runtime/debug: provide Addr method for errors from SetPanicOnFault

When we're building a panic that's triggered by a memory fault when
SetPanicOnFault has been called, include an Addr method. This
method reports the address at which the fault occurred.

Fixes #37023

RELNOTE=yes

Change-Id: Idff144587d6b75070fdc861a36efec76f4ec7384
Reviewed-on: https://go-review.googlesource.com/c/go/+/249677
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Keith Randall <khr@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/src/runtime/error.go b/src/runtime/error.go
index 386569bead..9e6cdf35dd 100644
--- a/src/runtime/error.go
+++ b/src/runtime/error.go
@@ -77,6 +77,26 @@ func (e errorString) Error() string {
 	return "runtime error: " + string(e)
 }
 
+type errorAddressString struct {
+	msg  string  // error message
+	addr uintptr // memory address where the error occurred
+}
+
+func (e errorAddressString) RuntimeError() {}
+
+func (e errorAddressString) Error() string {
+	return "runtime error: " + e.msg
+}
+
+// Addr returns the memory address where a fault occurred.
+// The address provided is best-effort.
+// The veracity of the result may depend on the platform.
+// Errors providing this method will only be returned as
+// a result of using runtime/debug.SetPanicOnFault.
+func (e errorAddressString) Addr() uintptr {
+	return e.addr
+}
+
 // plainError represents a runtime error described a string without
 // the prefix "runtime error: " after invoking errorString.Error().
 // See Issue #14965.