libc/include/android/dlext.h

/*
 * Copyright (C) 2014 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.
 */

#pragma once

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <sys/cdefs.h>
#include <sys/types.h>  /* for off64_t */

/**
 * @addtogroup libdl Dynamic Linker
 * @{
 */

/**
 * \file
 * Advanced dynamic library opening support. Most users will want to use
 * the standard [dlopen(3)](https://man7.org/linux/man-pages/man3/dlopen.3.html)
 * functionality in `<dlfcn.h>` instead.
 */

__BEGIN_DECLS

/** Bitfield definitions for `android_dlextinfo::flags`. */
enum {
  /**
   * When set, the `reserved_addr` and `reserved_size` fields must point to an
   * already-reserved region of address space which will be used to load the
   * library if it fits.
   *
   * If the reserved region is not large enough, loading will fail.
   */
  ANDROID_DLEXT_RESERVED_ADDRESS      = 0x1,

  /**
   * Like `ANDROID_DLEXT_RESERVED_ADDRESS`, but if the reserved region is not large enough,
   * the linker will choose an available address instead.
   */
  ANDROID_DLEXT_RESERVED_ADDRESS_HINT = 0x2,

  /**
   * When set, write the GNU RELRO section of the mapped library to `relro_fd`
   * after relocation has been performed, to allow it to be reused by another
   * process loading the same library at the same address. This implies
   * `ANDROID_DLEXT_USE_RELRO`.
   *
   * This is mainly useful for the system WebView implementation.
   */
  ANDROID_DLEXT_WRITE_RELRO           = 0x4,

  /**
   * When set, compare the GNU RELRO section of the mapped library to `relro_fd`
   * after relocation has been performed, and replace any relocated pages that
   * are identical with a version mapped from the file.
   *
   * This is mainly useful for the system WebView implementation.
   */
  ANDROID_DLEXT_USE_RELRO             = 0x8,

  /**
   * Use `library_fd` instead of opening the file by name.
   * The filename parameter is still used to identify the library.
   */
  ANDROID_DLEXT_USE_LIBRARY_FD        = 0x10,

  /**
   * If opening a library using `library_fd` read it starting at `library_fd_offset`.
   * This is mainly useful for loading a library stored within another file (such as uncompressed
   * inside a ZIP archive).
   * This flag is only valid when `ANDROID_DLEXT_USE_LIBRARY_FD` is set.
   */
  ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET    = 0x20,

  /**
   * When set, do not use `stat(2)` to check if the library has already been loaded.
   *
   * This flag allows forced loading of the library in the case when for some
   * reason multiple ELF files share the same filename (because the already-loaded
   * library has been removed and overwritten, for example).
   *
   * Note that if the library has the same `DT_SONAME` as an old one and some other
   * library has the soname in its `DT_NEEDED` list, the first one will be used to resolve any
   * dependencies.
   */
  ANDROID_DLEXT_FORCE_LOAD = 0x40,

  // Historically we had two other options for ART.
  // They were last available in API level 28.
  // Reuse these bits last!
  // ANDROID_DLEXT_FORCE_FIXED_VADDR = 0x80
  // ANDROID_DLEXT_LOAD_AT_FIXED_ADDRESS = 0x100

  /**
   * This flag used to load library in a different namespace. The namespace is
   * specified in `library_namespace`.
   *
   * This flag is for internal use only (since there is no NDK API for namespaces).
   */
  ANDROID_DLEXT_USE_NAMESPACE = 0x200,

  /**
   * Instructs dlopen() to apply `ANDROID_DLEXT_RESERVED_ADDRESS`,
   * `ANDROID_DLEXT_RESERVED_ADDRESS_HINT`, `ANDROID_DLEXT_WRITE_RELRO` and
   * `ANDROID_DLEXT_USE_RELRO` to any libraries loaded as dependencies of the
   * main library as well.
   *
   * This means that if the main library depends on one or more not-already-loaded libraries, they
   * will be loaded consecutively into the region starting at `reserved_addr`, and `reserved_size`
   * must be large enough to contain all of the libraries. The libraries will be loaded in the
   * deterministic order constructed from the DT_NEEDED entries, rather than the more secure random
   * order used by default.
   *
   * Each library's GNU RELRO sections will be written out to `relro_fd` in the same order they were
   * loaded. This will mean that the resulting file is dependent on which of the libraries were
   * already loaded, as only the newly loaded libraries will be included, not any already-loaded
   * dependencies. The caller should ensure that the set of libraries newly loaded is consistent
   * for this to be effective.
   *
   * This is mainly useful for the system WebView implementation.
   */
  ANDROID_DLEXT_RESERVED_ADDRESS_RECURSIVE = 0x400,


  /** Mask of valid bits. */
  ANDROID_DLEXT_VALID_FLAG_BITS       = ANDROID_DLEXT_RESERVED_ADDRESS |
                                        ANDROID_DLEXT_RESERVED_ADDRESS_HINT |
                                        ANDROID_DLEXT_WRITE_RELRO |
                                        ANDROID_DLEXT_USE_RELRO |
                                        ANDROID_DLEXT_USE_LIBRARY_FD |
                                        ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET |
                                        ANDROID_DLEXT_FORCE_LOAD |
                                        ANDROID_DLEXT_USE_NAMESPACE |
                                        ANDROID_DLEXT_RESERVED_ADDRESS_RECURSIVE,
};

struct android_namespace_t;

/** Used to pass Android-specific arguments to android_dlopen_ext(). */
typedef struct {
  /** A bitmask of `ANDROID_DLEXT_` enum values. */
  uint64_t flags;

  /** Used by `ANDROID_DLEXT_RESERVED_ADDRESS` and `ANDROID_DLEXT_RESERVED_ADDRESS_HINT`. */
  void*   _Nullable reserved_addr;
  /** Used by `ANDROID_DLEXT_RESERVED_ADDRESS` and `ANDROID_DLEXT_RESERVED_ADDRESS_HINT`. */
  size_t  reserved_size;

  /** Used by `ANDROID_DLEXT_WRITE_RELRO` and `ANDROID_DLEXT_USE_RELRO`. */
  int     relro_fd;

  /** Used by `ANDROID_DLEXT_USE_LIBRARY_FD`. */
  int     library_fd;
  /** Used by `ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET` */
  off64_t library_fd_offset;

  /** Used by `ANDROID_DLEXT_USE_NAMESPACE`. */
  struct android_namespace_t* _Nullable library_namespace;
} android_dlextinfo;

/**
 * Opens the given library. The `__filename` and `__flags` arguments are
 * the same as for [dlopen(3)](https://man7.org/linux/man-pages/man3/dlopen.3.html),
 * with the Android-specific flags supplied via the `flags` member of `__info`.
 */
void* _Nullable android_dlopen_ext(const char* _Nullable __filename, int __flags, const android_dlextinfo* _Nullable __info);

__END_DECLS

/** @} */