1 /*
2  * Copyright (C) 2011 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 "thread.h"
18 
19 #include <signal.h>
20 
21 #include "base/logging.h"  // For VLOG.
22 #include "base/utils.h"
23 
24 namespace art {
25 
SigAltStack(stack_t * new_stack,stack_t * old_stack)26 static void SigAltStack(stack_t* new_stack, stack_t* old_stack) {
27   if (sigaltstack(new_stack, old_stack) == -1) {
28     PLOG(FATAL) << "sigaltstack failed";
29   }
30 }
31 
32 // The default SIGSTKSZ on linux is 8K.  If we do any logging in a signal
33 // handler or do a stack unwind, this is too small.  We allocate 32K
34 // instead of the minimum signal stack size.
35 // TODO: We shouldn't do logging (with locks) in signal handlers.
36 static constexpr int kHostAltSigStackSize =
37     32 * KB < MINSIGSTKSZ ? MINSIGSTKSZ : 32 * KB;
38 
SetUpAlternateSignalStack()39 void Thread::SetUpAlternateSignalStack() {
40   // Create and set an alternate signal stack.
41 #ifdef ART_TARGET_ANDROID
42   LOG(FATAL) << "Invalid use of alternate signal stack on Android";
43 #endif
44   stack_t ss;
45   ss.ss_sp = new uint8_t[kHostAltSigStackSize];
46   ss.ss_size = kHostAltSigStackSize;
47   ss.ss_flags = 0;
48   CHECK(ss.ss_sp != nullptr);
49   SigAltStack(&ss, nullptr);
50 
51   // Double-check that it worked.
52   ss.ss_sp = nullptr;
53   SigAltStack(nullptr, &ss);
54   VLOG(threads) << "Alternate signal stack is " << PrettySize(ss.ss_size) << " at " << ss.ss_sp;
55 }
56 
TearDownAlternateSignalStack()57 void Thread::TearDownAlternateSignalStack() {
58   // Get the pointer so we can free the memory.
59   stack_t ss;
60   SigAltStack(nullptr, &ss);
61   uint8_t* allocated_signal_stack = reinterpret_cast<uint8_t*>(ss.ss_sp);
62 
63   // Tell the kernel to stop using it.
64   ss.ss_sp = nullptr;
65   ss.ss_flags = SS_DISABLE;
66   ss.ss_size = kHostAltSigStackSize;  // Avoid ENOMEM failure with Mac OS' buggy libc.
67   SigAltStack(&ss, nullptr);
68 
69   // Free it.
70   delete[] allocated_signal_stack;
71 }
72 
73 }  // namespace art
74