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// Copyright 2009 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 ssagen
import (
"fmt"
"strings"
"cmd/compile/internal/base"
"cmd/compile/internal/ir"
"cmd/compile/internal/typecheck"
"cmd/compile/internal/types"
"cmd/internal/obj"
"cmd/internal/src"
)
func EnableNoWriteBarrierRecCheck() {
nowritebarrierrecCheck = newNowritebarrierrecChecker()
}
func NoWriteBarrierRecCheck() {
// Write barriers are now known. Check the
// call graph.
nowritebarrierrecCheck.check()
nowritebarrierrecCheck = nil
}
var nowritebarrierrecCheck *nowritebarrierrecChecker
type nowritebarrierrecChecker struct {
// extraCalls contains extra function calls that may not be
// visible during later analysis. It maps from the ODCLFUNC of
// the caller to a list of callees.
extraCalls map[*ir.Func][]nowritebarrierrecCall
// curfn is the current function during AST walks.
curfn *ir.Func
}
type nowritebarrierrecCall struct {
target *ir.Func // caller or callee
lineno src.XPos // line of call
}
// newNowritebarrierrecChecker creates a nowritebarrierrecChecker. It
// must be called before walk.
func newNowritebarrierrecChecker() *nowritebarrierrecChecker {
c := &nowritebarrierrecChecker{
extraCalls: make(map[*ir.Func][]nowritebarrierrecCall),
}
// Find all systemstack calls and record their targets. In
// general, flow analysis can't see into systemstack, but it's
// important to handle it for this check, so we model it
// directly. This has to happen before transforming closures in walk since
// it's a lot harder to work out the argument after.
for _, n := range typecheck.Target.Funcs {
c.curfn = n
if c.curfn.ABIWrapper() {
// We only want "real" calls to these
// functions, not the generated ones within
// their own ABI wrappers.
continue
}
ir.Visit(n, c.findExtraCalls)
}
c.curfn = nil
return c
}
func (c *nowritebarrierrecChecker) findExtraCalls(nn ir.Node) {
if nn.Op() != ir.OCALLFUNC {
return
}
n := nn.(*ir.CallExpr)
if n.Fun == nil || n.Fun.Op() != ir.ONAME {
return
}
fn := n.Fun.(*ir.Name)
if fn.Class != ir.PFUNC || fn.Defn == nil {
return
}
if types.RuntimeSymName(fn.Sym()) != "systemstack" {
return
}
var callee *ir.Func
arg := n.Args[0]
switch arg.Op() {
case ir.ONAME:
arg := arg.(*ir.Name)
callee = arg.Defn.(*ir.Func)
case ir.OCLOSURE:
arg := arg.(*ir.ClosureExpr)
callee = arg.Func
default:
base.Fatalf("expected ONAME or OCLOSURE node, got %+v", arg)
}
c.extraCalls[c.curfn] = append(c.extraCalls[c.curfn], nowritebarrierrecCall{callee, n.Pos()})
}
// recordCall records a call from ODCLFUNC node "from", to function
// symbol "to" at position pos.
//
// This should be done as late as possible during compilation to
// capture precise call graphs. The target of the call is an LSym
// because that's all we know after we start SSA.
//
// This can be called concurrently for different from Nodes.
func (c *nowritebarrierrecChecker) recordCall(fn *ir.Func, to *obj.LSym, pos src.XPos) {
// We record this information on the *Func so this is concurrent-safe.
if fn.NWBRCalls == nil {
fn.NWBRCalls = new([]ir.SymAndPos)
}
*fn.NWBRCalls = append(*fn.NWBRCalls, ir.SymAndPos{Sym: to, Pos: pos})
}
func (c *nowritebarrierrecChecker) check() {
// We walk the call graph as late as possible so we can
// capture all calls created by lowering, but this means we
// only get to see the obj.LSyms of calls. symToFunc lets us
// get back to the ODCLFUNCs.
symToFunc := make(map[*obj.LSym]*ir.Func)
// funcs records the back-edges of the BFS call graph walk. It
// maps from the ODCLFUNC of each function that must not have
// write barriers to the call that inhibits them. Functions
// that are directly marked go:nowritebarrierrec are in this
// map with a zero-valued nowritebarrierrecCall. This also
// acts as the set of marks for the BFS of the call graph.
funcs := make(map[*ir.Func]nowritebarrierrecCall)
// q is the queue of ODCLFUNC Nodes to visit in BFS order.
var q ir.NameQueue
for _, fn := range typecheck.Target.Funcs {
symToFunc[fn.LSym] = fn
// Make nowritebarrierrec functions BFS roots.
if fn.Pragma&ir.Nowritebarrierrec != 0 {
funcs[fn] = nowritebarrierrecCall{}
q.PushRight(fn.Nname)
}
// Check go:nowritebarrier functions.
if fn.Pragma&ir.Nowritebarrier != 0 && fn.WBPos.IsKnown() {
base.ErrorfAt(fn.WBPos, 0, "write barrier prohibited")
}
}
// Perform a BFS of the call graph from all
// go:nowritebarrierrec functions.
enqueue := func(src, target *ir.Func, pos src.XPos) {
if target.Pragma&ir.Yeswritebarrierrec != 0 {
// Don't flow into this function.
return
}
if _, ok := funcs[target]; ok {
// Already found a path to target.
return
}
// Record the path.
funcs[target] = nowritebarrierrecCall{target: src, lineno: pos}
q.PushRight(target.Nname)
}
for !q.Empty() {
fn := q.PopLeft().Func
// Check fn.
if fn.WBPos.IsKnown() {
var err strings.Builder
call := funcs[fn]
for call.target != nil {
fmt.Fprintf(&err, "\n\t%v: called by %v", base.FmtPos(call.lineno), call.target.Nname)
call = funcs[call.target]
}
base.ErrorfAt(fn.WBPos, 0, "write barrier prohibited by caller; %v%s", fn.Nname, err.String())
continue
}
// Enqueue fn's calls.
for _, callee := range c.extraCalls[fn] {
enqueue(fn, callee.target, callee.lineno)
}
if fn.NWBRCalls == nil {
continue
}
for _, callee := range *fn.NWBRCalls {
target := symToFunc[callee.Sym]
if target != nil {
enqueue(fn, target, callee.Pos)
}
}
}
}
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