// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build arm64
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package runtime
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import "internal/cpu"
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var randomNumber uint32
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func archauxv(tag, val uintptr) {
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switch tag {
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case _AT_RANDOM:
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// sysargs filled in startupRandomData, but that
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// pointer may not be word aligned, so we must treat
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// it as a byte array.
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randomNumber = uint32(startupRandomData[4]) | uint32(startupRandomData[5])<<8 |
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uint32(startupRandomData[6])<<16 | uint32(startupRandomData[7])<<24
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case _AT_HWCAP:
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// arm64 doesn't have a 'cpuid' instruction equivalent and relies on
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// HWCAP/HWCAP2 bits for hardware capabilities.
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hwcap := uint(val)
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if GOOS == "android" {
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// The Samsung S9+ kernel reports support for atomics, but not all cores
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// actually support them, resulting in SIGILL. See issue #28431.
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// TODO(elias.naur): Only disable the optimization on bad chipsets.
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const hwcap_ATOMICS = 1 << 8
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hwcap &= ^uint(hwcap_ATOMICS)
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}
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cpu.HWCap = hwcap
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case _AT_HWCAP2:
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cpu.HWCap2 = uint(val)
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}
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}
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//go:nosplit
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func cputicks() int64 {
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// Currently cputicks() is used in blocking profiler and to seed fastrand().
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// nanotime() is a poor approximation of CPU ticks that is enough for the profiler.
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// randomNumber provides better seeding of fastrand.
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return nanotime() + int64(randomNumber)
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}
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