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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 <signal.h>
#include <sys/mman.h>
#include "base/globals.h"
#include "base/bit_utils.h"
#include "thread.h"
namespace art HIDDEN {
void Thread::SetUpAlternateSignalStack() {
// Bionic does this for us.
}
void Thread::TearDownAlternateSignalStack() {
// Bionic does this for us.
}
void Thread::MadviseAwayAlternateSignalStack() {
stack_t old_ss;
int result = sigaltstack(nullptr, &old_ss);
CHECK_EQ(result, 0);
// Only call `madvise()` on enabled page-aligned alternate signal stack. Processes can
// create different arbitrary alternate signal stacks and we do not want to erroneously
// `madvise()` away pages that may hold data other than the alternate signal stack.
if ((old_ss.ss_flags & SS_DISABLE) == 0 &&
IsAlignedParam(old_ss.ss_sp, gPageSize) &&
IsAlignedParam(old_ss.ss_size, gPageSize)) {
CHECK_EQ(old_ss.ss_flags & SS_ONSTACK, 0);
// Note: We're testing and benchmarking ART on devices with old kernels
// which may not support `MADV_FREE`, so we do not check the result.
// It should succeed on devices with Android 12+.
madvise(old_ss.ss_sp, old_ss.ss_size, MADV_FREE);
}
}
} // namespace art
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