runtime: print more information on stack overflow

Print the current SP and (old) stack bounds when the stack grows
too large. This helps to identify the problem: whether a large
stack is used, or something else goes wrong.

For #35470.

Change-Id: I34a4064d5c7280978391d835e171b90d06f87222
Reviewed-on: https://go-review.googlesource.com/c/go/+/207351
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

src/runtime/crash_test.go

@@ -204,9 +204,23 @@ func TestGoexitDeadlock(t *testing.T) {
 
 func TestStackOverflow(t *testing.T) {
 	output := runTestProg(t, "testprog", "StackOverflow")
-	want := "runtime: goroutine stack exceeds 1474560-byte limit\nfatal error: stack overflow"
-	if !strings.HasPrefix(output, want) {
-		t.Fatalf("output does not start with %q:\n%s", want, output)
+	want := []string{
+		"runtime: goroutine stack exceeds 1474560-byte limit\n",
+		"fatal error: stack overflow",
+		// information about the current SP and stack bounds
+		"runtime: sp=",
+		"stack=[",
+	}
+	if !strings.HasPrefix(output, want[0]) {
+		t.Errorf("output does not start with %q", want[0])
+	}
+	for _, s := range want[1:] {
+		if !strings.Contains(output, s) {
+			t.Errorf("output does not contain %q", s)
+		}
+	}
+	if t.Failed() {
+		t.Logf("output:\n%s", output)
 	}
 }
 

src/runtime/stack.go

@@ -1030,6 +1030,7 @@ func newstack() {
 	newsize := oldsize * 2
 	if newsize > maxstacksize {
 		print("runtime: goroutine stack exceeds ", maxstacksize, "-byte limit\n")
+		print("runtime: sp=", hex(sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n")
 		throw("stack overflow")
 	}