fix(bpfassets): Fix object file lookup (#1419)

For local development the instructions suggest running:

./_output/bin/linux_amd64/kepler

This checks for the bytecode in /var/lib/kepler/bpfassets
However, for local development this directory doesn't exist.

The fallback was to look in ../../../bpfassets/libbpf/bpf.o
Running the recommended command was causing kepler to look in
strange locations (i.e /bpfassets) for bytecode.

This PR fixes the lookup for local development to use a glob
pattern starting at the current directory. This works well
for local development, with the added bonus of making it easier
to test kepler builds on remote systems since you can also
copy the binary and bytecode files together, without having
to place the bytecode in a special path.

Signed-off-by: Dave Tucker <[email protected]>

pkg/bpfassets/attacher/attacher.go

@@ -39,15 +39,14 @@ import (
 )
 
 const (
-	objectFilename       = "kepler.%s.o"
-	bpfAssesstsLocation  = "/var/lib/kepler/bpfassets"
-	bpfAssesstsLocalPath = "../../../bpfassets/libbpf/bpf.o"
-	cpuOnline            = "/sys/devices/system/cpu/online"
-	CPUCycleLabel        = config.CPUCycle
-	CPURefCycleLabel     = config.CPURefCycle
-	CPUInstructionLabel  = config.CPUInstruction
-	CacheMissLabel       = config.CacheMiss
-	TaskClockLabel       = config.TaskClock
+	objectFilename      = "kepler.%s.o"
+	bpfAssestsLocation  = "/var/lib/kepler/bpfassets"
+	cpuOnline           = "/sys/devices/system/cpu/online"
+	CPUCycleLabel       = config.CPUCycle
+	CPURefCycleLabel    = config.CPURefCycle
+	CPUInstructionLabel = config.CPUInstruction
+	CacheMissLabel      = config.CacheMiss
+	TaskClockLabel      = config.TaskClock
 
 	// Per /sys/kernel/debug/tracing/events/irq/softirq_entry/format
 	// { 0, "HI" }, { 1, "TIMER" }, { 2, "NET_TX" }, { 3, "NET_RX" }, { 4, "BLOCK" }, { 5, "IRQ_POLL" }, { 6, "TASKLET" }, { 7, "SCHED" }, { 8, "HRTIMER" }, { 9, "RCU" }
@@ -149,20 +148,27 @@ func getLibbpfObjectFilePath() (string, error) {
 		endianness = "bpfeb"
 	}
 	filename := fmt.Sprintf(objectFilename, endianness)
-	bpfassetsPath := fmt.Sprintf("%s/%s", bpfAssesstsLocation, filename)
+	bpfassetsPath := fmt.Sprintf("%s/%s", bpfAssestsLocation, filename)
 	_, err := os.Stat(bpfassetsPath)
 	if err != nil {
-		var absPath string
-		// try relative path
-		absPath, err = filepath.Abs(bpfAssesstsLocalPath)
+		// attempt to find the bpf assets in the same directory as the binary
+		// this is useful for running locally
+		var matches []string
+		err = filepath.Walk(".", func(path string, info os.FileInfo, err error) error {
+			if info.Name() == filename {
+				matches = append(matches, path)
+				return filepath.SkipAll
+			}
+			return nil
+		})
 		if err != nil {
-			return "", err
+			return "", fmt.Errorf("failed to find bpf object file: %v", err)
 		}
-		bpfassetsPath = fmt.Sprintf("%s/%s", absPath, filename)
-		_, err = os.Stat(bpfassetsPath)
-		if err != nil {
-			return "", err
+		if len(matches) < 1 {
+			return "", fmt.Errorf("failed to find bpf object file: no matches found")
 		}
+		klog.Infof("found bpf object file: %s", matches[0])
+		return matches[0], nil
 	}
 	return bpfassetsPath, nil
 }
@@ -187,12 +193,15 @@ func attachLibbpfModule() (*bpf.Module, error) {
 	}()
 	var libbpfObjectFilePath string
 	libbpfObjectFilePath, err = getLibbpfObjectFilePath()
-	if err == nil {
-		libbpfModule, err = bpf.NewModuleFromFile(libbpfObjectFilePath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to find ebpf bytecode: %v", err)
 	}
+
+	libbpfModule, err = bpf.NewModuleFromFile(libbpfObjectFilePath)
 	if err != nil {
-		return nil, fmt.Errorf("failed to load module: %v", err)
+		return nil, fmt.Errorf("failed to load eBPF module from libbpf object: %v", err)
 	}
+
 	// resize array entries
 	klog.Infof("%d CPU cores detected. Resizing eBPF Perf Event Arrays", cpuCores)
 	for _, arrayName := range bpfArrays {