[Git][ghc/ghc][wip/T22043] CApiFFI: add ConstPtr for encoding const-qualified pointer return types (#22043)
Alex D (@nineonine)
gitlab at gitlab.haskell.org
Fri Nov 11 22:22:33 UTC 2022
Alex D pushed to branch wip/T22043 at Glasgow Haskell Compiler / GHC
Commits:
4f70a8a0 by nineonine at 2022-11-11T14:22:24-08:00
CApiFFI: add ConstPtr for encoding const-qualified pointer return types (#22043)
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
- - - - -
9 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/Foreign/C/Types.hs
- + testsuite/tests/ffi/should_compile/T22034.h
- + testsuite/tests/ffi/should_compile/T22034.hs
- + testsuite/tests/ffi/should_compile/T22034_c.c
- testsuite/tests/ffi/should_compile/all.T
Changes:
=====================================
compiler/GHC/Builtin/Names.hs
=====================================
@@ -346,7 +346,7 @@ 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,
@@ -553,7 +553,7 @@ 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_TYPES :: Module
gHC_PRIM = mkPrimModule (fsLit "GHC.Prim") -- Primitive types and values
gHC_PRIM_PANIC = mkPrimModule (fsLit "GHC.Prim.Panic")
@@ -623,6 +623,7 @@ 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_TYPES = mkBaseModule (fsLit "Foreign.C.Types")
gHC_SRCLOC :: Module
gHC_SRCLOC = mkBaseModule (fsLit "GHC.SrcLoc")
@@ -1656,6 +1657,10 @@ fingerprintDataConName :: Name
fingerprintDataConName =
dcQual gHC_FINGERPRINT_TYPE (fsLit "Fingerprint") fingerprintDataConKey
+constPtrConName :: Name
+constPtrConName =
+ tcQual fOREIGN_C_TYPES (fsLit "ConstPtr") constPtrTyConKey
+
{-
************************************************************************
* *
@@ -1852,7 +1857,7 @@ statePrimTyConKey, stableNamePrimTyConKey, stableNameTyConKey,
funPtrTyConKey, tVarPrimTyConKey, eqPrimTyConKey,
eqReprPrimTyConKey, eqPhantPrimTyConKey,
compactPrimTyConKey, stackSnapshotPrimTyConKey,
- promptTagPrimTyConKey :: Unique
+ promptTagPrimTyConKey, constPtrTyConKey :: Unique
statePrimTyConKey = mkPreludeTyConUnique 50
stableNamePrimTyConKey = mkPreludeTyConUnique 51
stableNameTyConKey = mkPreludeTyConUnique 52
@@ -2059,6 +2064,7 @@ 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 (#22034)
+ | (_, res_ty1) <- tcSplitFunTys ty1
+ , newty <- maybe res_ty1 snd (tcSplitIOType_maybe res_ty1)
+ , Just (ptr, _) <- splitTyConApp_maybe newty
+ , tyConName ptr `elem` [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
=====================================
@@ -157,6 +157,9 @@ 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.Types` 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/Foreign/C/Types.hs
=====================================
@@ -84,8 +84,11 @@ 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 )
@@ -214,6 +217,9 @@ 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
@@ -259,4 +265,3 @@ representing a C type @t@:
corresponding bitwise operation in C on @t at .
-}
-
=====================================
testsuite/tests/ffi/should_compile/T22034.h
=====================================
@@ -0,0 +1,2 @@
+const int *foo();
+const double *bar;
=====================================
testsuite/tests/ffi/should_compile/T22034.hs
=====================================
@@ -0,0 +1,10 @@
+{-# LANGUAGE CApiFFI #-}
+module T22034 where
+
+import Foreign.C.Types
+
+foreign import capi "T22034.h foo"
+ c_foo :: IO (ConstPtr CInt)
+
+foreign import capi "T22034.h value bar"
+ c_bar :: ConstPtr CDouble
=====================================
testsuite/tests/ffi/should_compile/T22034_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('T22034', [omit_ways(['ghci'])], compile, [''])
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/4f70a8a0b5db49ff249271faefec14bf1421f365
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/4f70a8a0b5db49ff249271faefec14bf1421f365
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