runtime: handle async fatal signals in VDSO

If we receive an async signal while running in the VDSO, such as a
SIGABRT or SIGSEGV sent from another process, we fail to print the
stacktrace with "runtime: unknown pc <vdso PC>".

We already have machinery to handle SIGPROF in the VDSO, but it isn't
hooked up for other signals. Add it to the general signal traceback
path.

This case is covered by TestSegv by making the test more strict w.r.t.
accepted output.

Fixes #47537

Change-Id: I755585f70e0c23e207e135bc6bd2aa68298e5d24
Reviewed-on: https://go-review.googlesource.com/c/go/+/339990
Trust: Michael Pratt <[email protected]>
Run-TryBot: Michael Pratt <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: prattmic

src/runtime/crash_cgo_test.go

@@ -526,13 +526,15 @@ func TestCgoTracebackSigpanic(t *testing.T) {
 	}
 	t.Parallel()
 	got := runTestProg(t, "testprogcgo", "TracebackSigpanic")
+	t.Log(got)
 	want := "runtime.sigpanic"
 	if !strings.Contains(got, want) {
-		t.Fatalf("want failure containing %q. output:\n%s\n", want, got)
+		t.Errorf("did not see %q in output", want)
 	}
-	nowant := "unexpected return pc"
+	// No runtime errors like "runtime: unexpected return pc".
+	nowant := "runtime: "
 	if strings.Contains(got, nowant) {
-		t.Fatalf("failure incorrectly contains %q. output:\n%s\n", nowant, got)
+		t.Errorf("unexpectedly saw %q in output", want)
 	}
 }
 
@@ -619,8 +621,14 @@ func TestSegv(t *testing.T) {
 			t.Parallel()
 			got := runTestProg(t, "testprogcgo", test)
 			t.Log(got)
-			if !strings.Contains(got, "SIGSEGV") {
-				t.Errorf("expected crash from signal")
+			want := "SIGSEGV"
+			if !strings.Contains(got, want) {
+				t.Errorf("did not see %q in output", want)
+			}
+			// No runtime errors like "runtime: unknown pc".
+			nowant := "runtime: "
+			if strings.Contains(got, nowant) {
+				t.Errorf("unexpectedly saw %q in output", want)
 			}
 		})
 	}

src/runtime/traceback.go

@@ -777,16 +777,23 @@ func traceback1(pc, sp, lr uintptr, gp *g, flags uint) {
 		printCgoTraceback(&cgoCallers)
 	}
 
-	var n int
 	if readgstatus(gp)&^_Gscan == _Gsyscall {
 		// Override registers if blocked in system call.
 		pc = gp.syscallpc
 		sp = gp.syscallsp
 		flags &^= _TraceTrap
 	}
+	if gp.m != nil && gp.m.vdsoSP != 0 {
+		// Override registers if running in VDSO. This comes after the
+		// _Gsyscall check to cover VDSO calls after entersyscall.
+		pc = gp.m.vdsoPC
+		sp = gp.m.vdsoSP
+		flags &^= _TraceTrap
+	}
+
 	// Print traceback. By default, omits runtime frames.
 	// If that means we print nothing at all, repeat forcing all frames printed.
-	n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags)
+	n := gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags)
 	if n == 0 && (flags&_TraceRuntimeFrames) == 0 {
 		n = gentraceback(pc, sp, lr, gp, 0, nil, _TracebackMaxFrames, nil, nil, flags|_TraceRuntimeFrames)
 	}