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// 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
}
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