libbacktrace/BacktraceImpl.cpp

/*
 * Copyright (C) 2013 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 <errno.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <sys/ptrace.h>
#include <sys/types.h>
#include <ucontext.h>
#include <unistd.h>

#include <string>

#include <backtrace/Backtrace.h>
#include <backtrace/BacktraceMap.h>

#include "BacktraceImpl.h"
#include "BacktraceLog.h"
#include "thread_utils.h"

//-------------------------------------------------------------------------
// Backtrace functions.
//-------------------------------------------------------------------------
Backtrace::Backtrace(BacktraceImpl* impl, pid_t pid, BacktraceMap* map)
    : pid_(pid), tid_(-1), map_(map), map_shared_(true), impl_(impl) {
  impl_->SetParent(this);

  if (map_ == NULL) {
    map_ = BacktraceMap::Create(pid);
    map_shared_ = false;
  }
}

Backtrace::~Backtrace() {
  if (impl_) {
    delete impl_;
    impl_ = NULL;
  }

  if (map_ && !map_shared_) {
    delete map_;
    map_ = NULL;
  }
}

bool Backtrace::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
  return impl_->Unwind(num_ignore_frames, ucontext);
}

extern "C" char* __cxa_demangle(const char* mangled, char* buf, size_t* len,
                                int* status);

std::string Backtrace::GetFunctionName(uintptr_t pc, uintptr_t* offset) {
  std::string func_name = impl_->GetFunctionNameRaw(pc, offset);
  if (!func_name.empty()) {
#if defined(__APPLE__)
    // Mac OS' __cxa_demangle demangles "f" as "float"; last tested on 10.7.
    if (func_name[0] != '_') {
      return func_name;
    }
#endif
    char* name = __cxa_demangle(func_name.c_str(), 0, 0, 0);
    if (name) {
      func_name = name;
      free(name);
    }
  }
  return func_name;
}

bool Backtrace::VerifyReadWordArgs(uintptr_t ptr, word_t* out_value) {
  if (ptr & (sizeof(word_t)-1)) {
    BACK_LOGW("invalid pointer %p", (void*)ptr);
    *out_value = (word_t)-1;
    return false;
  }
  return true;
}

std::string Backtrace::FormatFrameData(size_t frame_num) {
  if (frame_num >= frames_.size()) {
    return "";
  }
  return FormatFrameData(&frames_[frame_num]);
}

std::string Backtrace::FormatFrameData(const backtrace_frame_data_t* frame) {
  const char* map_name;
  if (BacktraceMap::IsValid(frame->map) && !frame->map.name.empty()) {
    map_name = frame->map.name.c_str();
  } else {
    map_name = "<unknown>";
  }

  uintptr_t relative_pc;
  if (BacktraceMap::IsValid(frame->map)) {
    relative_pc = frame->pc - frame->map.start;
  } else {
    relative_pc = frame->pc;
  }

  char buf[512];
  if (!frame->func_name.empty() && frame->func_offset) {
    snprintf(buf, sizeof(buf), "#%02zu pc %0*" PRIxPTR "  %s (%s+%" PRIuPTR ")",
             frame->num, (int)sizeof(uintptr_t)*2, relative_pc, map_name,
             frame->func_name.c_str(), frame->func_offset);
  } else if (!frame->func_name.empty()) {
    snprintf(buf, sizeof(buf), "#%02zu pc %0*" PRIxPTR "  %s (%s)", frame->num,
             (int)sizeof(uintptr_t)*2, relative_pc, map_name, frame->func_name.c_str());
  } else {
    snprintf(buf, sizeof(buf), "#%02zu pc %0*" PRIxPTR "  %s", frame->num,
             (int)sizeof(uintptr_t)*2, relative_pc, map_name);
  }

  return buf;
}

void Backtrace::FillInMap(uintptr_t pc, backtrace_map_t* map) {
  map_->FillIn(pc, map);
}

//-------------------------------------------------------------------------
// BacktraceCurrent functions.
//-------------------------------------------------------------------------
BacktraceCurrent::BacktraceCurrent(
    BacktraceImpl* impl, BacktraceMap* map) : Backtrace(impl, getpid(), map) {
}

BacktraceCurrent::~BacktraceCurrent() {
}

bool BacktraceCurrent::ReadWord(uintptr_t ptr, word_t* out_value) {
  if (!VerifyReadWordArgs(ptr, out_value)) {
    return false;
  }

  backtrace_map_t map;
  FillInMap(ptr, &map);
  if (BacktraceMap::IsValid(map) && map.flags & PROT_READ) {
    *out_value = *reinterpret_cast<word_t*>(ptr);
    return true;
  } else {
    BACK_LOGW("pointer %p not in a readable map", reinterpret_cast<void*>(ptr));
    *out_value = static_cast<word_t>(-1);
    return false;
  }
}

size_t BacktraceCurrent::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
  backtrace_map_t map;
  FillInMap(addr, &map);
  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
    return 0;
  }
  bytes = MIN(map.end - addr, bytes);
  memcpy(buffer, reinterpret_cast<uint8_t*>(addr), bytes);
  return bytes;
}

//-------------------------------------------------------------------------
// BacktracePtrace functions.
//-------------------------------------------------------------------------
BacktracePtrace::BacktracePtrace(
    BacktraceImpl* impl, pid_t pid, pid_t tid, BacktraceMap* map)
    : Backtrace(impl, pid, map) {
  tid_ = tid;
}

BacktracePtrace::~BacktracePtrace() {
}

#if !defined(__APPLE__)
static bool PtraceRead(pid_t tid, uintptr_t addr, word_t* out_value) {
  // ptrace() returns -1 and sets errno when the operation fails.
  // To disambiguate -1 from a valid result, we clear errno beforehand.
  errno = 0;
  *out_value = ptrace(PTRACE_PEEKTEXT, tid, reinterpret_cast<void*>(addr), NULL);
  if (*out_value == static_cast<word_t>(-1) && errno) {
    BACK_LOGW("invalid pointer %p reading from tid %d, ptrace() strerror(errno)=%s",
              reinterpret_cast<void*>(addr), tid, strerror(errno));
    return false;
  }
  return true;
}
#endif

bool BacktracePtrace::ReadWord(uintptr_t ptr, word_t* out_value) {
#if defined(__APPLE__)
  BACK_LOGW("MacOS does not support reading from another pid.");
  return false;
#else
  if (!VerifyReadWordArgs(ptr, out_value)) {
    return false;
  }

  backtrace_map_t map;
  FillInMap(ptr, &map);
  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
    return false;
  }

  return PtraceRead(Tid(), ptr, out_value);
#endif
}

size_t BacktracePtrace::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
#if defined(__APPLE__)
  BACK_LOGW("MacOS does not support reading from another pid.");
  return 0;
#else
  backtrace_map_t map;
  FillInMap(addr, &map);
  if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
    return 0;
  }

  bytes = MIN(map.end - addr, bytes);
  size_t bytes_read = 0;
  word_t data_word;
  size_t align_bytes = addr & (sizeof(word_t) - 1);
  if (align_bytes != 0) {
    if (!PtraceRead(Tid(), addr & ~(sizeof(word_t) - 1), &data_word)) {
      return 0;
    }
    align_bytes = sizeof(word_t) - align_bytes;
    memcpy(buffer, reinterpret_cast<uint8_t*>(&data_word) + sizeof(word_t) - align_bytes,
           align_bytes);
    addr += align_bytes;
    buffer += align_bytes;
    bytes -= align_bytes;
    bytes_read += align_bytes;
  }

  size_t num_words = bytes / sizeof(word_t);
  for (size_t i = 0; i < num_words; i++) {
    if (!PtraceRead(Tid(), addr, &data_word)) {
      return bytes_read;
    }
    memcpy(buffer, &data_word, sizeof(word_t));
    buffer += sizeof(word_t);
    addr += sizeof(word_t);
    bytes_read += sizeof(word_t);
  }

  size_t left_over = bytes & (sizeof(word_t) - 1);
  if (left_over) {
    if (!PtraceRead(Tid(), addr, &data_word)) {
      return bytes_read;
    }
    memcpy(buffer, &data_word, left_over);
    bytes_read += left_over;
  }
  return bytes_read;
#endif
}

Backtrace* Backtrace::Create(pid_t pid, pid_t tid, BacktraceMap* map) {
  if (pid == BACKTRACE_CURRENT_PROCESS || pid == getpid()) {
    if (tid == BACKTRACE_CURRENT_THREAD || tid == gettid()) {
      return CreateCurrentObj(map);
    } else {
      return CreateThreadObj(tid, map);
    }
  } else if (tid == BACKTRACE_CURRENT_THREAD) {
    return CreatePtraceObj(pid, pid, map);
  } else {
    return CreatePtraceObj(pid, tid, map);
  }
}