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/*
* Copyright (C) 2011 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.
*/
#include "thread.h"
#include <signal.h>
#include "base/logging.h" // For VLOG.
#include "base/utils.h"
namespace art HIDDEN {
static void SigAltStack(stack_t* new_stack, stack_t* old_stack) {
if (sigaltstack(new_stack, old_stack) == -1) {
PLOG(FATAL) << "sigaltstack failed";
}
}
// The default SIGSTKSZ on linux is 8K. If we do any logging in a signal
// handler or do a stack unwind, this is too small. We allocate 32K
// instead of the minimum signal stack size.
// TODO: We shouldn't do logging (with locks) in signal handlers.
static constexpr int kHostAltSigStackSize =
32 * KB < MINSIGSTKSZ ? MINSIGSTKSZ : 32 * KB;
void Thread::SetUpAlternateSignalStack() {
// Create and set an alternate signal stack.
#ifdef ART_TARGET_ANDROID
LOG(FATAL) << "Invalid use of alternate signal stack on Android";
#endif
stack_t ss;
ss.ss_sp = new uint8_t[kHostAltSigStackSize];
ss.ss_size = kHostAltSigStackSize;
ss.ss_flags = 0;
CHECK(ss.ss_sp != nullptr);
SigAltStack(&ss, nullptr);
// Double-check that it worked.
ss.ss_sp = nullptr;
SigAltStack(nullptr, &ss);
VLOG(threads) << "Alternate signal stack is " << PrettySize(ss.ss_size) << " at " << ss.ss_sp;
}
void Thread::TearDownAlternateSignalStack() {
// Get the pointer so we can free the memory.
stack_t ss;
SigAltStack(nullptr, &ss);
uint8_t* allocated_signal_stack = reinterpret_cast<uint8_t*>(ss.ss_sp);
// Tell the kernel to stop using it.
ss.ss_sp = nullptr;
ss.ss_flags = SS_DISABLE;
ss.ss_size = kHostAltSigStackSize; // Avoid ENOMEM failure with Mac OS' buggy libc.
SigAltStack(&ss, nullptr);
// Free it.
delete[] allocated_signal_stack;
}
void Thread::MadviseAwayAlternateSignalStack() {
// We do not `madvise()` away the alternate signal stack on host.
}
} // namespace art