tetragon: ensure struct alignment on startup

Mismatches between the BPF and userspace API are often the cause of bizarre bugs that are
difficult to debug. This might happen if a developer makes a change to one and forgets to
update the other, or it might simply happen during development if the userspace and BPF
targets go out of sync. This PR introduces alignment checks to the Tetragon startup
process so that we can fail with a clear error message when such situations arise.

Signed-off-by: William Findlay <will@isovalent.com>

cmd/tetragon/main.go

@@ -11,6 +11,7 @@ import (
 	pprofhttp "net/http/pprof"
 	"os"
 	"os/signal"
+	"path"
 	"path/filepath"
 	"runtime"
 	"runtime/pprof"
@@ -20,6 +21,7 @@ import (
 	"time"
 
 	"github.com/cilium/tetragon/api/v1/tetragon"
+	"github.com/cilium/tetragon/pkg/alignchecker"
 	"github.com/cilium/tetragon/pkg/bpf"
 	"github.com/cilium/tetragon/pkg/btf"
 	"github.com/cilium/tetragon/pkg/bugtool"
@@ -72,6 +74,11 @@ var (
 	log = logger.GetLogger()
 )
 
+func checkStructAlignments() error {
+	path := path.Join(option.Config.HubbleLib, "bpf_alignchecker.o")
+	return alignchecker.CheckStructAlignments(path)
+}
+
 func getExportFilters() ([]*tetragon.Filter, []*tetragon.Filter, error) {
 	allowList, err := filters.ParseFilterList(viper.GetString(option.KeyExportAllowlist), viper.GetBool(option.KeyEnablePidSetFilter))
 	if err != nil {
@@ -178,6 +185,10 @@ func tetragonExecute() error {
 		defaults.NetnsDir = viper.GetString(option.KeyNetnsDir)
 	}
 
+	if err := checkStructAlignments(); err != nil {
+		return fmt.Errorf("struct alignment checks failed: %w", err)
+	}
+
 	checkprocfs.Check()
 
 	// Setup file system mounts