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