3 files changed, 62 insertions, 3 deletions
diff --git a/libgo/go/runtime/debug/garbage.go b/libgo/go/runtime/debug/garbage.go
index 785e9d4..00f92c3 100644
--- a/libgo/go/runtime/debug/garbage.go
+++ b/libgo/go/runtime/debug/garbage.go
@@ -106,6 +106,8 @@ func FreeOSMemory() {
 // the program crashes.
 // SetMaxStack returns the previous setting.
 // The initial setting is 1 GB on 64-bit systems, 250 MB on 32-bit systems.
+// There may be a system-imposed maximum stack limit regardless
+// of the value provided to SetMaxStack.
 //
 // SetMaxStack is useful mainly for limiting the damage done by
 // goroutines that enter an infinite recursion. It only limits future
@@ -139,6 +141,11 @@ func SetMaxThreads(threads int) int {
 // manipulation of memory may cause faults at non-nil addresses in less
 // dramatic situations; SetPanicOnFault allows such programs to request
 // that the runtime trigger only a panic, not a crash.
+// The runtime.Error that the runtime panics with may have an additional method:
+//     Addr() uintptr
+// If that method exists, it returns the memory address which triggered the fault.
+// The results of Addr are best-effort and the veracity of the result
+// may depend on the platform.
 // SetPanicOnFault applies only to the current goroutine.
 // It returns the previous setting.
 func SetPanicOnFault(enabled bool) bool {
diff --git a/libgo/go/runtime/debug/heapdump_test.go b/libgo/go/runtime/debug/heapdump_test.go
index de1ec27..768934d 100644
--- a/libgo/go/runtime/debug/heapdump_test.go
+++ b/libgo/go/runtime/debug/heapdump_test.go
@@ -5,7 +5,6 @@
 package debug_test
 
 import (
-	"io/ioutil"
 	"os"
 	"runtime"
 	. "runtime/debug"
@@ -16,7 +15,7 @@ func TestWriteHeapDumpNonempty(t *testing.T) {
 	if runtime.GOOS == "js" {
 		t.Skipf("WriteHeapDump is not available on %s.", runtime.GOOS)
 	}
-	f, err := ioutil.TempFile("", "heapdumptest")
+	f, err := os.CreateTemp("", "heapdumptest")
 	if err != nil {
 		t.Fatalf("TempFile failed: %v", err)
 	}
@@ -45,7 +44,7 @@ func TestWriteHeapDumpFinalizers(t *testing.T) {
 	if runtime.GOOS == "js" {
 		t.Skipf("WriteHeapDump is not available on %s.", runtime.GOOS)
 	}
-	f, err := ioutil.TempFile("", "heapdumptest")
+	f, err := os.CreateTemp("", "heapdumptest")
 	if err != nil {
 		t.Fatalf("TempFile failed: %v", err)
 	}
diff --git a/libgo/go/runtime/debug/panic_test.go b/libgo/go/runtime/debug/panic_test.go
new file mode 100644
index 0000000..b67a3de
--- /dev/null
+++ b/libgo/go/runtime/debug/panic_test.go
@@ -0,0 +1,53 @@
+// Copyright 2020 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.
+
+// +build aix darwin dragonfly freebsd linux netbsd openbsd
+
+// TODO: test on Windows?
+
+package debug_test
+
+import (
+	"runtime"
+	"runtime/debug"
+	"syscall"
+	"testing"
+	"unsafe"
+)
+
+func TestPanicOnFault(t *testing.T) {
+	if runtime.GOARCH == "s390x" {
+		t.Skip("s390x fault addresses are missing the low order bits")
+	}
+	if runtime.GOOS == "ios" {
+		t.Skip("iOS doesn't provide fault addresses")
+	}
+	m, err := syscall.Mmap(-1, 0, 0x1000, syscall.PROT_READ /* Note: no PROT_WRITE */, syscall.MAP_SHARED|syscall.MAP_ANON)
+	if err != nil {
+		t.Fatalf("can't map anonymous memory: %s", err)
+	}
+	defer syscall.Munmap(m)
+	old := debug.SetPanicOnFault(true)
+	defer debug.SetPanicOnFault(old)
+	const lowBits = 0x3e7
+	defer func() {
+		r := recover()
+		if r == nil {
+			t.Fatalf("write did not fault")
+		}
+		type addressable interface {
+			Addr() uintptr
+		}
+		a, ok := r.(addressable)
+		if !ok {
+			t.Fatalf("fault does not contain address")
+		}
+		want := uintptr(unsafe.Pointer(&m[lowBits]))
+		got := a.Addr()
+		if got != want {
+			t.Fatalf("fault address %x, want %x", got, want)
+		}
+	}()
+	m[lowBits] = 1 // will fault
+}