diff --git a/ui/build/path.go b/ui/build/path.go
new file mode 100644
index 0000000..52658ef
--- /dev/null
+++ b/ui/build/path.go
@@ -0,0 +1,149 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package build
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/google/blueprint/microfactory"
+
+	"android/soong/ui/build/paths"
+)
+
+func parsePathDir(dir string) []string {
+	f, err := os.Open(dir)
+	if err != nil {
+		return nil
+	}
+	defer f.Close()
+
+	if s, err := f.Stat(); err != nil || !s.IsDir() {
+		return nil
+	}
+
+	infos, err := f.Readdir(-1)
+	if err != nil {
+		return nil
+	}
+
+	ret := make([]string, 0, len(infos))
+	for _, info := range infos {
+		if m := info.Mode(); !m.IsDir() && m&0111 != 0 {
+			ret = append(ret, info.Name())
+		}
+	}
+	return ret
+}
+
+func SetupPath(ctx Context, config Config) {
+	if config.pathReplaced {
+		return
+	}
+
+	ctx.BeginTrace("path")
+	defer ctx.EndTrace()
+
+	origPath, _ := config.Environment().Get("PATH")
+	myPath := filepath.Join(config.OutDir(), ".path")
+	interposer := myPath + "_interposer"
+
+	var cfg microfactory.Config
+	cfg.Map("android/soong", "build/soong")
+	cfg.TrimPath, _ = filepath.Abs(".")
+	if _, err := microfactory.Build(&cfg, interposer, "android/soong/cmd/path_interposer"); err != nil {
+		ctx.Fatalln("Failed to build path interposer:", err)
+	}
+
+	if err := ioutil.WriteFile(interposer+"_origpath", []byte(origPath), 0777); err != nil {
+		ctx.Fatalln("Failed to write original path:", err)
+	}
+
+	entries, err := paths.LogListener(ctx.Context, interposer+"_log")
+	if err != nil {
+		ctx.Fatalln("Failed to listen for path logs:", err)
+	}
+
+	go func() {
+		for log := range entries {
+			curPid := os.Getpid()
+			for i, proc := range log.Parents {
+				if proc.Pid == curPid {
+					log.Parents = log.Parents[i:]
+					break
+				}
+			}
+			procPrints := []string{
+				"See https://android.googlesource.com/platform/build/+/master/Changes.md#PATH_Tools for more information.",
+			}
+			if len(log.Parents) > 0 {
+				procPrints = append(procPrints, "Process tree:")
+				for i, proc := range log.Parents {
+					procPrints = append(procPrints, fmt.Sprintf("%s→ %s", strings.Repeat(" ", i), proc.Command))
+				}
+			}
+
+			config := paths.GetConfig(log.Basename)
+			if config.Error {
+				ctx.Printf("Disallowed PATH tool %q used: %#v", log.Basename, log.Args)
+				for _, line := range procPrints {
+					ctx.Println(line)
+				}
+			} else {
+				ctx.Verbosef("Unknown PATH tool %q used: %#v", log.Basename, log.Args)
+				for _, line := range procPrints {
+					ctx.Verboseln(line)
+				}
+			}
+		}
+	}()
+
+	ensureEmptyDirectoriesExist(ctx, myPath)
+
+	var execs []string
+	for _, pathEntry := range filepath.SplitList(origPath) {
+		if pathEntry == "" {
+			// Ignore the current directory
+			continue
+		}
+		// TODO(dwillemsen): remove path entries under TOP? or anything
+		// that looks like an android source dir? They won't exist on
+		// the build servers, since they're added by envsetup.sh.
+		// (Except for the JDK, which is configured in ui/build/config.go)
+
+		execs = append(execs, parsePathDir(pathEntry)...)
+	}
+
+	allowAllSymlinks := config.Environment().IsEnvTrue("TEMPORARY_DISABLE_PATH_RESTRICTIONS")
+	for _, name := range execs {
+		if !paths.GetConfig(name).Symlink && !allowAllSymlinks {
+			continue
+		}
+
+		err := os.Symlink("../.path_interposer", filepath.Join(myPath, name))
+		// Intentionally ignore existing files -- that means that we
+		// just created it, and the first one should win.
+		if err != nil && !os.IsExist(err) {
+			ctx.Fatalln("Failed to create symlink:", err)
+		}
+	}
+
+	myPath, _ = filepath.Abs(myPath)
+	config.Environment().Set("PATH", myPath)
+	config.pathReplaced = true
+}