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Panic when opening particular Go 1.25 trace #184
Description
I encountered this panic, running gotraceui from source at 40a0e49, using Go 1.25.2 for both running gotraceui and for producing my application's trace:
$ go run ./cmd/gotraceui/ /tmp/x.trace
# honnef.co/go/gotraceui/cmd/gotraceui
ld: warning: ignoring duplicate libraries: '-lobjc'
panic: runtime error: index out of range [-1]
goroutine 12 [running]:
honnef.co/go/gotraceui/trace/ptrace.processEvents(0x140000d2100, 0x1400061c000, 0x14000038908?)
.../go/src/honnef.co/go/gotraceui/trace/ptrace/ptrace.go:661 +0x4d08
honnef.co/go/gotraceui/trace/ptrace.Parse(0x140000d2100, 0x140000100c0)
.../go/src/honnef.co/go/gotraceui/trace/ptrace/ptrace.go:415 +0x1e0
main.loadTrace({_, _}, {_, _}, _)
.../go/src/honnef.co/go/gotraceui/cmd/gotraceui/main.go:1490 +0x14c
main.(*MainWindow).OpenTrace(0x140000f9b08, {0x101122338, 0x14000148080})
.../go/src/honnef.co/go/gotraceui/cmd/gotraceui/main.go:378 +0xd0
main.openTraceFromCmdline.func1()
.../go/src/honnef.co/go/gotraceui/cmd/gotraceui/main.go:1299 +0x50
created by main.openTraceFromCmdline in goroutine 1
.../go/src/honnef.co/go/gotraceui/cmd/gotraceui/main.go:1297 +0x19c
exit status 2
I was able to reproduce the troublesome trace it a couple times in a row with the particular benchmark I was developing, but then I tried changing a couple things, and then I was no longer able to generate an invalid trace.
I'm attaching a copy of the failed trace. I've redacted most of the strings related to the application, by overwriting application-specific strings with the same number of x characters (as in, the redacted file size is identical to the original).
I was able to open the trace in gotraceui again by applying this change:
diff --git a/trace/ptrace/ptrace.go b/trace/ptrace/ptrace.go
index 2d59937..e1c5c50 100644
--- a/trace/ptrace/ptrace.go
+++ b/trace/ptrace/ptrace.go
@@ -658,6 +658,9 @@ func processEvents(r *exptrace.Reader, tr *Trace, progress func(float64)) error
case rangeScopeUnknown:
continue
case rangeScopeGC:
+ if len(tr.GC) == 0 {
+ continue
+ }
prev = &tr.GC[len(tr.GC)-1]
case rangeScopeSTW:
prev = &tr.STW[len(tr.STW)-1]But I don't know if that is actually an appropriate fix, nor do I know enough about trace internals to say what's actually going on here.
Activity
dominikh commentedon Nov 25, 2025
Thanks for the reproducer. I'll try to look into it asap.
dominikh commentedon Dec 15, 2025
This has turned into a whole thing (golang/go#62627 (comment)) and a proper fix is waiting on changes to x/exp/trace.