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//
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// notice, this list of conditions and the following disclaimer.
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// in the documentation and/or other materials provided with the
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Author: Arun Sharma
//
// Produce stack trace using libgcc

#include <unwind.h>  // ABI defined unwinder

#include <cstdlib>  // for nullptr

#include "stacktrace.h"

_START_GOOGLE_NAMESPACE_

struct trace_arg_t {
  void **result;
  int max_depth;
  int skip_count;
  int count;
};

// Workaround for the malloc() in _Unwind_Backtrace() issue.
static _Unwind_Reason_Code nop_backtrace(struct _Unwind_Context */*uc*/, void */*opq*/) {
  return _URC_NO_REASON;
}


// This code is not considered ready to run until
// static initializers run so that we are guaranteed
// that any malloc-related initialization is done.
static bool ready_to_run = false;
class StackTraceInit {
 public:
   StackTraceInit() {
     // Extra call to force initialization
     _Unwind_Backtrace(nop_backtrace, nullptr);
     ready_to_run = true;
   }
};

static StackTraceInit module_initializer;  // Force initialization

static _Unwind_Reason_Code GetOneFrame(struct _Unwind_Context *uc, void *opq) {
   auto *targ = static_cast<trace_arg_t *>(opq);

   if (targ->skip_count > 0) {
     targ->skip_count--;
   } else {
     targ->result[targ->count++] = reinterpret_cast<void *>(_Unwind_GetIP(uc));
   }

  if (targ->count == targ->max_depth) {
    return _URC_END_OF_STACK;
  }

  return _URC_NO_REASON;
}

// If you change this function, also change GetStackFrames below.
int GetStackTrace(void** result, int max_depth, int skip_count) {
  if (!ready_to_run) {
    return 0;
  }

  trace_arg_t targ;

  skip_count += 1;         // Do not include the "GetStackTrace" frame

  targ.result = result;
  targ.max_depth = max_depth;
  targ.skip_count = skip_count;
  targ.count = 0;

  _Unwind_Backtrace(GetOneFrame, &targ);

  return targ.count;
}

_END_GOOGLE_NAMESPACE_
