runtime: avoid unsafe.{Slice,String} in debuglog

CL 428157 and CL 428759 switched debuglog to using unsafe.String and
unsafe.Slice, which broke the build with -tags=debuglog because this is
a no write barrier context, but runtime.unsafeString and unsafeSlice can
panic, which includes write barriers.

We could add a panicCheck1 path to these functions to reallow write
barriers, but it is a big mess to pass around the caller PC,
particularly since the compiler generates calls. It is much simpler to
just avoid unsafe.String and Slice.

Also add a basic test to build the runtime with -tags=debuglog to help
avoid future regressions.

For #54854.

Change-Id: I702418b986fbf189664e9aa4f40bc7de4d9e7781
Reviewed-on: https://go-review.googlesource.com/c/go/+/443380
Run-TryBot: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/runtime/debuglog_test.go b/src/runtime/debuglog_test.go
index 10dc72cf51..18c54a81b9 100644
--- a/src/runtime/debuglog_test.go
+++ b/src/runtime/debuglog_test.go
@@ -24,6 +24,7 @@ package runtime_test
 
 import (
 	"fmt"
+	"internal/testenv"
 	"regexp"
 	"runtime"
 	"strings"
@@ -155,3 +156,14 @@ func TestDebugLogLongString(t *testing.T) {
 		t.Fatalf("want %q, got %q", want, got)
 	}
 }
+
+// TestDebugLogBuild verifies that the runtime builds with -tags=debuglog.
+func TestDebugLogBuild(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// It doesn't matter which program we build, anything will rebuild the
+	// runtime.
+	if _, err := buildTestProg(t, "testprog", "-tags=debuglog"); err != nil {
+		t.Fatal(err)
+	}
+}