runtime: fix line number for faulting instructions

Unlike function calls, when processing instructions that directly
fault we must not subtract 1 from the pc before looking up the
file/line information.

Since the file/line lookup unconditionally subtracts 1, add 1 to
the faulting instruction PCs to compensate.

Fixes #34123

Change-Id: Ie7361e3d2f84a0d4f48d97e5a9e74f6291ba7a8b
Reviewed-on: https://go-review.googlesource.com/c/go/+/196962
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

test/fixedbugs/issue34123.go

@@ -0,0 +1,43 @@
+// run
+
+// Copyright 2019 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.
+
+// Make sure that the line number is reported correctly
+// for faulting instructions.
+
+package main
+
+import (
+	"fmt"
+	"runtime"
+)
+
+var x byte
+var p *byte
+
+//go:noinline
+func f() {
+	q := p
+	x = 11  // line 23
+	*q = 12 // line 24
+}
+func main() {
+	defer func() {
+		recover()
+		var pcs [10]uintptr
+		n := runtime.Callers(1, pcs[:])
+		frames := runtime.CallersFrames(pcs[:n])
+		for {
+			f, more := frames.Next()
+			if f.Function == "main.f" && f.Line != 24 {
+				panic(fmt.Errorf("expected line 24, got line %d", f.Line))
+			}
+			if !more {
+				break
+			}
+		}
+	}()
+	f()
+}