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.
 */

#ifndef __ANDROID_DLEXT_H__
#define __ANDROID_DLEXT_H__

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

/**
 * \file
 * Advanced dynamic library opening support. Most users will want to use
 * the standard [dlopen(3)](http://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,

  /**
   * When set, if the minimum `p_vaddr` of the ELF file's `PT_LOAD` segments is non-zero,
   * the dynamic linker will load it at that address.
   *
   * This flag is for ART internal use only.
   */
  ANDROID_DLEXT_FORCE_FIXED_VADDR = 0x80,

  /**
   * Instructs dlopen to load the library at the address specified by reserved_addr.
   *
   * The difference between `ANDROID_DLEXT_LOAD_AT_FIXED_ADDRESS` and
   * `ANDROID_DLEXT_RESERVED_ADDRESS` is that for `ANDROID_DLEXT_LOAD_AT_FIXED_ADDRESS` the linker
   * reserves memory at `reserved_addr` whereas for `ANDROID_DLEXT_RESERVED_ADDRESS` the linker
   * relies on the caller to reserve the memory.
   *
   * This flag can be used with `ANDROID_DLEXT_FORCE_FIXED_VADDR`. When
   * `ANDROID_DLEXT_FORCE_FIXED_VADDR` is set and `load_bias` is not 0 (`load_bias` is the
   * minimum `p_vaddr` of all `PT_LOAD` segments) this flag is ignored because the linker has to
   * pick one address over the other and this way is more convenient for ART.
   * Note that `ANDROID_DLEXT_FORCE_FIXED_VADDR` does not generate an error when the minimum
   * `p_vaddr` is 0.
   *
   * Cannot be used with `ANDROID_DLEXT_RESERVED_ADDRESS` or `ANDROID_DLEXT_RESERVED_ADDRESS_HINT`.
   *
   * This flag is for ART internal use only.
   */
  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,

  /** 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_FORCE_FIXED_VADDR |
                                        ANDROID_DLEXT_LOAD_AT_FIXED_ADDRESS |
                                        ANDROID_DLEXT_USE_NAMESPACE,
};

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*   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* library_namespace;
} android_dlextinfo;

/**
 * Opens the given library. The `__filename` and `__flags` arguments are
 * the same as for [dlopen(3)](http://man7.org/linux/man-pages/man3/dlopen.3.html),
 * with the Android-specific flags supplied via the `flags` member of `__info`.
 */
void* android_dlopen_ext(const char* __filename, int __flags, const android_dlextinfo* __info)
  __INTRODUCED_IN(21);

__END_DECLS

#endif