fixes golang#32912

The crash occurs when go runtime calls a VDSO function (say
__vdso_clock_gettime) and a signal arrives to that thread.
Since VDSO functions temporarily destroy the G register (R10),
Go functions asynchronously executed in that thread (i.e. Go's signal
handler) can try to load data from the destroyed G, which causes
segmentation fault.

src/runtime/crash_test.go

@@ -144,6 +144,7 @@ func buildTestProg(t *testing.T, binary string, flags ...string) (string, error)
 }
 
 func TestVDSO(t *testing.T) {
+	t.Parallel()
 	output := runTestProg(t, "testprog", "SignalInVDSO")
 	want := "success\n"
 	if output != want {

src/runtime/signal_unix.go

@@ -274,6 +274,21 @@ func sigpipe() {
 	dieFromSignal(_SIGPIPE)
 }
 
+// sigFetchG fetches the value of G safely when running in a signal handler.
+// On some architectures, the g value may be clobbered when running in a VDSO.
+// See issue #32912.
+//
+//go:nosplit
+func sigFetchG(c *sigctxt) *g {
+    switch GOARCH {
+    case "arm", "arm64", "ppc64", "ppc64le":
+        if inVDSOPage(c.sigpc()) {
+            return nil
+        }
+    }
+    return getg()
+}
+
 // sigtrampgo is called from the signal handler function, sigtramp,
 // written in assembly code.
 // This is called by the signal handler, and the world may be stopped.
@@ -289,9 +304,9 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 	if sigfwdgo(sig, info, ctx) {
 		return
 	}
-	g := getg()
+	c := &sigctxt{info, ctx}
+	g := sigFetchG(c)
 	if g == nil {
-		c := &sigctxt{info, ctx}
 		if sig == _SIGPROF {
 			sigprofNonGoPC(c.sigpc())
 			return
@@ -347,7 +362,6 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 		signalDuringFork(sig)
 	}
 
-	c := &sigctxt{info, ctx}
 	c.fixsigcode(sig)
 	sighandler(sig, info, ctx, g)
 	setg(g)
@@ -657,9 +671,10 @@ func sigfwdgo(sig uint32, info *siginfo, ctx unsafe.Pointer) bool {
 		return false
 	}
 	// Determine if the signal occurred inside Go code. We test that:
-	//   (1) we were in a goroutine (i.e., m.curg != nil), and
-	//   (2) we weren't in CGO.
-	g := getg()
+	//   (1) we weren't in VDSO page,
+	//   (2) we were in a goroutine (i.e., m.curg != nil), and
+	//   (3) we weren't in CGO.
+	g := sigFetchG(c)
 	if g != nil && g.m != nil && g.m.curg != nil && !g.m.incgo {
 		return false
 	}

src/runtime/testdata/testprog/vdso.go

@@ -33,8 +33,8 @@ func signalInVDSO() {
         t0 := time.Now()
         t1 := t0
         // We should get a profiling signal 100 times a second,
-        // so running for 10 seconds should be sufficient.
-        for t1.Sub(t0) < 10*time.Second {
+        // so running for 1 second should be sufficient.
+        for t1.Sub(t0) < time.Second {
                 t1 = time.Now()
         }
 

src/runtime/vdso_linux.go

@@ -281,6 +281,7 @@ func vdsoauxv(tag, val uintptr) {
 }
 
 // vdsoMarker reports whether PC is on the VDSO page.
+//go:nosplit
 func inVDSOPage(pc uintptr) bool {
 	for _, k := range vdsoSymbolKeys {
 		if *k.ptr != 0 {