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// +build go1.21
/*
* Copyright 2021 ByteDance Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package rt
import (
`sync/atomic`
`unsafe`
`golang.org/x/arch/x86/x86asm`
)
//go:linkname GcWriteBarrier2 runtime.gcWriteBarrier2
func GcWriteBarrier2()
//go:linkname RuntimeWriteBarrier runtime.writeBarrier
var RuntimeWriteBarrier uintptr
const (
_MaxInstr = 15
)
func isvar(arg x86asm.Arg) bool {
v, ok := arg.(x86asm.Mem)
return ok && v.Base == x86asm.RIP
}
func iszero(arg x86asm.Arg) bool {
v, ok := arg.(x86asm.Imm)
return ok && v == 0
}
func GcwbAddr() uintptr {
var err error
var off uintptr
var ins x86asm.Inst
/* get the function address */
pc := uintptr(0)
fp := FuncAddr(atomic.StorePointer)
/* search within the first 16 instructions */
for i := 0; i < 16; i++ {
mem := unsafe.Pointer(uintptr(fp) + pc)
buf := BytesFrom(mem, _MaxInstr, _MaxInstr)
/* disassemble the instruction */
if ins, err = x86asm.Decode(buf, 64); err != nil {
panic("gcwbaddr: " + err.Error())
}
/* check for a byte comparison with zero */
if ins.Op == x86asm.CMP && ins.MemBytes == 1 && isvar(ins.Args[0]) && iszero(ins.Args[1]) {
off = pc + uintptr(ins.Len) + uintptr(ins.Args[0].(x86asm.Mem).Disp)
break
}
/* move to next instruction */
nb := ins.Len
pc += uintptr(nb)
}
/* check for address */
if off == 0 {
panic("gcwbaddr: could not locate the variable `writeBarrier`")
} else {
return uintptr(fp) + off
}
}
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