runtime/trace: disable frame pointer unwinding on plan9

Fixes #60254

Change-Id: Ifd9e517a9479e5cd63fd3622b2556989d5f84eb9
Reviewed-on: https://go-review.googlesource.com/c/go/+/499036
Reviewed-by: Austin Clements <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Run-TryBot: Keith Randall <[email protected]>
TryBot-Bypass: Keith Randall <[email protected]>

Author: psilva261

src/runtime/trace.go

@@ -15,6 +15,7 @@ package runtime
 import (
 	"internal/abi"
 	"internal/goarch"
+	"internal/goos"
 	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
@@ -993,8 +994,9 @@ func traceStackID(mp *m, pcBuf []uintptr, skip int) uint64 {
 
 // tracefpunwindoff returns true if frame pointer unwinding for the tracer is
 // disabled via GODEBUG or not supported by the architecture.
+// TODO(#60254): support frame pointer unwinding on plan9/amd64.
 func tracefpunwindoff() bool {
-	return debug.tracefpunwindoff != 0 || (goarch.ArchFamily != goarch.AMD64 && goarch.ArchFamily != goarch.ARM64)
+	return debug.tracefpunwindoff != 0 || (goarch.ArchFamily != goarch.AMD64 && goarch.ArchFamily != goarch.ARM64) || goos.IsPlan9 == 1
 }
 
 // fpTracebackPCs populates pcBuf with the return addresses for each frame and