \
-        && defined(__ARM_FEATURE_UNALIGNED)) \
-    || defined(powerpc_HOST_ARCH) || defined(powerpc64_HOST_ARCH) \
-    || defined(powerpc64le_HOST_ARCH)
+#if HS_UNALIGNED_POKES_OK
 storableToF = FP (sizeOf (undefined :: a)) (\x op -> poke (castPtr op) x)
 #else
 storableToF = FP (sizeOf (undefined :: a)) $ \x op ->

Data/ByteString/Short/Internal.hs

@@ -21,15 +21,8 @@
 {-# OPTIONS_HADDOCK not-home #-}
 
 {-# OPTIONS_GHC -fexpose-all-unfoldings #-}
--- Not all architectures are forgiving of unaligned accesses; whitelist ones
--- which are known not to trap (either to the kernel for emulation, or crash).
-#if defined(i386_HOST_ARCH) || defined(x86_64_HOST_ARCH) \
-    || ((defined(arm_HOST_ARCH) || defined(aarch64_HOST_ARCH)) \
-        && defined(__ARM_FEATURE_UNALIGNED)) \
-    || defined(powerpc_HOST_ARCH) || defined(powerpc64_HOST_ARCH) \
-    || defined(powerpc64le_HOST_ARCH)
-#define SAFE_UNALIGNED 1
-#endif
+
+#include "bytestring-cpp-macros.h"
 
 -- |
 -- Module      : Data.ByteString.Short.Internal
@@ -172,7 +165,7 @@ import Data.Array.Byte
 import Data.Bits
   ( FiniteBits (finiteBitSize)
   , shiftL
-#if MIN_VERSION_base(4,12,0) && defined(SAFE_UNALIGNED)
+#if HS_UNALIGNED_ByteArray_OPS_OK
   , shiftR
 #endif
   , (.&.)
@@ -231,7 +224,7 @@ import GHC.Exts
   , indexWord8Array#, indexCharArray#
   , writeWord8Array#
   , unsafeFreezeByteArray#
-#if MIN_VERSION_base(4,12,0) && defined(SAFE_UNALIGNED)
+#if HS_UNALIGNED_ByteArray_OPS_OK
   ,writeWord64Array#
   ,indexWord8ArrayAsWord64#
 #endif
@@ -803,8 +796,7 @@ reverse :: ShortByteString -> ShortByteString
 reverse = \sbs ->
     let l  = length sbs
         ba = asBA sbs
--- https://gitlab.haskell.org/ghc/ghc/-/issues/21015
-#if MIN_VERSION_base(4,12,0) && defined(SAFE_UNALIGNED)
+#if HS_UNALIGNED_ByteArray_OPS_OK
     in create l (\mba -> go ba mba l)
   where
     go :: forall s. BA -> MBA s -> Int -> ST s ()
@@ -1607,7 +1599,7 @@ indexCharArray (BA# ba#) (I# i#) = C# (indexCharArray# ba# i#)
 indexWord8Array :: BA -> Int -> Word8
 indexWord8Array (BA# ba#) (I# i#) = W8# (indexWord8Array# ba# i#)
 
-#if MIN_VERSION_base(4,12,0) && defined(SAFE_UNALIGNED)
+#if HS_UNALIGNED_ByteArray_OPS_OK
 indexWord8ArrayAsWord64 :: BA -> Int -> Word64
 indexWord8ArrayAsWord64 (BA# ba#) (I# i#) = W64# (indexWord8ArrayAsWord64# ba# i#)
 #endif
@@ -1632,7 +1624,7 @@ writeWord8Array (MBA# mba#) (I# i#) (W8# w#) =
   ST $ \s -> case writeWord8Array# mba# i# w# s of
                s' -> (# s', () #)
 
-#if MIN_VERSION_base(4,12,0) && defined(SAFE_UNALIGNED)
+#if HS_UNALIGNED_ByteArray_OPS_OK
 writeWord64Array :: MBA s -> Int -> Word64 -> ST s ()
 writeWord64Array (MBA# mba#) (I# i#) (W64# w#) =
   ST $ \s -> case writeWord64Array# mba# i# w# s of

bytestring.cabal

@@ -128,19 +128,19 @@ library
                     -fmax-simplifier-iterations=10
                     -fdicts-cheap
                     -fspec-constr-count=6
-  
+
   c-sources:        cbits/fpstring.c
                     cbits/itoa.c
                     cbits/shortbytestring.c
-  
+
   if (arch(aarch64))
     c-sources:        cbits/aarch64/is-valid-utf8.c
   else
     c-sources:        cbits/is-valid-utf8.c
-  
+
   -- DNDEBUG disables asserts in cbits/
   cc-options:        -std=c11 -DNDEBUG=1
- 
+
   -- No need to link to libgcc on ghc-9.4 and later which uses a clang-based
   -- toolchain.
   if os(windows) && impl(ghc < 9.3)

cbits/fpstring.c

@@ -43,6 +43,8 @@
 #define USE_SIMD_COUNT
 #endif
 
+#include "bytestring-cpp-macros.h"
+
 /* copy a string in reverse */
 void fps_reverse(unsigned char *q, unsigned char *p, size_t n) {
     p += n-1;
@@ -106,6 +108,23 @@ void fps_sort(unsigned char *p, size_t len) {
     return qsort(p, len, 1, fps_compare);
 }
 
+#if !HS_UNALIGNED_POKES_OK
+void fps_unaligned_write_u16(uint16_t x, uint8_t *p) {
+  memcpy(p, &x, 2);
+  return;
+}
+
+void fps_unaligned_write_u32(uint32_t x, uint8_t *p) {
+  memcpy(p, &x, 4);
+  return;
+}
+
+void fps_unaligned_write_u64(uint64_t x, uint8_t *p) {
+  memcpy(p, &x, 8);
+  return;
+}
+#endif
+
 /* count the number of occurrences of a char in a string */
 size_t fps_count_naive(unsigned char *str, size_t len, unsigned char w) {
     size_t c;

include/bytestring-cpp-macros.h

@@ -0,0 +1,27 @@
+#if 0
+This file gets included in both C and Haskell sources,
+so any comments should by guarded by an if 0.
+#endif
+
+
+
+#define HS_UNALIGNED_POKES_OK \
+  defined(i386_HOST_ARCH) || defined(x86_64_HOST_ARCH)         \
+    || ((defined(arm_HOST_ARCH) || defined(aarch64_HOST_ARCH)) \
+        && defined(__ARM_FEATURE_UNALIGNED)) \
+    || defined(powerpc_HOST_ARCH) || defined(powerpc64_HOST_ARCH) \
+    || defined(powerpc64le_HOST_ARCH)
+#if 0
+Not all architectures are forgiving of unaligned accesses; whitelist ones
+which are known not to trap (either to the kernel for emulation, or crash).
+#endif
+
+
+#define HS_UNALIGNED_ByteArray_OPS_OK \
+  MIN_VERSION_base(4,12,0) \
+  && (MIN_VERSION_base(4,16,1) || UNALIGNED_POKES_OK)
+#if 0
+The unaligned ByteArray# primops became available with base-4.12.0,
+but require an unaligned-friendly host architecture to be safe to use
+until ghc-9.2.2; see https://gitlab.haskell.org/ghc/ghc/-/issues/21015
+#endif