runtime: clarify error when returning unpinned pointers

With the introduction of runtime.Pinner, returning a pointer to a pinned
struct that then points to an unpinned Go pointer is correctly caught.

However, the error message remained as "cgo result has Go pointer",
which should be updated to acknowledge that Go pointers to pinned
memory are allowed.

This also updates the comments for cgoCheckArg and cgoCheckResult
to similarly clarify.

Updates #46787

Change-Id: I147bb09e87dfb70a24d6d43e4cf84e8bcc2aff48
GitHub-Last-Rev: 706facb9f2bf28e1f6e575b7626f8feeca1187cf
GitHub-Pull-Request: golang/go#62606
Reviewed-on: https://go-review.googlesource.com/c/go/+/527702
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>

diff --git a/src/runtime/cgocall.go b/src/runtime/cgocall.go
index 73efd28491fe67231c15c1006961a09a1cb5fc03..6c2fd8f907a5f6cd48b45bf9b2a860a9fb0dbbf7 100644 (file)
--- a/src/runtime/cgocall.go
+++ b/src/runtime/cgocall.go
@@ -533,13 +533,13 @@ func cgoCheckPointer(ptr any, arg any) {
 }
 
 const cgoCheckPointerFail = "cgo argument has Go pointer to unpinned Go pointer"
-const cgoResultFail = "cgo result has Go pointer"
+const cgoResultFail = "cgo result is unpinned Go pointer or points to unpinned Go pointer"
 
 // cgoCheckArg is the real work of cgoCheckPointer. The argument p
 // is either a pointer to the value (of type t), or the value itself,
 // depending on indir. The top parameter is whether we are at the top
 // level, where Go pointers are allowed. Go pointers to pinned objects are
-// always allowed.
+// allowed as long as they don't reference other unpinned pointers.
 func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) {
        if t.PtrBytes == 0 || p == nil {
                // If the type has no pointers there is nothing to do.
@@ -726,8 +726,8 @@ func cgoInRange(p unsafe.Pointer, start, end uintptr) bool {
 }
 
 // cgoCheckResult is called to check the result parameter of an
-// exported Go function. It panics if the result is or contains a Go
-// pointer.
+// exported Go function. It panics if the result is or contains any
+// other pointer into unpinned Go memory.
 func cgoCheckResult(val any) {
        if !goexperiment.CgoCheck2 && debug.cgocheck == 0 {
                return