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      1 /*
      2  * Copyright (C) 2016 The Android Open Source Project
      3  * All rights reserved.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions
      7  * are met:
      8  *  * Redistributions of source code must retain the above copyright
      9  *    notice, this list of conditions and the following disclaimer.
     10  *  * Redistributions in binary form must reproduce the above copyright
     11  *    notice, this list of conditions and the following disclaimer in
     12  *    the documentation and/or other materials provided with the
     13  *    distribution.
     14  *
     15  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     16  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     17  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
     18  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
     19  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
     20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
     21  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
     22  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
     23  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
     24  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
     25  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     26  * SUCH DAMAGE.
     27  */
     28 
     29 #include "linker_gdb_support.h"
     30 
     31 #include <pthread.h>
     32 
     33 #include "private/ScopedPthreadMutexLocker.h"
     34 
     35 // This function is an empty stub where GDB locates a breakpoint to get notified
     36 // about linker activity.
     37 extern "C"
     38 void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity();
     39 
     40 r_debug _r_debug =
     41     {1, nullptr, reinterpret_cast<uintptr_t>(&rtld_db_dlactivity), r_debug::RT_CONSISTENT, 0};
     42 
     43 static pthread_mutex_t g__r_debug_mutex = PTHREAD_MUTEX_INITIALIZER;
     44 static link_map* r_debug_tail = nullptr;
     45 
     46 void insert_link_map_into_debug_map(link_map* map) {
     47   // Stick the new library at the end of the list.
     48   // gdb tends to care more about libc than it does
     49   // about leaf libraries, and ordering it this way
     50   // reduces the back-and-forth over the wire.
     51   if (r_debug_tail != nullptr) {
     52     r_debug_tail->l_next = map;
     53     map->l_prev = r_debug_tail;
     54     map->l_next = nullptr;
     55   } else {
     56     _r_debug.r_map = map;
     57     map->l_prev = nullptr;
     58     map->l_next = nullptr;
     59   }
     60   r_debug_tail = map;
     61 }
     62 
     63 void remove_link_map_from_debug_map(link_map* map) {
     64   if (r_debug_tail == map) {
     65     r_debug_tail = map->l_prev;
     66   }
     67 
     68   if (map->l_prev) {
     69     map->l_prev->l_next = map->l_next;
     70   }
     71   if (map->l_next) {
     72     map->l_next->l_prev = map->l_prev;
     73   }
     74 }
     75 
     76 void notify_gdb_of_load(link_map* map) {
     77   ScopedPthreadMutexLocker locker(&g__r_debug_mutex);
     78 
     79   _r_debug.r_state = r_debug::RT_ADD;
     80   rtld_db_dlactivity();
     81 
     82   insert_link_map_into_debug_map(map);
     83 
     84   _r_debug.r_state = r_debug::RT_CONSISTENT;
     85   rtld_db_dlactivity();
     86 }
     87 
     88 void notify_gdb_of_unload(link_map* map) {
     89   ScopedPthreadMutexLocker locker(&g__r_debug_mutex);
     90 
     91   _r_debug.r_state = r_debug::RT_DELETE;
     92   rtld_db_dlactivity();
     93 
     94   remove_link_map_from_debug_map(map);
     95 
     96   _r_debug.r_state = r_debug::RT_CONSISTENT;
     97   rtld_db_dlactivity();
     98 }
     99 
    100 void notify_gdb_of_libraries() {
    101   _r_debug.r_state = r_debug::RT_ADD;
    102   rtld_db_dlactivity();
    103   _r_debug.r_state = r_debug::RT_CONSISTENT;
    104   rtld_db_dlactivity();
    105 }
    106 
    107