package main

import (
    "math/rand"
    "runtime"
)

func main() {
    P := 2 * runtime.GOMAXPROCS(0)
    ptrs := make([][]*int, P)
    for i := 0; i < P; i++ {
        i := i
        go func() {
            r := rand.New(rand.NewSource(int64(i)))
            var sink []byte
            p := make([]*int, 4)
            z := make([]*int, 4)
            ptrs[i] = p
            for {
                if r.Intn(20) != 0 {
                    a := p[:1]
                    a[0] = new(int)
                    for j := range a {
                        a[j] = nil
                    }
                    for j := range p {
                        p[j] = new(int)
                    }
                    copy(p[:3], z)
                    for j := range p {
                        p[j] = new(int)
                    }
                    copy(p[1:4], z)
                    for j := range p {
                        p[j] = new(int)
                        copy(p[j:j+1], z)
                    }
                } else {
                    sink = make([]byte, 8<<10)
                }
            }
            _ = sink
        }()
    }
    select {}
}

GODEBUG=invalidptr=1 GOARCH=386 go run memclr.go

runtime: pointer 0x18d90000 to unallocated spanidx=0x548 span.start=0x185d2000 span.limit=0x185d4000 span.state=3
runtime: found in object at *(0x18456000+0x0)
object=0x18456000 k=0xc22b s.start*_PageSize=0x18456000 s.limit=0x18458000 s.sizeclass=2 s.elemsize=16
 *(object+0) = 0x0 <==
 *(object+4) = 0x0
 *(object+8) = 0x18d9b354
 *(object+12) = 0x18d9b3b0
fatal error: found bad pointer in Go heap (incorrect use of unsafe or cgo?)

_3or4:
    MOVW    AX, (DI)
    MOVW    AX, -2(DI)(BX*1)

TEXT runtime·memclr(SB),NOSPLIT,$0-8
    MOVL    ptr+0(FP), DI
    MOVL    n+4(FP), CX
    MOVQ    CX, BX
    ANDQ    $3, BX
    SHRQ    $2, CX
    MOVQ    $0, AX
    CLD
    REP
    STOSL
    MOVQ    BX, CX
    REP
    STOSB
    RET

move_3or4:
    MOVW    (SI), AX
    MOVW    -2(SI)(BX*1), CX
    MOVW    AX, (DI)
    MOVW    CX, -2(DI)(BX*1)
    RET

_1or2:
    MOVB    AX, (DI)
    MOVB    AX, -1(DI)(BX*1)

_5through8:
    MOVL    AX, (DI)
    MOVL    AX, -4(DI)(BX*1)