7 files changed, 47 insertions, 9 deletions
diff --git a/src/internal/trace/testdata/testprog/stacks.go b/src/internal/trace/testdata/testprog/stacks.go
index e64bc86844..478daa0d94 100644
--- a/src/internal/trace/testdata/testprog/stacks.go
+++ b/src/internal/trace/testdata/testprog/stacks.go
@@ -97,6 +97,11 @@ func main() {
 		rp.Read(data[:])
 		pipeReadDone <- true
 	}()
+	go func() { // func12
+		for {
+			syncPreemptPoint()
+		}
+	}()
 
 	time.Sleep(100 * time.Millisecond)
 	runtime.GC()
@@ -127,3 +132,12 @@ func main() {
 
 	runtime.GOMAXPROCS(oldGoMaxProcs)
 }
+
+//go:noinline
+func syncPreemptPoint() {
+	if never {
+		syncPreemptPoint()
+	}
+}
+
+var never bool
diff --git a/src/internal/trace/trace_test.go b/src/internal/trace/trace_test.go
index eaf194cf07..44b7055344 100644
--- a/src/internal/trace/trace_test.go
+++ b/src/internal/trace/trace_test.go
@@ -326,7 +326,8 @@ func TestTraceStacks(t *testing.T) {
 		const mainLine = 21
 		want := []evDesc{
 			{trace.EventStateTransition, "Goroutine Running->Runnable", []frame{
-				{"main.main", mainLine + 82},
+				{"runtime.Gosched", 0},
+				{"main.main", mainLine + 87},
 			}},
 			{trace.EventStateTransition, "Goroutine NotExist->Runnable", []frame{
 				{"main.main", mainLine + 11},
@@ -349,7 +350,7 @@ func TestTraceStacks(t *testing.T) {
 			}},
 			{trace.EventStateTransition, "Goroutine Waiting->Runnable", []frame{
 				{"runtime.chansend1", 0},
-				{"main.main", mainLine + 84},
+				{"main.main", mainLine + 89},
 			}},
 			{trace.EventStateTransition, "Goroutine Running->Waiting", []frame{
 				{"runtime.chansend1", 0},
@@ -357,7 +358,7 @@ func TestTraceStacks(t *testing.T) {
 			}},
 			{trace.EventStateTransition, "Goroutine Waiting->Runnable", []frame{
 				{"runtime.chanrecv1", 0},
-				{"main.main", mainLine + 85},
+				{"main.main", mainLine + 90},
 			}},
 			{trace.EventStateTransition, "Goroutine Running->Waiting", []frame{
 				{"runtime.selectgo", 0},
@@ -365,7 +366,7 @@ func TestTraceStacks(t *testing.T) {
 			}},
 			{trace.EventStateTransition, "Goroutine Waiting->Runnable", []frame{
 				{"runtime.selectgo", 0},
-				{"main.main", mainLine + 86},
+				{"main.main", mainLine + 91},
 			}},
 			{trace.EventStateTransition, "Goroutine Running->Waiting", []frame{
 				{"sync.(*Mutex).Lock", 0},
@@ -382,7 +383,7 @@ func TestTraceStacks(t *testing.T) {
 			{trace.EventStateTransition, "Goroutine Waiting->Runnable", []frame{
 				{"sync.(*WaitGroup).Add", 0},
 				{"sync.(*WaitGroup).Done", 0},
-				{"main.main", mainLine + 91},
+				{"main.main", mainLine + 96},
 			}},
 			{trace.EventStateTransition, "Goroutine Running->Waiting", []frame{
 				{"sync.(*Cond).Wait", 0},
@@ -402,6 +403,10 @@ func TestTraceStacks(t *testing.T) {
 				{"runtime.GOMAXPROCS", 0},
 				{"main.main", 0},
 			}},
+			{trace.EventStateTransition, "Goroutine Running->Runnable", []frame{
+				{"main.syncPreemptPoint", 0},
+				{"main.main.func12", 0},
+			}},
 		}
 		if !stress {
 			// Only check for this stack if !stress because traceAdvance alone could
diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 9817308430..0376f7812b 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -3307,10 +3307,10 @@ func execute(gp *g, inheritTime bool) {
 		tryRecordGoroutineProfile(gp, nil, osyield)
 	}
 
-	// Assign gp.m before entering _Grunning so running Gs have an
-	// M.
+	// Assign gp.m before entering _Grunning so running Gs have an M.
 	mp.curg = gp
 	gp.m = mp
+	gp.syncSafePoint = false // Clear the flag, which may have been set by morestack.
 	casgstatus(gp, _Grunnable, _Grunning)
 	gp.waitsince = 0
 	gp.preempt = false
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 96720846b2..49a2ba2752 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -466,6 +466,7 @@ type g struct {
 	runnableTime    int64 // the amount of time spent runnable, cleared when running, only used when tracking
 	lockedm         muintptr
 	fipsIndicator   uint8
+	syncSafePoint   bool // set if g is stopped at a synchronous safe point.
 	runningCleanups atomic.Bool
 	sig             uint32
 	writebuf        []byte
diff --git a/src/runtime/stack.go b/src/runtime/stack.go
index 4b647976f0..a338708d76 100644
--- a/src/runtime/stack.go
+++ b/src/runtime/stack.go
@@ -1115,6 +1115,9 @@ func newstack() {
 			shrinkstack(gp)
 		}
 
+		// Set a flag indicated that we've been synchronously preempted.
+		gp.syncSafePoint = true
+
 		if gp.preemptStop {
 			preemptPark(gp) // never returns
 		}
diff --git a/src/runtime/traceruntime.go b/src/runtime/traceruntime.go
index 39adeb4c07..a2775a3427 100644
--- a/src/runtime/traceruntime.go
+++ b/src/runtime/traceruntime.go
@@ -457,7 +457,7 @@ func (tl traceLocker) GoPreempt() {
 
 // GoStop emits a GoStop event with the provided reason.
 func (tl traceLocker) GoStop(reason traceGoStopReason) {
-	tl.eventWriter(tracev2.GoRunning, tracev2.ProcRunning).event(tracev2.EvGoStop, traceArg(trace.goStopReasons[tl.gen%2][reason]), tl.stack(1))
+	tl.eventWriter(tracev2.GoRunning, tracev2.ProcRunning).event(tracev2.EvGoStop, traceArg(trace.goStopReasons[tl.gen%2][reason]), tl.stack(0))
 }
 
 // GoPark emits a GoBlock event with the provided reason.
diff --git a/src/runtime/tracestack.go b/src/runtime/tracestack.go
index bca2d0a88d..2ee68c85f0 100644
--- a/src/runtime/tracestack.go
+++ b/src/runtime/tracestack.go
@@ -109,7 +109,22 @@ func traceStack(skip int, gp *g, gen uintptr) uint64 {
 				nstk += 1 + fpTracebackPCs(unsafe.Pointer(gp.syscallbp), pcBuf[2:])
 			} else {
 				pcBuf[1] = gp.sched.pc
-				nstk += 1 + fpTracebackPCs(unsafe.Pointer(gp.sched.bp), pcBuf[2:])
+				if gp.syncSafePoint {
+					// We're stopped in morestack, which is an odd state because gp.sched.bp
+					// refers to our parent frame, since we haven't had the chance to push our
+					// frame pointer to the stack yet. If we just start walking from gp.sched.bp,
+					// we'll skip a frame as a result. Luckily, we can find the PC we want right
+					// at gp.sched.sp on non-LR platforms, and we have it directly on LR platforms.
+					// See issue go.dev/issue/68090.
+					if usesLR {
+						pcBuf[2] = gp.sched.lr
+					} else {
+						pcBuf[2] = *(*uintptr)(unsafe.Pointer(gp.sched.sp))
+					}
+					nstk += 2 + fpTracebackPCs(unsafe.Pointer(gp.sched.bp), pcBuf[3:])
+				} else {
+					nstk += 1 + fpTracebackPCs(unsafe.Pointer(gp.sched.bp), pcBuf[2:])
+				}
 			}
 		}
 	}