From 52d5cb2822966c00ce2ef97eb08bec4850d76fb2 Mon Sep 17 00:00:00 2001
From: Cherry Zhang <cherryyz@google.com>
Date: Wed, 3 Feb 2021 18:10:04 -0500
Subject: [PATCH] [dev.regabi] cmd/internal/obj: access Attribute atomically

Symbol's Attributes and ABI are in the same word. In the
concurrent backend, we may read one symbol's ABI (the callee)
while setting its attributes in another goroutine.

Fix racecompile build.

Change-Id: I500e869bafdd72080119ab243db94eee3afcf926
Reviewed-on: https://go-review.googlesource.com/c/go/+/289290
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
---
 src/cmd/internal/obj/link.go | 64 ++++++++++++++++++++++--------------
 1 file changed, 40 insertions(+), 24 deletions(-)

diff --git a/src/cmd/internal/obj/link.go b/src/cmd/internal/obj/link.go
index 35cb53cbf6..8206902328 100644
--- a/src/cmd/internal/obj/link.go
+++ b/src/cmd/internal/obj/link.go
@@ -39,6 +39,7 @@ import (
 	"cmd/internal/sys"
 	"fmt"
 	"sync"
+	"sync/atomic"
 )
 
 // An Addr is an argument to an instruction.
@@ -647,37 +648,52 @@ const (
 	attrABIBase
 )
 
-func (a Attribute) DuplicateOK() bool        { return a&AttrDuplicateOK != 0 }
-func (a Attribute) MakeTypelink() bool       { return a&AttrMakeTypelink != 0 }
-func (a Attribute) CFunc() bool              { return a&AttrCFunc != 0 }
-func (a Attribute) NoSplit() bool            { return a&AttrNoSplit != 0 }
-func (a Attribute) Leaf() bool               { return a&AttrLeaf != 0 }
-func (a Attribute) OnList() bool             { return a&AttrOnList != 0 }
-func (a Attribute) ReflectMethod() bool      { return a&AttrReflectMethod != 0 }
-func (a Attribute) Local() bool              { return a&AttrLocal != 0 }
-func (a Attribute) Wrapper() bool            { return a&AttrWrapper != 0 }
-func (a Attribute) NeedCtxt() bool           { return a&AttrNeedCtxt != 0 }
-func (a Attribute) NoFrame() bool            { return a&AttrNoFrame != 0 }
-func (a Attribute) Static() bool             { return a&AttrStatic != 0 }
-func (a Attribute) WasInlined() bool         { return a&AttrWasInlined != 0 }
-func (a Attribute) TopFrame() bool           { return a&AttrTopFrame != 0 }
-func (a Attribute) Indexed() bool            { return a&AttrIndexed != 0 }
-func (a Attribute) UsedInIface() bool        { return a&AttrUsedInIface != 0 }
-func (a Attribute) ContentAddressable() bool { return a&AttrContentAddressable != 0 }
-func (a Attribute) ABIWrapper() bool         { return a&AttrABIWrapper != 0 }
+func (a *Attribute) load() Attribute { return Attribute(atomic.LoadUint32((*uint32)(a))) }
+
+func (a *Attribute) DuplicateOK() bool        { return a.load()&AttrDuplicateOK != 0 }
+func (a *Attribute) MakeTypelink() bool       { return a.load()&AttrMakeTypelink != 0 }
+func (a *Attribute) CFunc() bool              { return a.load()&AttrCFunc != 0 }
+func (a *Attribute) NoSplit() bool            { return a.load()&AttrNoSplit != 0 }
+func (a *Attribute) Leaf() bool               { return a.load()&AttrLeaf != 0 }
+func (a *Attribute) OnList() bool             { return a.load()&AttrOnList != 0 }
+func (a *Attribute) ReflectMethod() bool      { return a.load()&AttrReflectMethod != 0 }
+func (a *Attribute) Local() bool              { return a.load()&AttrLocal != 0 }
+func (a *Attribute) Wrapper() bool            { return a.load()&AttrWrapper != 0 }
+func (a *Attribute) NeedCtxt() bool           { return a.load()&AttrNeedCtxt != 0 }
+func (a *Attribute) NoFrame() bool            { return a.load()&AttrNoFrame != 0 }
+func (a *Attribute) Static() bool             { return a.load()&AttrStatic != 0 }
+func (a *Attribute) WasInlined() bool         { return a.load()&AttrWasInlined != 0 }
+func (a *Attribute) TopFrame() bool           { return a.load()&AttrTopFrame != 0 }
+func (a *Attribute) Indexed() bool            { return a.load()&AttrIndexed != 0 }
+func (a *Attribute) UsedInIface() bool        { return a.load()&AttrUsedInIface != 0 }
+func (a *Attribute) ContentAddressable() bool { return a.load()&AttrContentAddressable != 0 }
+func (a *Attribute) ABIWrapper() bool         { return a.load()&AttrABIWrapper != 0 }
 
 func (a *Attribute) Set(flag Attribute, value bool) {
-	if value {
-		*a |= flag
-	} else {
-		*a &^= flag
+	for {
+		v0 := a.load()
+		v := v0
+		if value {
+			v |= flag
+		} else {
+			v &^= flag
+		}
+		if atomic.CompareAndSwapUint32((*uint32)(a), uint32(v0), uint32(v)) {
+			break
+		}
 	}
 }
 
-func (a Attribute) ABI() ABI { return ABI(a / attrABIBase) }
+func (a *Attribute) ABI() ABI { return ABI(a.load() / attrABIBase) }
 func (a *Attribute) SetABI(abi ABI) {
 	const mask = 1 // Only one ABI bit for now.
-	*a = (*a &^ (mask * attrABIBase)) | Attribute(abi)*attrABIBase
+	for {
+		v0 := a.load()
+		v := (v0 &^ (mask * attrABIBase)) | Attribute(abi)*attrABIBase
+		if atomic.CompareAndSwapUint32((*uint32)(a), uint32(v0), uint32(v)) {
+			break
+		}
+	}
 }
 
 var textAttrStrings = [...]struct {
-- 
2.50.0