Home | History | Annotate | Download | only in linker 
      1 // Copyright 2015 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 // Definitions for android_dlopen_ext().
      6 //
      7 // This function was added for Android L-MR1 and made available in android-21
      8 // but we currently build Chromium with android-16. Placing the declarations
      9 // we need here allows code that uses android_dlopen_ext() to build with
     10 // android-16. At runtime we check the target's SDK_INT to ensure that we
     11 // are on a system new enough to offer this function, and also only access
     12 // it with dlsym so that the runtime linker on pre-Android L-MR1 targets will
     13 // not complain about a missing symbol when loading our library.
     14 //
     15 // Details below taken from:
     16 //   third_party/android_tools/ndk/platforms/android-21
     17 //       /arch-arm/usr/include/android/dlext.h
     18 //
     19 // Although taken specifically from arch-arm, there are no architecture-
     20 // specific elements in dlext.h. All android-21/arch-* directories contain
     21 // identical copies of dlext.h.
     22 
     23 #ifndef BASE_ANDROID_LINKER_ANDROID_DLEXT_H_
     24 #define BASE_ANDROID_LINKER_ANDROID_DLEXT_H_
     25 
     26 #include <stddef.h>
     27 #include <stdint.h>
     28 
     29 /* bitfield definitions for android_dlextinfo.flags */
     30 enum {
     31   /* When set, the reserved_addr and reserved_size fields must point to an
     32    * already-reserved region of address space which will be used to load the
     33    * library if it fits. If the reserved region is not large enough, the load
     34    * will fail.
     35    */
     36   ANDROID_DLEXT_RESERVED_ADDRESS      = 0x1,
     37 
     38   /* As DLEXT_RESERVED_ADDRESS, but if the reserved region is not large enough,
     39    * the linker will choose an available address instead.
     40    */
     41   ANDROID_DLEXT_RESERVED_ADDRESS_HINT = 0x2,
     42 
     43   /* When set, write the GNU RELRO section of the mapped library to relro_fd
     44    * after relocation has been performed, to allow it to be reused by another
     45    * process loading the same library at the same address. This implies
     46    * ANDROID_DLEXT_USE_RELRO.
     47    */
     48   ANDROID_DLEXT_WRITE_RELRO           = 0x4,
     49 
     50   /* When set, compare the GNU RELRO section of the mapped library to relro_fd
     51    * after relocation has been performed, and replace any relocated pages that
     52    * are identical with a version mapped from the file.
     53    */
     54   ANDROID_DLEXT_USE_RELRO             = 0x8,
     55 
     56   /* Instruct dlopen to use library_fd instead of opening file by name.
     57    * The filename parameter is still used to identify the library.
     58    */
     59   ANDROID_DLEXT_USE_LIBRARY_FD        = 0x10,
     60 
     61   /* Mask of valid bits */
     62   ANDROID_DLEXT_VALID_FLAG_BITS       = ANDROID_DLEXT_RESERVED_ADDRESS |
     63                                         ANDROID_DLEXT_RESERVED_ADDRESS_HINT |
     64                                         ANDROID_DLEXT_WRITE_RELRO |
     65                                         ANDROID_DLEXT_USE_RELRO |
     66                                         ANDROID_DLEXT_USE_LIBRARY_FD,
     67 };
     68 
     69 typedef struct {
     70   uint64_t flags;
     71   void*   reserved_addr;
     72   size_t  reserved_size;
     73   int     relro_fd;
     74   int     library_fd;
     75 } android_dlextinfo;
     76 
     77 #endif  // BASE_ANDROID_LINKER_ANDROID_DLEXT_H_
     78