cpu: parse /proc/cpuinfo on linux/arm64 on old kernels when needed
Updates tailscale/tailscale#5793
Fixes golang/go#57336
Change-Id: I4f8128bebcc58f265d447ecaaad2473aafa9131c
Reviewed-on: https://go-review.googlesource.com/c/sys/+/458315
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Auto-Submit: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
diff --git a/cpu/cpu_linux_arm64.go b/cpu/cpu_linux_arm64.go
index 79a38a0..a968b80 100644
--- a/cpu/cpu_linux_arm64.go
+++ b/cpu/cpu_linux_arm64.go
@@ -4,6 +4,11 @@
package cpu
+import (
+ "strings"
+ "syscall"
+)
+
// HWCAP/HWCAP2 bits. These are exposed by Linux.
const (
hwcap_FP = 1 << 0
@@ -32,10 +37,45 @@
hwcap_ASIMDFHM = 1 << 23
)
+// linuxKernelCanEmulateCPUID reports whether we're running
+// on Linux 4.11+. Ideally we'd like to ask the question about
+// whether the current kernel contains
+// https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=77c97b4ee21290f5f083173d957843b615abbff2
+// but the version number will have to do.
+func linuxKernelCanEmulateCPUID() bool {
+ var un syscall.Utsname
+ syscall.Uname(&un)
+ var sb strings.Builder
+ for _, b := range un.Release[:] {
+ if b == 0 {
+ break
+ }
+ sb.WriteByte(byte(b))
+ }
+ major, minor, _, ok := parseRelease(sb.String())
+ return ok && (major > 4 || major == 4 && minor >= 11)
+}
+
func doinit() {
if err := readHWCAP(); err != nil {
- // failed to read /proc/self/auxv, try reading registers directly
- readARM64Registers()
+ // We failed to read /proc/self/auxv. This can happen if the binary has
+ // been given extra capabilities(7) with /bin/setcap.
+ //
+ // When this happens, we have two options. If the Linux kernel is new
+ // enough (4.11+), we can read the arm64 registers directly which'll
+ // trap into the kernel and then return back to userspace.
+ //
+ // But on older kernels, such as Linux 4.4.180 as used on many Synology
+ // devices, calling readARM64Registers (specifically getisar0) will
+ // cause a SIGILL and we'll die. So for older kernels, parse /proc/cpuinfo
+ // instead.
+ //
+ // See golang/go#57336.
+ if linuxKernelCanEmulateCPUID() {
+ readARM64Registers()
+ } else {
+ readLinuxProcCPUInfo()
+ }
return
}
diff --git a/cpu/parse.go b/cpu/parse.go
new file mode 100644
index 0000000..762b63d
--- /dev/null
+++ b/cpu/parse.go
@@ -0,0 +1,43 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cpu
+
+import "strconv"
+
+// parseRelease parses a dot-separated version number. It follows the semver
+// syntax, but allows the minor and patch versions to be elided.
+//
+// This is a copy of the Go runtime's parseRelease from
+// https://golang.org/cl/209597.
+func parseRelease(rel string) (major, minor, patch int, ok bool) {
+ // Strip anything after a dash or plus.
+ for i := 0; i < len(rel); i++ {
+ if rel[i] == '-' || rel[i] == '+' {
+ rel = rel[:i]
+ break
+ }
+ }
+
+ next := func() (int, bool) {
+ for i := 0; i < len(rel); i++ {
+ if rel[i] == '.' {
+ ver, err := strconv.Atoi(rel[:i])
+ rel = rel[i+1:]
+ return ver, err == nil
+ }
+ }
+ ver, err := strconv.Atoi(rel)
+ rel = ""
+ return ver, err == nil
+ }
+ if major, ok = next(); !ok || rel == "" {
+ return
+ }
+ if minor, ok = next(); !ok || rel == "" {
+ return
+ }
+ patch, ok = next()
+ return
+}
diff --git a/cpu/parse_test.go b/cpu/parse_test.go
new file mode 100644
index 0000000..5a35881
--- /dev/null
+++ b/cpu/parse_test.go
@@ -0,0 +1,38 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cpu
+
+import "testing"
+
+type parseReleaseTest struct {
+ in string
+ major, minor, patch int
+}
+
+var parseReleaseTests = []parseReleaseTest{
+ {"", -1, -1, -1},
+ {"x", -1, -1, -1},
+ {"5", 5, 0, 0},
+ {"5.12", 5, 12, 0},
+ {"5.12-x", 5, 12, 0},
+ {"5.12.1", 5, 12, 1},
+ {"5.12.1-x", 5, 12, 1},
+ {"5.12.1.0", 5, 12, 1},
+ {"5.20496382327982653440", -1, -1, -1},
+}
+
+func TestParseRelease(t *testing.T) {
+ for _, test := range parseReleaseTests {
+ major, minor, patch, ok := parseRelease(test.in)
+ if !ok {
+ major, minor, patch = -1, -1, -1
+ }
+ if test.major != major || test.minor != minor || test.patch != patch {
+ t.Errorf("parseRelease(%q) = (%v, %v, %v) want (%v, %v, %v)",
+ test.in, major, minor, patch,
+ test.major, test.minor, test.patch)
+ }
+ }
+}
diff --git a/cpu/proc_cpuinfo_linux.go b/cpu/proc_cpuinfo_linux.go
new file mode 100644
index 0000000..d87bd6b
--- /dev/null
+++ b/cpu/proc_cpuinfo_linux.go
@@ -0,0 +1,54 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build linux && arm64
+// +build linux,arm64
+
+package cpu
+
+import (
+ "errors"
+ "io"
+ "os"
+ "strings"
+)
+
+func readLinuxProcCPUInfo() error {
+ f, err := os.Open("/proc/cpuinfo")
+ if err != nil {
+ return err
+ }
+ defer f.Close()
+
+ var buf [1 << 10]byte // enough for first CPU
+ n, err := io.ReadFull(f, buf[:])
+ if err != nil && err != io.ErrUnexpectedEOF {
+ return err
+ }
+ in := string(buf[:n])
+ const features = "\nFeatures : "
+ i := strings.Index(in, features)
+ if i == -1 {
+ return errors.New("no CPU features found")
+ }
+ in = in[i+len(features):]
+ if i := strings.Index(in, "\n"); i != -1 {
+ in = in[:i]
+ }
+ m := map[string]*bool{}
+
+ initOptions() // need it early here; it's harmless to call twice
+ for _, o := range options {
+ m[o.Name] = o.Feature
+ }
+ // The EVTSTRM field has alias "evstrm" in Go, but Linux calls it "evtstrm".
+ m["evtstrm"] = &ARM64.HasEVTSTRM
+
+ for _, f := range strings.Fields(in) {
+ if p, ok := m[f]; ok {
+ *p = true
+ }
+ }
+ return nil
+}
