runtime: normalize sigprof traceback flags

Each gentraceback call uses a different set of flags. Combine these into
a common variable, only adjusted as necessary.

The effective changes here are:

* cgo traceback now has _TraceJumpStack. This is a no-op since it
  already passes curg.
* libcall traceback now has _TraceJumpStack. This is a behavior change
  and will allow following stack transitions if a libcall is performed on
  g0.
* VDSO traceback drops _TraceTrap. vdsoPC is a return address, so
  _TraceTrap was not necessary.

Change-Id: I351b3cb8dc77df7466795d5fbf2bd8f30bba2d37
Reviewed-on: https://go-review.googlesource.com/c/go/+/358900
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/proc.go

@@ -4645,6 +4645,7 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) {
 	getg().m.mallocing++
 
 	var stk [maxCPUProfStack]uintptr
+	flags := uint(_TraceJumpStack)
 	n := 0
 	if mp.ncgo > 0 && mp.curg != nil && mp.curg.syscallpc != 0 && mp.curg.syscallsp != 0 {
 		cgoOff := 0
@@ -4662,12 +4663,12 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) {
 		}
 
 		// Collect Go stack that leads to the cgo call.
-		n = gentraceback(mp.curg.syscallpc, mp.curg.syscallsp, 0, mp.curg, 0, &stk[cgoOff], len(stk)-cgoOff, nil, nil, 0)
+		n = gentraceback(mp.curg.syscallpc, mp.curg.syscallsp, 0, mp.curg, 0, &stk[cgoOff], len(stk)-cgoOff, nil, nil, flags)
 		if n > 0 {
 			n += cgoOff
 		}
 	} else {
-		n = gentraceback(pc, sp, lr, gp, 0, &stk[0], len(stk), nil, nil, _TraceTrap|_TraceJumpStack)
+		n = gentraceback(pc, sp, lr, gp, 0, &stk[0], len(stk), nil, nil, _TraceTrap|flags)
 	}
 
 	if n <= 0 {
@@ -4677,10 +4678,10 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) {
 		if usesLibcall() && mp.libcallg != 0 && mp.libcallpc != 0 && mp.libcallsp != 0 {
 			// Libcall, i.e. runtime syscall on windows.
 			// Collect Go stack that leads to the call.
-			n = gentraceback(mp.libcallpc, mp.libcallsp, 0, mp.libcallg.ptr(), 0, &stk[0], len(stk), nil, nil, 0)
+			n = gentraceback(mp.libcallpc, mp.libcallsp, 0, mp.libcallg.ptr(), 0, &stk[0], len(stk), nil, nil, flags)
 		}
 		if n == 0 && mp != nil && mp.vdsoSP != 0 {
-			n = gentraceback(mp.vdsoPC, mp.vdsoSP, 0, gp, 0, &stk[0], len(stk), nil, nil, _TraceTrap|_TraceJumpStack)
+			n = gentraceback(mp.vdsoPC, mp.vdsoSP, 0, gp, 0, &stk[0], len(stk), nil, nil, flags)
 		}
 		if n == 0 {
 			// If all of the above has failed, account it against abstract "System" or "GC".