//go:build !sqlite3_nosys package alloc import ( "math" "reflect" "unsafe" "github.com/tetratelabs/wazero/experimental" "golang.org/x/sys/windows" ) func Virtual(_, max uint64) experimental.LinearMemory { // Round up to the page size. rnd := uint64(windows.Getpagesize() - 1) max = (max + rnd) &^ rnd if max > math.MaxInt { // This ensures uintptr(max) overflows to a large value, // and windows.VirtualAlloc returns an error. max = math.MaxUint64 } // Reserve max bytes of address space, to ensure we won't need to move it. // This does not commit memory. r, err := windows.VirtualAlloc(0, uintptr(max), windows.MEM_RESERVE, windows.PAGE_READWRITE) if err != nil { panic(err) } mem := virtualMemory{addr: r} // SliceHeader, although deprecated, avoids a go vet warning. sh := (*reflect.SliceHeader)(unsafe.Pointer(&mem.buf)) sh.Cap = int(max) sh.Data = r return &mem } // The slice covers the entire mmapped memory: // - len(buf) is the already committed memory, // - cap(buf) is the reserved address space. type virtualMemory struct { buf []byte addr uintptr } func (m *virtualMemory) 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(windows.Getpagesize() - 1) new := (size + rnd) &^ rnd // Commit additional memory up to new bytes. _, err := windows.VirtualAlloc(m.addr, uintptr(new), windows.MEM_COMMIT, windows.PAGE_READWRITE) 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 *virtualMemory) Free() { err := windows.VirtualFree(m.addr, 0, windows.MEM_RELEASE) if err != nil { panic(err) } m.addr = 0 }