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|
package runtime
import (
"reflect"
"sync"
"unsafe"
)
type SliceHeader struct {
Data unsafe.Pointer
Len int
Cap int
}
const (
maxAcceptableTypeAddrRange = 1024 * 1024 * 2 // 2 Mib
)
type TypeAddr struct {
BaseTypeAddr uintptr
MaxTypeAddr uintptr
AddrRange uintptr
AddrShift uintptr
}
var (
typeAddr *TypeAddr
once sync.Once
)
//go:linkname typelinks reflect.typelinks
func typelinks() ([]unsafe.Pointer, [][]int32)
//go:linkname rtypeOff reflect.rtypeOff
func rtypeOff(unsafe.Pointer, int32) unsafe.Pointer
func AnalyzeTypeAddr() *TypeAddr {
once.Do(func() {
sections, offsets := typelinks()
if len(sections) != 1 {
return
}
if len(offsets) != 1 {
return
}
section := sections[0]
offset := offsets[0]
var (
min uintptr = uintptr(^uint(0))
max uintptr = 0
isAligned64 = true
isAligned32 = true
)
for i := 0; i < len(offset); i++ {
typ := (*Type)(rtypeOff(section, offset[i]))
addr := uintptr(unsafe.Pointer(typ))
if min > addr {
min = addr
}
if max < addr {
max = addr
}
if typ.Kind() == reflect.Ptr {
addr = uintptr(unsafe.Pointer(typ.Elem()))
if min > addr {
min = addr
}
if max < addr {
max = addr
}
}
isAligned64 = isAligned64 && (addr-min)&63 == 0
isAligned32 = isAligned32 && (addr-min)&31 == 0
}
addrRange := max - min
if addrRange == 0 {
return
}
var addrShift uintptr
if isAligned64 {
addrShift = 6
} else if isAligned32 {
addrShift = 5
}
cacheSize := addrRange >> addrShift
if cacheSize > maxAcceptableTypeAddrRange {
return
}
typeAddr = &TypeAddr{
BaseTypeAddr: min,
MaxTypeAddr: max,
AddrRange: addrRange,
AddrShift: addrShift,
}
})
return typeAddr
}
|
