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The current go:nowritebarrierrec checker has two problems that limit its coverage: 1. It doesn't understand that systemstack calls its argument, which means there are several cases where we fail to detect prohibited write barriers. 2. It only observes calls in the AST, so calls constructed during lowering by SSA aren't followed. This CL completely rewrites this checker to address these issues. The current checker runs entirely after walk and uses visitBottomUp, which introduces several problems for checking across systemstack. First, visitBottomUp itself doesn't understand systemstack calls, so the callee may be ordered after the caller, causing the checker to fail to propagate constraints. Second, many systemstack calls are passed a closure, which is quite difficult to resolve back to the function definition after transformclosure and walk have run. Third, visitBottomUp works exclusively on the AST, so it can't observe calls created by SSA. To address these problems, this commit splits the check into two phases and rewrites it to use a call graph generated during SSA lowering. The first phase runs before transformclosure/walk and simply records systemstack arguments when they're easy to get. Then, it modifies genssa to record static call edges at the point where we're lowering to Progs (which is the latest point at which position information is conveniently available). Finally, the second phase runs after all functions have been lowered and uses a direct BFS walk of the call graph (combining systemstack calls with static calls) to find prohibited write barriers and construct nice error messages. Fixes #22384. For #22460. Change-Id: I39668f7f2366ab3c1ab1a71eaf25484d25349540 Reviewed-on: https://go-review.googlesource.com/72773 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
93 lines
1.2 KiB
Go
93 lines
1.2 KiB
Go
// errorcheck -+
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// Copyright 2016 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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// Test go:nowritebarrier and related directives.
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package p
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type t struct {
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f *t
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}
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var x t
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var y *t
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//go:nowritebarrier
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func a1() {
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x.f = y // ERROR "write barrier prohibited"
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a2() // no error
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}
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//go:noinline
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func a2() {
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x.f = y
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}
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//go:nowritebarrierrec
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func b1() {
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b2()
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}
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//go:noinline
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func b2() {
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x.f = y // ERROR "write barrier prohibited by caller"
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}
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// Test recursive cycles through nowritebarrierrec and yeswritebarrierrec.
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//go:nowritebarrierrec
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func c1() {
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c2()
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}
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//go:yeswritebarrierrec
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func c2() {
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c3()
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}
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func c3() {
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x.f = y
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c4()
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}
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//go:nowritebarrierrec
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func c4() {
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c2()
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}
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//go:nowritebarrierrec
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func d1() {
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d2()
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}
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func d2() {
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d3()
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}
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func d3() {
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x.f = y // ERROR "write barrier prohibited by caller"
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d4()
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}
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//go:yeswritebarrierrec
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func d4() {
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d2()
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}
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//go:noinline
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func systemstack(func()) {}
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//go:nowritebarrierrec
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func e1() {
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systemstack(e2)
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systemstack(func() {
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x.f = y // ERROR "write barrier prohibited by caller"
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})
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}
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func e2() {
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x.f = y // ERROR "write barrier prohibited by caller"
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}
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