/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <cxxabi.h>
#include <dlfcn.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <unwind.h>

#if defined(NDEBUG)
#error This translation unit should not be used in release builds
#endif

namespace {

constexpr size_t kDemangledNameLen = 4096;

bool g_sighandler_registered = false;
char* g_demangled_name = nullptr;

struct SigHandler {
  int sig_num;
  struct sigaction old_handler;
};

SigHandler g_signals[] = {{SIGSEGV}, {SIGILL}, {SIGTRAP},
                          {SIGABRT}, {SIGBUS}, {SIGFPE}};

template <typename T>
void Print(const T& str) {
  write(STDERR_FILENO, str, sizeof(str));
}

template <typename T>
void PrintHex(T n) {
  for (unsigned i = 0; i < sizeof(n) * 8; i += 4) {
    char nibble = static_cast<char>(n >> (sizeof(n) * 8 - i - 4)) & 0x0F;
    char c = (nibble < 10) ? '0' + nibble : 'A' + nibble - 10;
    write(STDERR_FILENO, &c, 1);
  }
}

struct StackCrawlState {
  StackCrawlState(uintptr_t* frames_arg, size_t max_depth_arg)
      : frames(frames_arg),
        frame_count(0),
        max_depth(max_depth_arg),
        skip_count(1) {}

  uintptr_t* frames;
  size_t frame_count;
  size_t max_depth;
  size_t skip_count;
};

_Unwind_Reason_Code TraceStackFrame(_Unwind_Context* context, void* arg) {
  StackCrawlState* state = static_cast<StackCrawlState*>(arg);
  uintptr_t ip = _Unwind_GetIP(context);

  if (ip != 0 && state->skip_count) {
    state->skip_count--;
    return _URC_NO_REASON;
  }

  state->frames[state->frame_count++] = ip;
  if (state->frame_count >= state->max_depth)
    return _URC_END_OF_STACK;
  return _URC_NO_REASON;
}

// Note: use only async-safe functions inside this.
void SignalHandler(int sig_num, siginfo_t* info, void* ucontext) {
  // Restore the old handlers.
  for (size_t i = 0; i < sizeof(g_signals) / sizeof(g_signals[0]); i++)
    sigaction(g_signals[i].sig_num, &g_signals[i].old_handler, nullptr);

  Print("\n------------------ BEGINNING OF CRASH ------------------\n");
  Print("Signal: ");
  if (sig_num == SIGSEGV) {
    Print("Segmentation fault");
  } else if (sig_num == SIGILL) {
    Print("Illegal instruction (possibly unaligned access)");
  } else if (sig_num == SIGTRAP) {
    Print("Trap");
  } else if (sig_num == SIGABRT) {
    Print("Abort");
  } else if (sig_num == SIGBUS) {
    Print("Bus Error (possibly unmapped memory access)");
  } else if (sig_num == SIGFPE) {
    Print("Floating point exception");
  } else {
    Print("Unexpected signal ");
    PrintHex(static_cast<uint32_t>(sig_num));
  }

  Print("\n");

  Print("Fault addr: ");
  PrintHex(reinterpret_cast<uintptr_t>(info->si_addr));
  Print("\n\nBacktrace:\n");

  const size_t kMaxFrames = 32;
  uintptr_t frames[kMaxFrames];
  StackCrawlState unwind_state(frames, kMaxFrames);
  _Unwind_Backtrace(&TraceStackFrame, &unwind_state);

  for (uint8_t i = 0; i < unwind_state.frame_count; i++) {
    Dl_info sym_info = {};
    int res = dladdr(reinterpret_cast<void*>(frames[i]), &sym_info);
    Print("\n#");
    PrintHex(i);
    Print("  ");
    if (res) {
      const char* sym_name = sym_info.dli_sname;
      int ignored;
      size_t len = kDemangledNameLen;
      char* demangled = abi::__cxa_demangle(sym_info.dli_sname,
                                            g_demangled_name, &len, &ignored);
      if (demangled) {
        sym_name = demangled;
        // In the exceptional case of demangling something > kDemangledNameLen,
        // __cxa_demangle will realloc(). In that case the malloc()-ed pointer
        // might be moved.
        g_demangled_name = demangled;
      }
      write(STDERR_FILENO, sym_name, strlen(sym_name));
    } else {
      Print("???");
    }
    Print("\n");
  }

  Print("------------------ END OF CRASH ------------------\n");
}

// __attribute__((constructor)) causes a static initializer that automagically
// early runs this function before the main().
void __attribute__((constructor)) EnableStacktraceOnCrashForDebug();

void EnableStacktraceOnCrashForDebug() {
  if (g_sighandler_registered)
    return;
  g_sighandler_registered = true;

  // Pre-allocate the string for __cxa_demangle() to reduce the risk of that
  // invoking realloc() within the signal handler.
  g_demangled_name = reinterpret_cast<char*>(malloc(kDemangledNameLen));
  struct sigaction sigact;
  sigact.sa_sigaction = &SignalHandler;
  sigact.sa_flags = static_cast<decltype(sigact.sa_flags)>(
      SA_RESTART | SA_SIGINFO | SA_RESETHAND);
  for (size_t i = 0; i < sizeof(g_signals) / sizeof(g_signals[0]); i++)
    sigaction(g_signals[i].sig_num, &sigact, &g_signals[i].old_handler);
}

}  // namespace