cpu_arm.go

     1  // Copyright 2017 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package cpu
     6  
     7  const CacheLinePadSize = 32
     8  
     9  // arm doesn't have a 'cpuid' equivalent, so we rely on HWCAP/HWCAP2.
    10  // These are initialized by archauxv() and should not be changed after they are
    11  // initialized.
    12  var HWCap uint
    13  var HWCap2 uint
    14  var Platform string
    15  
    16  // HWCAP/HWCAP2 bits. These are exposed by Linux and FreeBSD.
    17  const (
    18  	hwcap_VFPv4 = 1 << 16
    19  	hwcap_IDIVA = 1 << 17
    20  	hwcap_LPAE  = 1 << 20
    21  )
    22  
    23  func doinit() {
    24  	options = []option{
    25  		{Name: "vfpv4", Feature: &ARM.HasVFPv4},
    26  		{Name: "idiva", Feature: &ARM.HasIDIVA},
    27  		{Name: "v7atomics", Feature: &ARM.HasV7Atomics},
    28  	}
    29  
    30  	// HWCAP feature bits
    31  	ARM.HasVFPv4 = isSet(HWCap, hwcap_VFPv4)
    32  	ARM.HasIDIVA = isSet(HWCap, hwcap_IDIVA)
    33  	// lpae is required to make the 64-bit instructions LDRD and STRD (and variants) atomic.
    34  	// See ARMv7 manual section B1.6.
    35  	// We also need at least a v7 chip, for the DMB instruction.
    36  	ARM.HasV7Atomics = isSet(HWCap, hwcap_LPAE) && isV7(Platform)
    37  }
    38  
    39  func isSet(hwc uint, value uint) bool {
    40  	return hwc&value != 0
    41  }
    42  
    43  func isV7(s string) bool {
    44  	if s == "aarch64" {
    45  		return true
    46  	}
    47  	return s >= "v7" // will be something like v5, v7, v8, v8l
    48  }
    49
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