unix: fix MremapPtr test failing on NetBSD

NetBSD apparently doesn't allow remapping into used address space. This means that the test that uses mremap to move a mmapped page into a new address should first mmap (to reserve) then munmap (to free) the destination. Fixes golang/go#68180 Change-Id: If66b67e7166ca4dc4331a8cfc3e3a285416e9849 GitHub-Last-Rev: 92058c2 GitHub-Pull-Request: #198 Cq-Include-Trybots: luci.golang.try:x_sys-gotip-netbsd-amd64 Reviewed-on: https://go-review.googlesource.com/c/sys/+/594756 Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Joedian Reid <joedian@google.com> Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: ncruces

unix/mremap_test.go

@@ -47,30 +47,31 @@ func TestMremap(t *testing.T) {
 }
 
 func TestMremapPtr(t *testing.T) {
-mmapProt := unix.PROT_NONE
-mmapPtrProt := unix.PROT_READ | unix.PROT_WRITE
-b, err := unix.Mmap(-1, 0, 2*unix.Getpagesize(), mmapProt, unix.MAP_ANON|unix.MAP_PRIVATE)
+p1, err := unix.MmapPtr(-1, 0, nil, uintptr(2*unix.Getpagesize()),
+unix.PROT_READ|unix.PROT_WRITE, unix.MAP_ANON|unix.MAP_PRIVATE)
 if err != nil {
-t.Fatalf("Mmap: %v", err)
-}
-if _, err := unix.MmapPtr(-1, 0, unsafe.Pointer(&b[0]), uintptr(unix.Getpagesize()),
-mmapPtrProt, unix.MAP_ANON|unix.MAP_PRIVATE|unix.MAP_FIXED); err != nil {
 t.Fatalf("MmapPtr: %v", err)
 }
 
-b[0] = 42
+p2 := unsafe.Add(p1, unix.Getpagesize())
+if err := unix.MunmapPtr(p2, uintptr(unix.Getpagesize())); err != nil {
+t.Fatalf("MunmapPtr: %v", err)
+}
+
+*(*byte)(p1) = 42
 
 if _, err := unix.MremapPtr(
-unsafe.Pointer(&b[0]), uintptr(unix.Getpagesize()),
-unsafe.Pointer(&b[unix.Getpagesize()]), uintptr(unix.Getpagesize()),
+p1, uintptr(unix.Getpagesize()),
+p2, uintptr(unix.Getpagesize()),
 unix.MremapFixed|unix.MremapMaymove); err != nil {
 t.Fatalf("MremapPtr: %v", err)
 }
-if got := b[unix.Getpagesize()]; got != 42 {
+
+if got := *(*byte)(p2); got != 42 {
 t.Errorf("got %d, want 42", got)
 }
 
-if err := unix.Munmap(b); err != nil {
-t.Fatalf("Munmap: %v", err)
+if err := unix.MunmapPtr(p2, uintptr(unix.Getpagesize())); err != nil {
+t.Fatalf("MunmapPtr: %v", err)
 }
 }