path: root/src/cmd/compile/internal/gc/dcl.go

// 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 gc

import (
	"bytes"
	"cmd/compile/internal/base"
	"cmd/compile/internal/ir"
	"cmd/compile/internal/typecheck"
	"cmd/compile/internal/types"
	"cmd/internal/obj"
	"cmd/internal/src"
	"fmt"
)

func EnableNoWriteBarrierRecCheck() {
	nowritebarrierrecCheck = newNowritebarrierrecChecker()
}

func NoWriteBarrierRecCheck() {
	// Write barriers are now known. Check the
	// call graph.
	nowritebarrierrecCheck.check()
	nowritebarrierrecCheck = nil
}

var nowritebarrierrecCheck *nowritebarrierrecChecker

// oldname returns the Node that declares symbol s in the current scope.
// If no such Node currently exists, an ONONAME Node is returned instead.
// Automatically creates a new closure variable if the referenced symbol was
// declared in a different (containing) function.
func oldname(s *types.Sym) ir.Node {
	if s.Pkg != types.LocalPkg {
		return ir.NewIdent(base.Pos, s)
	}

	n := ir.AsNode(s.Def)
	if n == nil {
		// Maybe a top-level declaration will come along later to
		// define s. resolve will check s.Def again once all input
		// source has been processed.
		return ir.NewIdent(base.Pos, s)
	}

	if ir.CurFunc != nil && n.Op() == ir.ONAME && n.Name().Curfn != nil && n.Name().Curfn != ir.CurFunc {
		// Inner func is referring to var in outer func.
		//
		// TODO(rsc): If there is an outer variable x and we
		// are parsing x := 5 inside the closure, until we get to
		// the := it looks like a reference to the outer x so we'll
		// make x a closure variable unnecessarily.
		n := n.(*ir.Name)
		c := n.Name().Innermost
		if c == nil || c.Curfn != ir.CurFunc {
			// Do not have a closure var for the active closure yet; make one.
			c = typecheck.NewName(s)
			c.Class_ = ir.PAUTOHEAP
			c.SetIsClosureVar(true)
			c.SetIsDDD(n.IsDDD())
			c.Defn = n

			// Link into list of active closure variables.
			// Popped from list in func funcLit.
			c.Outer = n.Name().Innermost
			n.Name().Innermost = c

			ir.CurFunc.ClosureVars = append(ir.CurFunc.ClosureVars, c)
		}

		// return ref to closure var, not original
		return c
	}

	return n
}

// importName is like oldname,
// but it reports an error if sym is from another package and not exported.
func importName(sym *types.Sym) ir.Node {
	n := oldname(sym)
	if !types.IsExported(sym.Name) && sym.Pkg != types.LocalPkg {
		n.SetDiag(true)
		base.Errorf("cannot refer to unexported name %s.%s", sym.Pkg.Name, sym.Name)
	}
	return n
}

func fakeRecv() *ir.Field {
	return ir.NewField(base.Pos, nil, nil, types.FakeRecvType())
}

// funcsym returns s·f.
func funcsym(s *types.Sym) *types.Sym {
	// funcsymsmu here serves to protect not just mutations of funcsyms (below),
	// but also the package lookup of the func sym name,
	// since this function gets called concurrently from the backend.
	// There are no other concurrent package lookups in the backend,
	// except for the types package, which is protected separately.
	// Reusing funcsymsmu to also cover this package lookup
	// avoids a general, broader, expensive package lookup mutex.
	// Note makefuncsym also does package look-up of func sym names,
	// but that it is only called serially, from the front end.
	funcsymsmu.Lock()
	sf, existed := s.Pkg.LookupOK(ir.FuncSymName(s))
	// Don't export s·f when compiling for dynamic linking.
	// When dynamically linking, the necessary function
	// symbols will be created explicitly with makefuncsym.
	// See the makefuncsym comment for details.
	if !base.Ctxt.Flag_dynlink && !existed {
		funcsyms = append(funcsyms, s)
	}
	funcsymsmu.Unlock()
	return sf
}

// makefuncsym ensures that s·f is exported.
// It is only used with -dynlink.
// When not compiling for dynamic linking,
// the funcsyms are created as needed by
// the packages that use them.
// Normally we emit the s·f stubs as DUPOK syms,
// but DUPOK doesn't work across shared library boundaries.
// So instead, when dynamic linking, we only create
// the s·f stubs in s's package.
func makefuncsym(s *types.Sym) {
	if !base.Ctxt.Flag_dynlink {
		base.Fatalf("makefuncsym dynlink")
	}
	if s.IsBlank() {
		return
	}
	if base.Flag.CompilingRuntime && (s.Name == "getg" || s.Name == "getclosureptr" || s.Name == "getcallerpc" || s.Name == "getcallersp") {
		// runtime.getg(), getclosureptr(), getcallerpc(), and
		// getcallersp() are not real functions and so do not
		// get funcsyms.
		return
	}
	if _, existed := s.Pkg.LookupOK(ir.FuncSymName(s)); !existed {
		funcsyms = append(funcsyms, s)
	}
}

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 transformclosure and 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 transformclosure since
	// it's a lot harder to work out the argument after.
	for _, n := range typecheck.Target.Decls {
		if n.Op() != ir.ODCLFUNC {
			continue
		}
		c.curfn = n.(*ir.Func)
		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.X == nil || n.X.Op() != ir.ONAME {
		return
	}
	fn := n.X.(*ir.Name)
	if fn.Class_ != ir.PFUNC || fn.Name().Defn == nil {
		return
	}
	if !types.IsRuntimePkg(fn.Sym().Pkg) || fn.Sym().Name != "systemstack" {
		return
	}

	var callee *ir.Func
	arg := n.Args[0]
	switch arg.Op() {
	case ir.ONAME:
		arg := arg.(*ir.Name)
		callee = arg.Name().Defn.(*ir.Func)
	case ir.OCLOSURE:
		arg := arg.(*ir.ClosureExpr)
		callee = arg.Func
	default:
		base.Fatalf("expected ONAME or OCLOSURE node, got %+v", arg)
	}
	if callee.Op() != ir.ODCLFUNC {
		base.Fatalf("expected ODCLFUNC node, got %+v", callee)
	}
	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 _, n := range typecheck.Target.Decls {
		if n.Op() != ir.ODCLFUNC {
			continue
		}
		fn := n.(*ir.Func)

		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, "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 bytes.Buffer
			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, "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)
			}
		}
	}
}