mirror of
https://github.com/golang/go
synced 2024-11-23 05:20:11 -07:00
42b023d7b9
They can't reasonably be allocated on the heap. Not a huge deal, but it has an interesting and useful side effect. After CL 249917, the compiler and runtime treat pointers to go:notinheap types as uintptrs instead of real pointers (no write barrier, not processed during stack scanning, ...). That feature is exactly what we want for cgo to fix #40954. All the cases we have of pointers declared in C, but which might actually be filled with non-pointer data, are of this form (JNI's jobject heirarch, Darwin's CFType heirarchy, ...). Fixes #40954 Change-Id: I44a3b9bc2513d4287107e39d0cbbd0efd46a3aae Reviewed-on: https://go-review.googlesource.com/c/go/+/250940 Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com> TryBot-Result: Go Bot <gobot@golang.org> Trust: Keith Randall <khr@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>
36 lines
840 B
Go
36 lines
840 B
Go
// run
|
|
|
|
// Copyright 2020 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package main
|
|
|
|
import (
|
|
"unsafe"
|
|
)
|
|
|
|
//go:notinheap
|
|
type S struct{ x int }
|
|
|
|
func main() {
|
|
var i int
|
|
p := (*S)(unsafe.Pointer(uintptr(unsafe.Pointer(&i))))
|
|
v := uintptr(unsafe.Pointer(p))
|
|
// p is a pointer to a go:notinheap type. Like some C libraries,
|
|
// we stored an integer in that pointer. That integer just happens
|
|
// to be the address of i.
|
|
// v is also the address of i.
|
|
// p has a base type which is marked go:notinheap, so it
|
|
// should not be adjusted when the stack is copied.
|
|
recurse(100, p, v)
|
|
}
|
|
func recurse(n int, p *S, v uintptr) {
|
|
if n > 0 {
|
|
recurse(n-1, p, v)
|
|
}
|
|
if uintptr(unsafe.Pointer(p)) != v {
|
|
panic("adjusted notinheap pointer")
|
|
}
|
|
}
|