72 lines
1.7 KiB
Go
72 lines
1.7 KiB
Go
//go:build unix
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package util
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import (
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"math"
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"github.com/tetratelabs/wazero/experimental"
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"golang.org/x/sys/unix"
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)
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func mmappedAllocator(cap, max uint64) experimental.LinearMemory {
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// Round up to the page size.
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rnd := uint64(unix.Getpagesize() - 1)
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max = (max + rnd) &^ rnd
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cap = (cap + rnd) &^ rnd
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if max > math.MaxInt {
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// This ensures int(max) overflows to a negative value,
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// and unix.Mmap returns EINVAL.
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max = math.MaxUint64
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}
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// Reserve max bytes of address space, to ensure we won't need to move it.
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// A protected, private, anonymous mapping should not commit memory.
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b, err := unix.Mmap(-1, 0, int(max), unix.PROT_NONE, unix.MAP_PRIVATE|unix.MAP_ANON)
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if err != nil {
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panic(err)
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}
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// Commit the initial cap bytes of memory.
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err = unix.Mprotect(b[:cap], unix.PROT_READ|unix.PROT_WRITE)
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if err != nil {
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unix.Munmap(b)
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panic(err)
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}
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return &mmappedMemory{buf: b[:cap]}
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}
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// The slice covers the entire mmapped memory:
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// - len(buf) is the already committed memory,
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// - cap(buf) is the reserved address space.
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type mmappedMemory struct {
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buf []byte
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}
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func (m *mmappedMemory) Reallocate(size uint64) []byte {
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if com := uint64(len(m.buf)); com < size {
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// Round up to the page size.
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rnd := uint64(unix.Getpagesize() - 1)
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new := (size + rnd) &^ rnd
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// Commit additional memory up to new bytes.
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err := unix.Mprotect(m.buf[com:new], unix.PROT_READ|unix.PROT_WRITE)
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if err != nil {
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panic(err)
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}
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// Update committed memory.
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m.buf = m.buf[:new]
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}
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// Limit returned capacity because bytes beyond
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// len(m.buf) have not yet been committed.
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return m.buf[:size:len(m.buf)]
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}
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func (m *mmappedMemory) Free() {
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err := unix.Munmap(m.buf[:cap(m.buf)])
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if err != nil {
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panic(err)
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}
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m.buf = nil
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}
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