internal/trace: add end-of-generation signal to trace

This change takes the EvEndOfGeneration event and promotes it to a real
event that appears in the trace.

This allows the trace parser to unambiguously identify truncated traces
vs. broken traces. It also makes a lot of the logic around parsing
simpler, because there's no more batch spilling necessary.

Fixes #73904.

Change-Id: I37c359b32b6b5f894825aafc02921adeaacf2595
Reviewed-on: https://go-review.googlesource.com/c/go/+/693398
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 2 insertions, 19 deletions

diff --git a/src/runtime/trace.go b/src/runtime/trace.go
index 0d71ad445c..2c712469ea 100644
--- a/src/runtime/trace.go
+++ b/src/runtime/trace.go
@@ -754,24 +754,7 @@ func traceRegisterLabelsAndReasons(gen uintptr) {
 // was on has been returned, ReadTrace returns nil. The caller must copy the
 // returned data before calling ReadTrace again.
 // ReadTrace must be called from one goroutine at a time.
-func ReadTrace() []byte {
-	for {
-		buf := readTrace()
-
-		// Skip over the end-of-generation signal which must not appear
-		// in the final trace.
-		if len(buf) == 1 && tracev2.EventType(buf[0]) == tracev2.EvEndOfGeneration {
-			continue
-		}
-		return buf
-	}
-}
-
-// readTrace is the implementation of ReadTrace, except with an additional
-// in-band signal as to when the buffer is for a new generation.
-//
-//go:linkname readTrace runtime/trace.runtime_readTrace
-func readTrace() (buf []byte) {
+func ReadTrace() (buf []byte) {
 top:
 	var park bool
 	systemstack(func() {
@@ -842,7 +825,7 @@ func readTrace0() (buf []byte, park bool) {
 	if !trace.headerWritten {
 		trace.headerWritten = true
 		unlock(&trace.lock)
-		return []byte("go 1.25 trace\x00\x00\x00"), false
+		return []byte("go 1.26 trace\x00\x00\x00"), false
 	}
 
 	// Read the next buffer.