92 lines
2.1 KiB
Go
92 lines
2.1 KiB
Go
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// 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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// Modifications (c) 2022 The Memory Authors.
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package memory // import "modernc.org/memory"
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import (
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"os"
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"syscall"
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_ "unsafe"
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)
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const (
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pageSizeLog = 20
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// $ find /usr/include -name syscall.h
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// /usr/include/sys/syscall.h
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// $ grep -ni munmap /usr/include/sys/syscall.h
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// 293:#define SYS_munmap 117
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// $ grep -ni mmap /usr/include/sys/syscall.h
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// 291:#define SYS_mmap 115
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// 303:#define SYS_mmapobj 127
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// 442:#define SYS_mmap64 214
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// $
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// $ uname -a
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// SunOS omnios64 5.11 omnios-r151044-d3b715b9d1 i86pc i386 i86pc
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// $
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sys_MUNMAP = 117
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sys_MMAP = 214
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)
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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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//go:linkname mmapSyscall syscall.mmap
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func mmapSyscall(addr uintptr, length uintptr, prot int, flags int, fd int, offset int64) (xaddr uintptr, err error)
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func unmap(addr uintptr, size int) error {
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_, _, errno := syscall.Syscall(sys_MUNMAP, addr, uintptr(size), 0)
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if errno != 0 {
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return errno
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}
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return nil
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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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// The actual mmap syscall varies by architecture. mmapSyscall provides same
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// functionality as the unexported funtion syscall.mmap and is declared in
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// mmap_*_*.go and mmap_fallback.go. To add support for a new architecture,
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// check function mmap in src/syscall/syscall_*_*.go or
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// src/syscall/zsyscall_*_*.go in Go's source code.
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p, err := mmapSyscall(0, uintptr(size+pageSize), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_PRIVATE|syscall.MAP_ANON, -1, 0)
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if err != nil {
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return 0, 0, err
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}
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n := size + pageSize
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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 {
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m := pageSize - mod
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if err := unmap(p, m); err != nil {
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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 != 0 {
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if err := unmap(p+uintptr(size), n-size); err != nil {
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return 0, 0, err
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}
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}
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return p, size, nil
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}
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