From 810ea0957517bcfc459627aeb10a3594340c895b Mon Sep 17 00:00:00 2001
From: Jamie Liu <jamieliu@google.com>
Date: Wed, 1 Sep 2021 10:27:30 -0700
Subject: Cache cpuid.HostFeatureSet().

PiperOrigin-RevId: 394261815
---
 pkg/cpuid/cpuid.go       |  8 ++++++++
 pkg/cpuid/cpuid_arm64.go | 14 ++++++++++++--
 pkg/cpuid/cpuid_x86.go   | 15 +++++++++++++--
 3 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/pkg/cpuid/cpuid.go b/pkg/cpuid/cpuid.go
index 69eeb7528..4d5e062a8 100644
--- a/pkg/cpuid/cpuid.go
+++ b/pkg/cpuid/cpuid.go
@@ -37,6 +37,14 @@ package cpuid
 // arch/arm64/include/uapi/asm/hwcap.h
 type Feature int
 
+// HostFeatureSet returns a FeatureSet that matches that of the host machine.
+// Callers must not mutate the returned FeatureSet.
+func HostFeatureSet() *FeatureSet {
+	return hostFeatureSet
+}
+
+var hostFeatureSet = getHostFeatureSet()
+
 // ErrIncompatible is returned by FeatureSet.HostCompatible if fs is not a
 // subset of the host feature set.
 type ErrIncompatible struct {
diff --git a/pkg/cpuid/cpuid_arm64.go b/pkg/cpuid/cpuid_arm64.go
index 6e61d562f..04645aed5 100644
--- a/pkg/cpuid/cpuid_arm64.go
+++ b/pkg/cpuid/cpuid_arm64.go
@@ -230,6 +230,16 @@ type FeatureSet struct {
 	CPURevision uint8
 }
 
+// Clone returns a copy of fs.
+func (fs *FeatureSet) Clone() *FeatureSet {
+	fs2 := *fs
+	fs2.Set = make(map[Feature]bool)
+	for f, b := range fs.Set {
+		fs2.Set[f] = b
+	}
+	return &fs2
+}
+
 // CheckHostCompatible returns nil if fs is a subset of the host feature set.
 // Noop on arm64.
 func (fs *FeatureSet) CheckHostCompatible() error {
@@ -292,9 +302,9 @@ func (fs FeatureSet) WriteCPUInfoTo(cpu uint, b *bytes.Buffer) {
 	fmt.Fprintln(b, "") // The /proc/cpuinfo file ends with an extra newline.
 }
 
-// HostFeatureSet uses hwCap to get host values and construct a feature set
+// getHostFeatureSet uses hwCap to get host values and construct a feature set
 // that matches that of the host machine.
-func HostFeatureSet() *FeatureSet {
+func getHostFeatureSet() *FeatureSet {
 	s := make(map[Feature]bool)
 
 	for f := range arm64FeatureStrings {
diff --git a/pkg/cpuid/cpuid_x86.go b/pkg/cpuid/cpuid_x86.go
index dc17cade8..a92d32d74 100644
--- a/pkg/cpuid/cpuid_x86.go
+++ b/pkg/cpuid/cpuid_x86.go
@@ -627,6 +627,17 @@ type FeatureSet struct {
 	CacheLine uint32
 }
 
+// Clone returns a copy of fs.
+func (fs *FeatureSet) Clone() *FeatureSet {
+	fs2 := *fs
+	fs2.Set = make(map[Feature]bool)
+	for f, b := range fs.Set {
+		fs2.Set[f] = b
+	}
+	fs2.Caches = append([]Cache(nil), fs.Caches...)
+	return &fs2
+}
+
 // FlagsString prints out supported CPU flags. If cpuinfoOnly is true, it is
 // equivalent to the "flags" field in /proc/cpuinfo.
 func (fs *FeatureSet) FlagsString(cpuinfoOnly bool) string {
@@ -961,13 +972,13 @@ func (fs *FeatureSet) UseXsaveopt() bool {
 // HostID executes a native CPUID instruction.
 func HostID(axArg, cxArg uint32) (ax, bx, cx, dx uint32)
 
-// HostFeatureSet uses cpuid to get host values and construct a feature set
+// getHostFeatureSet uses cpuid to get host values and construct a feature set
 // that matches that of the host machine. Note that there are several places
 // where there appear to be some unnecessary assignments between register names
 // (ax, bx, cx, or dx) and featureBlockN variables. This is to explicitly show
 // where the different feature blocks come from, to make the code easier to
 // inspect and read.
-func HostFeatureSet() *FeatureSet {
+func getHostFeatureSet() *FeatureSet {
 	// eax=0 gets max supported feature and vendor ID.
 	_, bx, cx, dx := HostID(0, 0)
 	vendorID := vendorIDFromRegs(bx, cx, dx)
-- 
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