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https://github.com/golang/go
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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
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// Copyright 2020 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import (
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"unsafe"
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)
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//go:notinheap
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type S struct{ x int }
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func main() {
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var i int
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p := (*S)(unsafe.Pointer(uintptr(unsafe.Pointer(&i))))
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v := uintptr(unsafe.Pointer(p))
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// p is a pointer to a go:notinheap type. Like some C libraries,
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// we stored an integer in that pointer. That integer just happens
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// to be the address of i.
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// v is also the address of i.
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// p has a base type which is marked go:notinheap, so it
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// should not be adjusted when the stack is copied.
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recurse(100, p, v)
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}
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func recurse(n int, p *S, v uintptr) {
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if n > 0 {
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recurse(n-1, p, v)
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}
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if uintptr(unsafe.Pointer(p)) != v {
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panic("adjusted notinheap pointer")
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}
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}
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