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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.
// Modifications (c) 2022 The Memory Authors.
package memory // import "modernc.org/memory"
import (
"os"
"syscall"
_ "unsafe"
)
const (
pageSizeLog = 20
// $ find /usr/include -name syscall.h
// /usr/include/sys/syscall.h
// $ grep -ni munmap /usr/include/sys/syscall.h
// 293:#define SYS_munmap 117
// $ grep -ni mmap /usr/include/sys/syscall.h
// 291:#define SYS_mmap 115
// 303:#define SYS_mmapobj 127
// 442:#define SYS_mmap64 214
// $
// $ uname -a
// SunOS omnios64 5.11 omnios-r151044-d3b715b9d1 i86pc i386 i86pc
// $
sys_MUNMAP = 117
sys_MMAP = 214
)
var (
osPageMask = osPageSize - 1
osPageSize = os.Getpagesize()
)
//go:linkname mmapSyscall syscall.mmap
func mmapSyscall(addr uintptr, length uintptr, prot int, flags int, fd int, offset int64) (xaddr uintptr, err error)
func unmap(addr uintptr, size int) error {
_, _, errno := 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
}
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