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// Copyright 2023 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 (freebsd && (386 || amd64 || arm || arm64 || riscv64)) || (linux && (386 || amd64 || arm || arm64 || loong64 || mips64 || mips64le || ppc64 || ppc64le || riscv64 || s390x))
package runtime_test
import (
"bytes"
"internal/testenv"
"os"
"os/exec"
"path/filepath"
"syscall"
"testing"
"time"
)
// TestUsingVDSO tests that we are actually using the VDSO to fetch
// the time.
func TestUsingVDSO(t *testing.T) {
const calls = 100
if os.Getenv("GO_WANT_HELPER_PROCESS") == "1" {
// Fetch the time a lot.
var total int64
for i := 0; i < calls; i++ {
total += time.Now().UnixNano()
}
os.Exit(0)
}
t.Parallel()
// Look for strace in /bin or /usr/bin. Don't assume that some
// strace on PATH is the one that we want.
strace := "/bin/strace"
if _, err := os.Stat(strace); err != nil {
strace = "/usr/bin/strace"
if _, err := os.Stat(strace); err != nil {
t.Skipf("skipping test because strace not found: %v", err)
}
}
exe, err := os.Executable()
if err != nil {
t.Skipf("skipping because Executable failed: %v", err)
}
t.Logf("GO_WANT_HELPER_PROCESS=1 %s -f -e clock_gettime %s -test.run=^TestUsingVDSO$", strace, exe)
cmd := testenv.Command(t, strace, "-f", "-e", "clock_gettime", exe, "-test.run=^TestUsingVDSO$")
cmd = testenv.CleanCmdEnv(cmd)
cmd.Env = append(cmd.Env, "GO_WANT_HELPER_PROCESS=1")
out, err := cmd.CombinedOutput()
if len(out) > 0 {
t.Logf("%s", out)
}
if err != nil {
if err := err.(*exec.ExitError); err != nil && err.Sys().(syscall.WaitStatus).Signaled() {
if !bytes.Contains(out, []byte("+++ killed by")) {
// strace itself occasionally crashes.
// Here, it exited with a signal, but
// the strace log didn't report any
// signal from the child process.
t.Log(err)
testenv.SkipFlaky(t, 63734)
}
}
t.Fatal(err)
}
if got := bytes.Count(out, []byte("gettime")); got >= calls {
t.Logf("found %d gettime calls, want < %d", got, calls)
// Try to double-check that a C program uses the VDSO.
tempdir := t.TempDir()
cfn := filepath.Join(tempdir, "time.c")
cexe := filepath.Join(tempdir, "time")
if err := os.WriteFile(cfn, []byte(vdsoCProgram), 0o644); err != nil {
t.Fatal(err)
}
cc := os.Getenv("CC")
if cc == "" {
cc, err = exec.LookPath("gcc")
if err != nil {
cc, err = exec.LookPath("clang")
if err != nil {
t.Skip("can't verify VDSO status, no C compiler")
}
}
}
t.Logf("%s -o %s %s", cc, cexe, cfn)
cmd = testenv.Command(t, cc, "-o", cexe, cfn)
cmd = testenv.CleanCmdEnv(cmd)
out, err = cmd.CombinedOutput()
if len(out) > 0 {
t.Logf("%s", out)
}
if err != nil {
t.Skipf("can't verify VDSO status, C compiled failed: %v", err)
}
t.Logf("%s -f -e clock_gettime %s", strace, cexe)
cmd = testenv.Command(t, strace, "-f", "-e", "clock_gettime", cexe)
cmd = testenv.CleanCmdEnv(cmd)
out, err = cmd.CombinedOutput()
if len(out) > 0 {
t.Logf("%s", out)
}
if err != nil {
t.Skipf("can't verify VDSO status, C program failed: %v", err)
}
if cgot := bytes.Count(out, []byte("gettime")); cgot >= 100 {
t.Logf("found %d gettime calls, want < %d", cgot, 100)
t.Log("C program does not use VDSO either")
return
}
// The Go program used the system call but the C
// program did not. This is a VDSO failure for Go.
t.Errorf("did not use VDSO system call")
}
}
const vdsoCProgram = `
#include <stdio.h>
#include <time.h>
int main() {
int i;
time_t tot;
for (i = 0; i < 100; i++) {
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
tot += ts.tv_nsec;
}
printf("%d\n", (int)(tot));
return 0;
}
`
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