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//go:build gc
package platform
import "runtime"
// CpuFeatures exposes the capabilities for this CPU, queried via the Has, HasExtra methods.
var CpuFeatures = loadCpuFeatureFlags()
// cpuFeatureFlags implements CpuFeatureFlags interface.
type cpuFeatureFlags struct {
isar0 uint64
isar1 uint64
}
// implemented in cpuid_arm64.s
func getisar0() uint64
// implemented in cpuid_arm64.s
func getisar1() uint64
func loadCpuFeatureFlags() CpuFeatureFlags {
switch runtime.GOOS {
case "darwin", "windows":
// These OSes do not allow userland to read the instruction set attribute registers,
// but basically require atomic instructions:
// - "darwin" is the desktop version (mobile version is "ios"),
// and the M1 is a ARMv8.4.
// - "windows" requires them from Windows 11, see page 12
// https://download.microsoft.com/download/7/8/8/788bf5ab-0751-4928-a22c-dffdc23c27f2/Minimum%20Hardware%20Requirements%20for%20Windows%2011.pdf
return &cpuFeatureFlags{
isar0: uint64(CpuFeatureArm64Atomic),
isar1: 0,
}
case "linux", "freebsd":
// These OSes allow userland to read the instruction set attribute registers,
// which is otherwise restricted to EL0:
// https://kernel.org/doc/Documentation/arm64/cpu-feature-registers.txt
// See these for contents of the registers:
// https://developer.arm.com/documentation/ddi0601/latest/AArch64-Registers/ID-AA64ISAR0-EL1--AArch64-Instruction-Set-Attribute-Register-0
// https://developer.arm.com/documentation/ddi0601/latest/AArch64-Registers/ID-AA64ISAR1-EL1--AArch64-Instruction-Set-Attribute-Register-1
return &cpuFeatureFlags{
isar0: getisar0(),
isar1: getisar1(),
}
default:
return &cpuFeatureFlags{}
}
}
// Has implements the same method on the CpuFeatureFlags interface.
func (f *cpuFeatureFlags) Has(cpuFeature CpuFeature) bool {
return (f.isar0 & uint64(cpuFeature)) != 0
}
// HasExtra implements the same method on the CpuFeatureFlags interface.
func (f *cpuFeatureFlags) HasExtra(cpuFeature CpuFeature) bool {
return (f.isar1 & uint64(cpuFeature)) != 0
}
// Raw implements the same method on the CpuFeatureFlags interface.
func (f *cpuFeatureFlags) Raw() uint64 {
// Below, we only set bits for the features we care about,
// instead of setting all the unnecessary bits obtained from the
// instruction set attribute registers.
var ret uint64
if f.Has(CpuFeatureArm64Atomic) {
ret = 1 << 0
}
return ret
}
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