cmd/cgo: rewrite CFTypeRef and subytes on Darwin to uintptr

Cgo currently maps CFTypeRef and its subtypes to unsafe.Pointer
or a pointer to a named empty struct.

However, Darwin sometimes encodes some of CFTypeRef's subtypes as a
few int fields packed in a pointer wrapper. This hackery confuses the
Go runtime as the pointers can look like they point to things that
shouldn't be pointed at.

Switch CFTypeRef and its subtypes to map to uintptr.

Detecting the affected set of types is tricky, there are over 200 of
them, and the set isn't static across Darwin versions. Fortunately,
downcasting from CFTypeRef to a subtype requires calling CFGetTypeID,
getting a CFTypeID token, and comparing that with a known id from a
*GetTypeID() call. So we can find all the type names by detecting all
the *GetTypeID() prototypes and rewriting the corresponding *Ref types
to uintptr. This strategy covers all the cases I've checked and is
unlikely to have a false positive.

Update #23091.

Change-Id: I487eb4105c9b4785ba564de9c38d472c8c9a76ac
Reviewed-on: https://go-review.googlesource.com/87615
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/cmd/fix/cftype.go b/src/cmd/fix/cftype.go
index 1f06cd6c33..841bd4dccb 100644
--- a/src/cmd/fix/cftype.go
+++ b/src/cmd/fix/cftype.go
@@ -19,7 +19,7 @@ var cftypeFix = fix{
 	name:     "cftype",
 	date:     "2017-09-27",
 	f:        cftypefix,
-	desc:     `Fixes initializers of C.CF*Ptr types`,
+	desc:     `Fixes initializers of C.*Ref types`,
 	disabled: false,
 }
 
@@ -27,11 +27,11 @@ var cftypeFix = fix{
 //   type CFTypeRef unsafe.Pointer
 // New state:
 //   type CFTypeRef uintptr
-// and similar for other CF*Ref types.
+// and similar for other *Ref types.
 // This fix finds nils initializing these types and replaces the nils with 0s.
 func cftypefix(f *ast.File) bool {
 	return typefix(f, func(s string) bool {
-		return strings.HasPrefix(s, "C.CF") && strings.HasSuffix(s, "Ref")
+		return strings.HasPrefix(s, "C.") && strings.HasSuffix(s, "Ref")
 	})
 }