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//go:build unix && !sqlite3_nosys
package alloc
import (
"math"
"github.com/tetratelabs/wazero/experimental"
"golang.org/x/sys/unix"
)
func Virtual(_, max uint64) experimental.LinearMemory {
// Round up to the page size.
rnd := uint64(unix.Getpagesize() - 1)
max = (max + rnd) &^ rnd
if max > math.MaxInt {
// This ensures int(max) overflows to a negative value,
// and unix.Mmap returns EINVAL.
max = math.MaxUint64
}
// Reserve max bytes of address space, to ensure we won't need to move it.
// A protected, private, anonymous mapping should not commit memory.
b, err := unix.Mmap(-1, 0, int(max), unix.PROT_NONE, unix.MAP_PRIVATE|unix.MAP_ANON)
if err != nil {
panic(err)
}
return &mmappedMemory{buf: b[:0]}
}
// The slice covers the entire mmapped memory:
// - len(buf) is the already committed memory,
// - cap(buf) is the reserved address space.
type mmappedMemory struct {
buf []byte
}
func (m *mmappedMemory) Reallocate(size uint64) []byte {
com := uint64(len(m.buf))
res := uint64(cap(m.buf))
if com < size && size <= res {
// Round up to the page size.
rnd := uint64(unix.Getpagesize() - 1)
new := (size + rnd) &^ rnd
// Commit additional memory up to new bytes.
err := unix.Mprotect(m.buf[com:new], unix.PROT_READ|unix.PROT_WRITE)
if err != nil {
panic(err)
}
// Update committed memory.
m.buf = m.buf[:new]
}
// Limit returned capacity because bytes beyond
// len(m.buf) have not yet been committed.
return m.buf[:size:len(m.buf)]
}
func (m *mmappedMemory) Free() {
err := unix.Munmap(m.buf[:cap(m.buf)])
if err != nil {
panic(err)
}
m.buf = nil
}
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