upload android base code part6

android/system/core/libmemunreachable/PtracerThread.cpp

@@ -0,0 +1,154 @@
+/*
+ * Copyright (C) 2016 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 <fcntl.h>
+#include <inttypes.h>
+#include <pthread.h>
+#include <sched.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "android-base/macros.h"
+
+#include "PtracerThread.h"
+#include "anon_vma_naming.h"
+#include "log.h"
+
+namespace android {
+
+class Stack {
+ public:
+  explicit Stack(size_t size) : size_(size) {
+    int prot = PROT_READ | PROT_WRITE;
+    int flags = MAP_PRIVATE | MAP_ANONYMOUS;
+    page_size_ = sysconf(_SC_PAGE_SIZE);
+    size_ += page_size_ * 2;  // guard pages
+    base_ = mmap(NULL, size_, prot, flags, -1, 0);
+    if (base_ == MAP_FAILED) {
+      base_ = NULL;
+      size_ = 0;
+      return;
+    }
+    prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, base_, size_, "libmemunreachable stack");
+    mprotect(base_, page_size_, PROT_NONE);
+    mprotect(top(), page_size_, PROT_NONE);
+  };
+  ~Stack() { munmap(base_, size_); };
+  void* top() {
+    return reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(base_) + size_ - page_size_);
+  };
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(Stack);
+
+  void* base_;
+  size_t size_;
+  size_t page_size_;
+};
+
+PtracerThread::PtracerThread(const std::function<int()>& func) : child_pid_(0) {
+  stack_ = std::make_unique<Stack>(PTHREAD_STACK_MIN);
+  if (stack_->top() == nullptr) {
+    MEM_LOG_ALWAYS_FATAL("failed to mmap child stack: %s", strerror(errno));
+  }
+
+  func_ = std::function<int()>{[&, func]() -> int {
+    // In the child thread, lock and unlock the mutex to wait for the parent
+    // to finish setting up for the child thread
+    std::unique_lock<std::mutex> lk(m_);
+    lk.unlock();
+    _exit(func());
+  }};
+}
+
+PtracerThread::~PtracerThread() {
+  Kill();
+  Join();
+  ClearTracer();
+  stack_ = nullptr;
+}
+
+bool PtracerThread::Start() {
+  std::unique_lock<std::mutex> lk(m_);
+
+  // Convert from void(*)(void*) to lambda with captures
+  auto proxy = [](void* arg) -> int {
+    prctl(PR_SET_NAME, "libmemunreachable ptrace thread");
+    return (*reinterpret_cast<std::function<int()>*>(arg))();
+  };
+
+  child_pid_ = clone(proxy, stack_->top(), CLONE_VM | CLONE_FS | CLONE_FILES /*|CLONE_UNTRACED*/,
+                     reinterpret_cast<void*>(&func_));
+  if (child_pid_ < 0) {
+    MEM_ALOGE("failed to clone child: %s", strerror(errno));
+    return false;
+  }
+
+  SetTracer(child_pid_);
+
+  lk.unlock();
+
+  return true;
+}
+
+int PtracerThread::Join() {
+  if (child_pid_ == -1) {
+    return -1;
+  }
+  int status;
+  int ret = TEMP_FAILURE_RETRY(waitpid(child_pid_, &status, __WALL));
+  if (ret < 0) {
+    MEM_ALOGE("waitpid %d failed: %s", child_pid_, strerror(errno));
+    return -1;
+  }
+
+  child_pid_ = -1;
+
+  if (WIFEXITED(status)) {
+    return WEXITSTATUS(status);
+  } else if (WIFSIGNALED(status)) {
+    return -WTERMSIG(status);
+  } else {
+    MEM_ALOGE("unexpected status %x", status);
+    return -1;
+  }
+}
+
+void PtracerThread::Kill() {
+  if (child_pid_ == -1) {
+    return;
+  }
+
+  syscall(SYS_tkill, child_pid_, SIGKILL);
+}
+
+void PtracerThread::SetTracer(pid_t tracer_pid) {
+  prctl(PR_SET_PTRACER, tracer_pid);
+}
+
+void PtracerThread::ClearTracer() {
+  prctl(PR_SET_PTRACER, 0);
+}
+
+}  // namespace android