[RFC][PR 67336][PING^6] Verify pointers during stack unwind

[Yuri Gribov]

Hi all,

I've rebased the previous patch to trunk per Andrew's suggestion.
Original patch description/motivation/questions are in
https://gcc.gnu.org/ml/gcc-patches/2017-06/msg01869.html

-Y

safe-unwind-2.patch
Description: Binary data

#include <string.h>
#include <stdio.h>

struct _Unwind_Context;

typedef int (*_Unwind_Trace_Fn)(struct _Unwind_Context *, void *vdata);

extern int _Unwind_Backtrace(_Unwind_Trace_Fn trace, void * trace_argument);
extern int _Unwind_Backtrace_Checked(_Unwind_Trace_Fn trace, void * trace_argument);

#ifdef CHECK_UNWIND
#define _Unwind_Backtrace _Unwind_Backtrace_Checked
#endif

extern void *_Unwind_GetIP (struct _Unwind_Context *context);

int simple_unwind (struct _Unwind_Context *context, void *vdata) {
  printf("Next frame: ");
  void *pc = _Unwind_GetIP(context);
  printf("%p\n", pc);
  return 0;
}

#define noinline __attribute__((noinline))

noinline int foo() {
  // Clobber stack to provoke errors in unwinder
  int x;
  void *p = &x;
  asm("" :: "r"(p));
  memset(p, 0xa, 128);

  printf("After clobbering stack\n");

  int ret = _Unwind_Backtrace(simple_unwind, 0);
  printf("After unwind: %d\n", ret);
  printf("We're going to fail now\n");

  return 0;
}

noinline int bar() {
  int x = foo();
  return x + 1;
}

int main() {
  bar();
  return 0;
}