[Git][ghc/ghc][wip/T22043] CApiFFI: add ConstPtr for encoding const-qualified pointer return types
Matthew Pickering (@mpickering)
gitlab at gitlab.haskell.org
Mon Jan 23 08:35:46 UTC 2023
Matthew Pickering pushed to branch wip/T22043 at Glasgow Haskell Compiler / GHC
Commits:
9a24241f by nineonine at 2023-01-23T08:34:30+00:00
CApiFFI: add ConstPtr for encoding const-qualified pointer return types
Previously, when using `capi` calling convention in foreign declarations,
code generator failed to handle const-cualified pointer return types.
This resulted in CC toolchain throwing `-Wincompatible-pointer-types-discards-qualifiers`
warning.
`Foreign.C.Types.ConstPtr` newtype was introduced to handle these cases -
special treatment was put in place to generate appropritetly qualified C
wrapper that no longer triggers the above mentioned warning.
Fixes #22043.
- - - - -
14 changed files:
- compiler/GHC/Builtin/Names.hs
- compiler/GHC/HsToCore/Foreign/C.hs
- docs/users_guide/9.6.1-notes.rst
- docs/users_guide/exts/ffi.rst
- libraries/base/Data/Data.hs
- + libraries/base/Foreign/C/ConstPtr.hs
- libraries/base/Foreign/C/Types.hs
- libraries/base/Foreign/Storable.hs
- libraries/base/base.cabal
- libraries/base/changelog.md
- + testsuite/tests/ffi/should_compile/T22043.h
- + testsuite/tests/ffi/should_compile/T22043.hs
- + testsuite/tests/ffi/should_compile/T22043_c.c
- testsuite/tests/ffi/should_compile/all.T
Changes:
=====================================
compiler/GHC/Builtin/Names.hs
=====================================
@@ -350,7 +350,7 @@ basicKnownKeyNames
zipName, foldrName, buildName, augmentName, appendName,
-- FFI primitive types that are not wired-in.
- stablePtrTyConName, ptrTyConName, funPtrTyConName,
+ stablePtrTyConName, ptrTyConName, funPtrTyConName, constPtrConName,
int8TyConName, int16TyConName, int32TyConName, int64TyConName,
word8TyConName, word16TyConName, word32TyConName, word64TyConName,
@@ -557,7 +557,7 @@ gHC_PRIM, gHC_PRIM_PANIC,
aRROW, gHC_DESUGAR, rANDOM, gHC_EXTS, gHC_IS_LIST,
cONTROL_EXCEPTION_BASE, gHC_TYPEERROR, gHC_TYPELITS, gHC_TYPELITS_INTERNAL,
gHC_TYPENATS, gHC_TYPENATS_INTERNAL,
- dATA_COERCE, dEBUG_TRACE, uNSAFE_COERCE :: Module
+ dATA_COERCE, dEBUG_TRACE, uNSAFE_COERCE, fOREIGN_C_CONSTPTR :: Module
gHC_PRIM = mkPrimModule (fsLit "GHC.Prim") -- Primitive types and values
gHC_PRIM_PANIC = mkPrimModule (fsLit "GHC.Prim.Panic")
@@ -626,6 +626,7 @@ gHC_TYPENATS_INTERNAL = mkBaseModule (fsLit "GHC.TypeNats.Internal")
dATA_COERCE = mkBaseModule (fsLit "Data.Coerce")
dEBUG_TRACE = mkBaseModule (fsLit "Debug.Trace")
uNSAFE_COERCE = mkBaseModule (fsLit "Unsafe.Coerce")
+fOREIGN_C_CONSTPTR = mkBaseModule (fsLit "Foreign.C.ConstPtr")
gHC_SRCLOC :: Module
gHC_SRCLOC = mkBaseModule (fsLit "GHC.SrcLoc")
@@ -1664,6 +1665,10 @@ fingerprintDataConName :: Name
fingerprintDataConName =
dcQual gHC_FINGERPRINT_TYPE (fsLit "Fingerprint") fingerprintDataConKey
+constPtrConName :: Name
+constPtrConName =
+ tcQual fOREIGN_C_CONSTPTR (fsLit "ConstPtr") constPtrTyConKey
+
{-
************************************************************************
* *
@@ -1865,7 +1870,7 @@ statePrimTyConKey, stableNamePrimTyConKey, stableNameTyConKey,
funPtrTyConKey, tVarPrimTyConKey, eqPrimTyConKey,
eqReprPrimTyConKey, eqPhantPrimTyConKey,
compactPrimTyConKey, stackSnapshotPrimTyConKey,
- promptTagPrimTyConKey :: Unique
+ promptTagPrimTyConKey, constPtrTyConKey :: Unique
statePrimTyConKey = mkPreludeTyConUnique 50
stableNamePrimTyConKey = mkPreludeTyConUnique 51
stableNameTyConKey = mkPreludeTyConUnique 52
@@ -2076,6 +2081,7 @@ typeConsSymbolTyFamNameKey = mkPreludeTyConUnique 413
typeUnconsSymbolTyFamNameKey = mkPreludeTyConUnique 414
typeCharToNatTyFamNameKey = mkPreludeTyConUnique 415
typeNatToCharTyFamNameKey = mkPreludeTyConUnique 416
+constPtrTyConKey = mkPreludeTyConUnique 417
{-
************************************************************************
=====================================
compiler/GHC/HsToCore/Foreign/C.hs
=====================================
@@ -246,10 +246,18 @@ dsFCall :: Id -> Coercion -> ForeignCall -> Maybe Header
-> DsM ([(Id, Expr TyVar)], CHeader, CStub)
dsFCall fn_id co fcall mDeclHeader = do
let
- ty = coercionLKind co
+ (ty,ty1) = (coercionLKind co, coercionRKind co)
(tv_bndrs, rho) = tcSplitForAllTyVarBinders ty
(arg_tys, io_res_ty) = tcSplitFunTys rho
+ let constQual -- provide 'const' qualifier (#22043)
+ | (_, res_ty1) <- tcSplitFunTys ty1
+ , newty <- maybe res_ty1 snd (tcSplitIOType_maybe res_ty1)
+ , Just (ptr, _) <- splitTyConApp_maybe newty
+ , tyConName ptr == constPtrConName
+ = text "const"
+ | otherwise = empty
+
args <- newSysLocalsDs arg_tys -- no FFI representation polymorphism
(val_args, arg_wrappers) <- mapAndUnzipM unboxArg (map Var args)
@@ -277,7 +285,7 @@ dsFCall fn_id co fcall mDeclHeader = do
includes = vcat [ text "#include \"" <> ftext h
<> text "\""
| Header _ h <- nub headers ]
- fun_proto = cResType <+> pprCconv <+> ppr wrapperName <> parens argTypes
+ fun_proto = constQual <+> cResType <+> pprCconv <+> ppr wrapperName <> parens argTypes
cRet
| isVoidRes = cCall
| otherwise = text "return" <+> cCall
=====================================
docs/users_guide/9.6.1-notes.rst
=====================================
@@ -163,6 +163,9 @@ Runtime system
``ghc`` library
~~~~~~~~~~~~~~~
+- Add `Foreign.C.Types.ConstPtr` was added to encode ``const``-qualified pointer return
+ types in foreign declarations when using ``CApiFFI`` extension.
+
``ghc-heap`` library
~~~~~~~~~~~~~~~~~~~~
=====================================
docs/users_guide/exts/ffi.rst
=====================================
@@ -437,6 +437,18 @@ specified. The syntax looks like: ::
data {-# CTYPE "unistd.h" "useconds_t" #-} T = ...
newtype {-# CTYPE "useconds_t" #-} T = ...
+In case foreign declarations contain ``const``-qualified pointer return
+type, ``ConstPtr`` from :base-ref:`Foreign.C.ConstPtr` may be used to
+encode this, e.g. ::
+
+ foreign import capi "header.h f" f :: CInt -> ConstPtr CInt
+
+which corresponds to
+
+.. code-block:: c
+
+ const *int f(int);
+
``hs_thread_done()``
~~~~~~~~~~~~~~~~~~~~
=====================================
libraries/base/Data/Data.hs
=====================================
@@ -140,6 +140,7 @@ import Data.Word -- So we can give Data instance for Word8, ...
import GHC.Real -- So we can give Data instance for Ratio
--import GHC.IOBase -- So we can give Data instance for IO, Handle
import GHC.Ptr -- So we can give Data instance for Ptr
+import Foreign.C.ConstPtr -- So we can give Data instance for ConstPtr
import GHC.ForeignPtr -- So we can give Data instance for ForeignPtr
import Foreign.Ptr (IntPtr(..), WordPtr(..))
-- So we can give Data instance for IntPtr and WordPtr
@@ -1227,6 +1228,9 @@ instance Data a => Data (Ptr a) where
dataTypeOf _ = mkNoRepType "GHC.Ptr.Ptr"
dataCast1 x = gcast1 x
+-- | @since 4.18.0.0
+deriving instance Data a => Data (ConstPtr a)
+
------------------------------------------------------------------------------
-- | @since 4.8.0.0
=====================================
libraries/base/Foreign/C/ConstPtr.hs
=====================================
@@ -0,0 +1,45 @@
+{-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE RoleAnnotations #-}
+{-# LANGUAGE StandaloneKindSignatures #-}
+{-# LANGUAGE Trustworthy #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module : Foreign.C.ConstPtr
+-- Copyright : (c) GHC Developers
+-- License : BSD-style (see the file libraries/base/LICENSE)
+--
+-- Maintainer : ffi at haskell.org
+-- Stability : provisional
+-- Portability : portable
+--
+-- This module provides typed @const@ pointers to foreign data. It is part
+-- of the Foreign Function Interface (FFI).
+--
+-----------------------------------------------------------------------------
+
+module Foreign.C.ConstPtr (
+ ConstPtr(..)
+) where
+
+import GHC.Base
+import GHC.Ptr
+import GHC.Show
+
+-- | A pointer with the C @const@ qualifier. For instance, an argument of type
+-- @ConstPtr CInt@ would be marshalled as @const int*@.
+--
+-- While @const at -ness generally does not matter for @ccall@ imports (since
+-- @const@ and non- at const@ pointers typically have equivalent calling
+-- conventions), it does matter for @capi@ imports. See GHC #22043.
+--
+-- @since 4.18.0.0
+--
+type ConstPtr :: Type -> Type
+type role ConstPtr phantom
+newtype ConstPtr a = ConstPtr { unConstPtr :: Ptr a }
+ deriving (Eq, Ord)
+
+-- doesn't use record syntax
+instance Show (ConstPtr a) where
+ showsPrec d (ConstPtr p) = showParen (d > 10) $ showString "ConstPtr " . showsPrec 11 p
=====================================
libraries/base/Foreign/C/Types.hs
=====================================
@@ -86,8 +86,11 @@ module Foreign.C.Types
-- Instances of: Eq and Storable
, CFile, CFpos, CJmpBuf
+
+ , ConstPtr(..)
) where
+import Foreign.Ptr ( Ptr )
import Foreign.Storable
import Data.Bits ( Bits(..), FiniteBits(..) )
import Data.Int ( Int8, Int16, Int32, Int64 )
@@ -223,6 +226,9 @@ INTEGRAL_TYPE(CUIntPtr,"uintptr_t",HTYPE_UINTPTR_T)
INTEGRAL_TYPE(CIntMax,"intmax_t",HTYPE_INTMAX_T)
INTEGRAL_TYPE(CUIntMax,"uintmax_t",HTYPE_UINTMAX_T)
+-- | Used to produce 'const' qualifier in C code generator
+newtype ConstPtr a = ConstPtr { unConstPtr :: Ptr a } deriving newtype (Show, Eq, Storable)
+
-- C99 types which are still missing include:
-- wint_t, wctrans_t, wctype_t
=====================================
libraries/base/Foreign/Storable.hs
=====================================
@@ -1,5 +1,8 @@
{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE CPP, NoImplicitPrelude, ScopedTypeVariables, BangPatterns #-}
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE StandaloneDeriving #-}
-----------------------------------------------------------------------------
-- |
@@ -42,6 +45,7 @@ import GHC.Word
import GHC.Ptr
import GHC.Base
import GHC.Fingerprint.Type
+import Foreign.C.ConstPtr
import Data.Bits
import GHC.Real
@@ -280,3 +284,5 @@ pokeFingerprint p0 (Fingerprint high low) = do
pokeW64 (castPtr p0) 8 high
pokeW64 (castPtr p0 `plusPtr` 8) 8 low
+
+deriving newtype instance Storable (ConstPtr a)
=====================================
libraries/base/base.cabal
=====================================
@@ -169,6 +169,7 @@ Library
Debug.Trace
Foreign
Foreign.C
+ Foreign.C.ConstPtr
Foreign.C.Error
Foreign.C.String
Foreign.C.Types
=====================================
libraries/base/changelog.md
=====================================
@@ -1,6 +1,9 @@
# Changelog for [`base` package](http://hackage.haskell.org/package/base)
## 4.18.0.0 *TBA*
+
+ * `Foreign.C.ConstPtr.ConstrPtr` was added to encode `const`-qualified
+ pointer types in foreign declarations when using `CApiFFI` extension.
* Add `forall a. Functor (p a)` superclass for `Bifunctor p`.
* Add Functor instances for `(,,,,) a b c d`, `(,,,,,) a b c d e` and
`(,,,,,) a b c d e f`.
=====================================
testsuite/tests/ffi/should_compile/T22043.h
=====================================
@@ -0,0 +1,2 @@
+const int *foo();
+const double *bar;
=====================================
testsuite/tests/ffi/should_compile/T22043.hs
=====================================
@@ -0,0 +1,10 @@
+{-# LANGUAGE CApiFFI #-}
+module T22043 where
+
+import Foreign.C.Types
+
+foreign import capi "T22043.h foo"
+ c_foo :: IO (ConstPtr CInt)
+
+foreign import capi "T22043.h value bar"
+ c_bar :: ConstPtr CDouble
=====================================
testsuite/tests/ffi/should_compile/T22043_c.c
=====================================
@@ -0,0 +1,9 @@
+#include <stdlib.h>
+
+const int * foo() {
+ int *x = malloc(sizeof(int));
+ *x = 42;
+ return x;
+}
+
+const int *bar = 0;
=====================================
testsuite/tests/ffi/should_compile/all.T
=====================================
@@ -43,3 +43,4 @@ test(
],
)
test('T15531', normal, compile, ['-Wall'])
+test('T22043', [omit_ways(['ghci'])], compile, [''])
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9a24241fb9ab508a58b1aae2203eadbbca201959
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9a24241fb9ab508a58b1aae2203eadbbca201959
You're receiving this email because of your account on gitlab.haskell.org.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-commits/attachments/20230123/8a2f5914/attachment-0001.html>
More information about the ghc-commits
mailing list