[release-branch.go1.23] cmd/trace: also show end stack traces

Fix a regression that appeared in 1.23 when it comes to the stack traces
shown in the trace viewer. In 1.22 and earlier, the viewer was always
showing end stack traces. In 1.23 and later the viewer started to
exclusively show start stack traces.

Showing only the start stack traces made it impossible to see the last
stack trace produced by a goroutine. It also made it hard to understand
why a goroutine went off-cpu, as one had to hunt down the next running
slice of the same goroutine.

Emit end stack traces in addition to start stack traces to fix the
issue.

Fixes #70592

Change-Id: Ib22ea61388c1d94cdbc99fae2d207c4dce011a59
Reviewed-on: https://go-review.googlesource.com/c/go/+/631895
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>
Auto-Submit: Felix Geisendörfer <[email protected]>
Reviewed-by: Nick Ripley <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
(cherry picked from commit 6405e60)
Reviewed-on: https://go-review.googlesource.com/c/go/+/632075
Reviewed-by: Veronica Silina <[email protected]>
Auto-Submit: Veronica Silina <[email protected]>

Author: felixge

src/cmd/trace/gstate.go

@@ -257,6 +257,10 @@ func (gs *gState[R]) stop(ts trace.Time, stack trace.Stack, ctx *traceContext) {
 	if gs.lastStopStack != trace.NoStack {
 		stk = ctx.Stack(viewerFrames(gs.lastStopStack))
 	}
+	var endStk int
+	if stack != trace.NoStack {
+		endStk = ctx.Stack(viewerFrames(stack))
+	}
 	// Check invariants.
 	if gs.startRunningTime == 0 {
 		panic("silently broken trace or generator invariant (startRunningTime != 0) not held")
@@ -270,6 +274,7 @@ func (gs *gState[R]) stop(ts trace.Time, stack trace.Stack, ctx *traceContext) {
 		Dur:      ts.Sub(gs.startRunningTime),
 		Resource: uint64(gs.executing),
 		Stack:    stk,
+		EndStack: endStk,
 	})
 
 	// Flush completed ranges.