runtime: use saved state in SIGPROF handler for vDSO calls

VDSO calls do manual stack alignment, which doesn't get tracked in the
pcsp table. Without accurate pcsp information, backtracing them is
dangerous, and causes a crash in the SIGPROF handler. Fortunately,
https://golang.org/cl/97315 saves a clean state in m.vdsoPC/SP. Change
to use those if they're present, without attempting a normal backtrace.

Fixes #24925

Change-Id: I4b8501ae73a9d18209e22f839773c4fe6102a509
Reviewed-on: https://go-review.googlesource.com/107778
Run-TryBot: Heschi Kreinick <heschi@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/proc.go

@@ -3716,7 +3716,7 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) {
 	// transition. We simply require that g and SP match and that the PC is not
 	// in gogo.
 	traceback := true
-	if gp == nil || sp < gp.stack.lo || gp.stack.hi < sp || setsSP(pc) {
+	if gp == nil || sp < gp.stack.lo || gp.stack.hi < sp || setsSP(pc) || (mp != nil && mp.vdsoSP != 0) {
 		traceback = false
 	}
 	var stk [maxCPUProfStack]uintptr