105 lines
2.3 KiB
Go
105 lines
2.3 KiB
Go
package json
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import (
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"fmt"
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"reflect"
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"sync/atomic"
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"unsafe"
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)
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const (
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maxAcceptableTypeAddrRange = 1024 * 1024 * 2 // 2 Mib
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)
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var (
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cachedDecoder []decoder
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cachedDecoderMap unsafe.Pointer // map[uintptr]decoder
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baseTypeAddr uintptr
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maxTypeAddr uintptr
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typeAddrShift uintptr
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)
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//go:linkname typelinks reflect.typelinks
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func typelinks() ([]unsafe.Pointer, [][]int32)
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//go:linkname rtypeOff reflect.rtypeOff
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func rtypeOff(unsafe.Pointer, int32) unsafe.Pointer
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func setupCodec() error {
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sections, offsets := typelinks()
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if len(sections) != 1 {
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return fmt.Errorf("failed to get sections")
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}
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if len(offsets) != 1 {
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return fmt.Errorf("failed to get offsets")
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}
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section := sections[0]
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offset := offsets[0]
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var (
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min uintptr = uintptr(^uint(0))
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max uintptr = 0
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isAligned64 = true
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isAligned32 = true
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)
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for i := 0; i < len(offset); i++ {
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typ := (*rtype)(rtypeOff(section, offset[i]))
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addr := uintptr(unsafe.Pointer(typ))
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if min > addr {
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min = addr
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}
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if max < addr {
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max = addr
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}
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if typ.Kind() == reflect.Ptr {
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addr = uintptr(unsafe.Pointer(typ.Elem()))
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if min > addr {
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min = addr
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}
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if max < addr {
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max = addr
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}
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}
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// check every address is aligned from the base address
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isAligned64 = isAligned64 && (addr-min)&63 == 0
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isAligned32 = isAligned32 && (addr-min)&31 == 0
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}
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addrRange := max - min
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if addrRange == 0 {
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return fmt.Errorf("failed to get address range of types")
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}
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if isAligned64 {
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typeAddrShift = 6
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} else if isAligned32 {
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typeAddrShift = 5
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}
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cacheSize := addrRange >> typeAddrShift
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if cacheSize > maxAcceptableTypeAddrRange {
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return fmt.Errorf("too big address range %d", addrRange)
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}
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cachedDecoder = make([]decoder, cacheSize)
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baseTypeAddr = min
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maxTypeAddr = max
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return nil
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}
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func init() {
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_ = setupCodec()
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}
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func loadDecoderMap() map[uintptr]decoder {
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p := atomic.LoadPointer(&cachedDecoderMap)
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return *(*map[uintptr]decoder)(unsafe.Pointer(&p))
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}
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func storeDecoder(typ uintptr, dec decoder, m map[uintptr]decoder) {
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newDecoderMap := make(map[uintptr]decoder, len(m)+1)
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newDecoderMap[typ] = dec
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for k, v := range m {
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newDecoderMap[k] = v
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}
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atomic.StorePointer(&cachedDecoderMap, *(*unsafe.Pointer)(unsafe.Pointer(&newDecoderMap)))
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}
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