1 /*
2 * Copyright (C) 2023 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "berberis/guest_loader/guest_loader.h"
18
19 #include <link.h>
20
21 #include "berberis/base/macros.h"
22 #include "berberis/base/tracing.h"
23 #include "berberis/instrument/loader.h"
24
25 #include "guest_loader_impl.h" // MakeElfSymbolTrampolineCallable
26
27 namespace berberis {
28
29 namespace {
30
DoCustomTrampoline_rtld_db_dlactivity(HostCode callee,ThreadState * state)31 void DoCustomTrampoline_rtld_db_dlactivity(HostCode callee, ThreadState* state) {
32 UNUSED(callee, state);
33
34 // It would be also tempting to bind r_debug to callee, but then we need to know r_debug when
35 // creating the trampoline. Also, it seems r_debug might still be 0 when rtld_db_dlactivity is
36 // called first couple of times.
37 // Thus, search and check.
38 const auto* debug = GuestLoader::GetInstance()->FindRDebug();
39 if (debug == nullptr) {
40 return;
41 }
42
43 // ATTENTION: assume struct r_debug and struct link_map are compatible!
44 if (debug->r_state == r_debug::RT_CONSISTENT) {
45 OnConsistentLinkMap(debug->r_map);
46 }
47 }
48
49 } // namespace
50
InitLinkerDebug(const LoadedElfFile & linker_elf_file)51 void InitLinkerDebug(const LoadedElfFile& linker_elf_file) {
52 if (!kInstrumentLoader) {
53 return;
54 }
55
56 // The correct way to hook linker rtld_db_dlactivity would be to read struct r_debug pointer from
57 // main executable's DT_DEBUG and get breakpoint address from there.
58 // Unfortunately, DT_DEBUG gets initialized by guest linker, which didn't yet run at this point.
59 // Instead, hope breakpoint symbol is exported.
60 std::string error_msg;
61 if (!MakeElfSymbolTrampolineCallable(linker_elf_file,
62 "linker",
63 "rtld_db_dlactivity",
64 DoCustomTrampoline_rtld_db_dlactivity,
65 nullptr,
66 &error_msg)) {
67 TRACE("failed to hook rtld_db_dlactivity: %s", error_msg.c_str());
68 }
69 }
70
71 } // namespace berberis