source: code/trunk/vendor/modernc.org/memory/mmap_unix.go@ 822

// 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 darwin || dragonfly || freebsd || linux || openbsd || (solaris && !illumos) || netbsd
// +build darwin dragonfly freebsd linux openbsd solaris,!illumos netbsd

// Modifications (c) 2017 The Memory Authors.

package memory // import "modernc.org/memory"

import (
        "os"
        "syscall"
)

const pageSizeLog = 20

var (
        osPageMask = osPageSize - 1
        osPageSize = os.Getpagesize()
)

func unmap(addr uintptr, size int) error {
        _, _, errno := syscall.Syscall(syscall.SYS_MUNMAP, addr, uintptr(size), 0)
        if errno != 0 {
                return errno
        }

        return nil
}

// pageSize aligned.
func mmap(size int) (uintptr, int, error) {
        size = roundup(size, osPageSize)
        // The actual mmap syscall varies by architecture. mmapSyscall provides same
        // functionality as the unexported funtion syscall.mmap and is declared in
        // mmap_*_*.go and mmap_fallback.go. To add support for a new architecture,
        // check function mmap in src/syscall/syscall_*_*.go or
        // src/syscall/zsyscall_*_*.go in Go's source code.
        p, err := mmapSyscall(0, uintptr(size+pageSize), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_PRIVATE|syscall.MAP_ANON, -1, 0)
        if err != nil {
                return 0, 0, err
        }

        n := size + pageSize
        if p&uintptr(osPageMask) != 0 {
                panic("internal error")
        }

        mod := int(p) & pageMask
        if mod != 0 {
                m := pageSize - mod
                if err := unmap(p, m); err != nil {
                        return 0, 0, err
                }

                n -= m
                p += uintptr(m)
        }

        if p&uintptr(pageMask) != 0 {
                panic("internal error")
        }

        if n-size != 0 {
                if err := unmap(p+uintptr(size), n-size); err != nil {
                        return 0, 0, err
                }
        }

        return p, size, nil
}