fatal error: bulkBarrierPreWrite: unaligned arguments [1.18 backport]

[randall77]

@randall77 requested issue #55122 to be considered for backport to the next 1.18 minor release.

Reproducer:

package main

func main() {
	for i := 0; i < 10000; i++ {
		h(i)
		sink = make([]byte, 1024) // generate some garbage
	}
}

func h(iter int) {
	var x [32]byte
	for i := 0; i < 32; i++ {
		x[i] = 99
	}
	g(&x)
	if x == ([32]byte{}) {
		return
	}
	for i := 0; i < 32; i++ {
		println(x[i])
	}
	panic(iter)
}

//go:noinline
func g(x interface{}) {
	switch e := x.(type) {
	case *[32]byte:
		var c [32]byte
		*e = c
	case *[]byte:
		*e = nil
	}
}

var sink []byte

[randall77]

This issue causes a rare but serious miscompilation.

[gopherbot]

Change https://go.dev/cl/431918 mentions this issue: [release-branch.go1.18] cmd/compile: avoid using destination pointer base type in memmove optimization

[gopherbot]

Closed by merging e0a364b to release-branch.go1.18.