libbacktrace/BacktracePtrace.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 <stdint.h>
#include <string.h>
#include <sys/uio.h>
#include <sys/param.h>
#include <sys/ptrace.h>
#include <sys/types.h>
#include <ucontext.h>
#include <unistd.h>

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

#include "BacktraceLog.h"
#include "BacktracePtrace.h"
#include "thread_utils.h"

#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), nullptr);
  if (*out_value == static_cast<word_t>(-1) && 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);

  struct iovec local_io;
  local_io.iov_base = buffer;
  local_io.iov_len = bytes;

  struct iovec remote_io;
  remote_io.iov_base = reinterpret_cast<void*>(addr);
  remote_io.iov_len = bytes;

  ssize_t bytes_read = process_vm_readv(Tid(), &local_io, 1, &remote_io, 1, 0);
  if (bytes_read == -1) {
    return 0;
  }
  return static_cast<size_t>(bytes_read);
#endif
}