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  	// Out of an abundance of caution, also make sure that there are
    21  	// no GCs actively in progress.
    22  	runtime.GC()
    23  
    24  	// Run badLR1 on its own stack to minimize the stack size and
    25  	// exercise the stack bounds logic in the hex dump.
    26  	go badLR1()
    27  	select {}
    28  }
    29  
    30  //go:noinline
    31  func badLR1() {
    32  	// We need two frames on LR machines because we'll smash this
    33  	// frame's saved LR.
    34  	badLR2(0)
    35  }
    36  
    37  //go:noinline
    38  func badLR2(arg int) {
    39  	// Smash the return PC or saved LR.
    40  	lrOff := unsafe.Sizeof(uintptr(0))
    41  	if runtime.GOARCH == "ppc64" || runtime.GOARCH == "ppc64le" {
    42  		lrOff = 32 // FIXED_FRAME or sys.MinFrameSize
    43  	}
    44  	lrPtr := (*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(&arg)) - lrOff))
    45  	*lrPtr = 0xbad
    46  
    47  	// Print a backtrace. This should include diagnostics for the
    48  	// bad return PC and a hex dump.
    49  	panic("backtrace")
    50  }
    51
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