Adding upstream version 1.11.0+dfsg.

Signed-off-by: Daniel Baumann <daniel@debian.org>

mmap_unix.go

@@ -0,0 +1,70 @@
+// Copyright 2011 Evan Shaw. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE-MMAP-GO file.
+
+//go:build unix
+
+// Modifications (c) 2017 The Memory Authors.
+
+package memory // import "modernc.org/memory"
+
+import (
+	"golang.org/x/sys/unix"
+	"os"
+	"unsafe"
+)
+
+const pageSizeLog = 16
+
+var (
+	osPageMask = osPageSize - 1
+	osPageSize = os.Getpagesize()
+)
+
+func unmap(addr uintptr, size int) error {
+	return unix.MunmapPtr(unsafe.Pointer(addr), uintptr(size))
+}
+
+// pageSize aligned.
+func mmap(size int) (uintptr, int, error) {
+	size = roundup(size, osPageSize)
+	// Ask for more so we can align the result at a pageSize boundary
+	n := size + pageSize
+	up, err := unix.MmapPtr(-1, 0, nil, uintptr(n), unix.PROT_READ|unix.PROT_WRITE, unix.MAP_PRIVATE|unix.MAP_ANON)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	p := uintptr(up)
+	if p&uintptr(osPageMask) != 0 {
+		panic("internal error")
+	}
+
+	mod := int(p) & pageMask
+	if mod != 0 { // Return the extra part before pageSize aligned block
+		m := pageSize - mod
+		if err := unmap(p, m); err != nil {
+			unmap(p, n) // Do not leak the first mmap
+			return 0, 0, err
+		}
+
+		n -= m
+		p += uintptr(m)
+	}
+
+	if p&uintptr(pageMask) != 0 {
+		panic("internal error")
+	}
+
+	if n > size { // Return the extra part after pageSize aligned block
+		if err := unmap(p+uintptr(size), n-size); err != nil {
+			// Do not error when the kernel rejects the extra part after, just return the
+			// unexpectedly enlarged size.
+			//
+			// Fixes the bigsort.test failures on linux/s390x, see: https://gitlab.com/cznic/sqlite/-/issues/207
+			size = n
+		}
+	}
+
+	return p, size, nil
+}