libgo/go/runtime/testdata/testprog/badtraceback.go

   1 // Copyright 2018 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package main
   6
   7 import (
   8         "runtime"
   9         "runtime/debug"
  10         "unsafe"
  11 )
  12
  13 func init() {
  14         register("BadTraceback", BadTraceback)
  15 }
  16
  17 func BadTraceback() {
  18         // Disable GC to prevent traceback at unexpected time.
  19         debug.SetGCPercent(-1)
  20
  21         // Run badLR1 on its own stack to minimize the stack size and
  22         // exercise the stack bounds logic in the hex dump.
  23         go badLR1()
  24         select {}
  25 }
  26
  27 //go:noinline
  28 func badLR1() {
  29         // We need two frames on LR machines because we'll smash this
  30         // frame's saved LR.
  31         badLR2(0)
  32 }
  33
  34 //go:noinline
  35 func badLR2(arg int) {
  36         // Smash the return PC or saved LR.
  37         lrOff := unsafe.Sizeof(uintptr(0))
  38         if runtime.GOARCH == "ppc64" || runtime.GOARCH == "ppc64le" {
  39                 lrOff = 32 // FIXED_FRAME or sys.MinFrameSize
  40         }
  41         lrPtr := (*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(&arg)) - lrOff))
  42         *lrPtr = 0xbad
  43
  44         // Print a backtrace. This should include diagnostics for the
  45         // bad return PC and a hex dump.
  46         panic("backtrace")
  47 }