runtime: add GODEBUG=tracebacklabels=1 to include pprof labels in tracebacks

Copy LabelSet to an internal package as label.Set, and include (escaped)
labels within goroutine stack dumps.

Labels are added to the goroutine header as quoted key:value pairs, so
the line may get long if there are a lot of labels.

To handle escaping, we add a printescaped function to the
runtime and hook it up to the print function in the compiler with a new
runtime.quoted type that's a sibling to runtime.hex. (in fact, we
leverage some of the machinery from printhex to generate escape
sequences).

The escaping can be improved for printable runes outside basic ASCII
(particularly for languages using non-latin stripts). Additionally,
invalid UTF-8 can be improved.

So we can experiment with the output format make this opt-in via a
a new tracebacklabels GODEBUG var.

Updates #23458
Updates #76349

Change-Id: I08e78a40c55839a809236fff593ef2090c13c036
Reviewed-on: https://go-review.googlesource.com/c/go/+/694119
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/runtime/export_test.go b/src/runtime/export_test.go
index 6e0360aaca..26341c4300 100644
--- a/src/runtime/export_test.go
+++ b/src/runtime/export_test.go
@@ -2064,3 +2064,15 @@ func HexdumpWords(p, bytes uintptr) string {
 	}
 	return string(buf[:n])
 }
+
+// DumpPrintQuoted provides access to print(quoted()) for the tests in
+// runtime/print_quoted_test.go, allowing us to test that implementation.
+func DumpPrintQuoted(s string) string {
+	gp := getg()
+	gp.writebuf = make([]byte, 0, 1<<20)
+	print(quoted(s))
+	buf := gp.writebuf
+	gp.writebuf = nil
+
+	return string(buf)
+}