Add -version flag to print version info (#13)

* Add -version flag to print version

* add go version

gmon.sh

@@ -30,6 +30,7 @@ dockerfile_buildenv=$(mktemp)
 cat > "$dockerfile_buildenv" <<EOF
 FROM debian:bookworm-20240513@sha256:fac2c0fd33e88dfd3bc88a872cfb78dcb167e74af6162d31724df69e482f886c
 RUN apt-get update && apt-get install -y --no-install-recommends \
+ git \
  wget \
  llvm-14 \
  clang-14 \
@@ -54,9 +55,12 @@ docker run --platform linux/$arch -i \
 -e BPF_CLANG="clang" \
 -e BPF_CFLAGS="-O2 -g -Wall -Werror" \
 --rm $image_buildenv bash -c '\
+ git config --global --add safe.directory /usr/src && \
  bpftool btf dump file /sys/kernel/btf/vmlinux format c > ./ebpf/c/vmlinux.h && \
  go generate -x ./... && \
- GOFLAGS="-buildvcs=false" CGO_ENABLED=0 go build -o /usr/src/bin/gmon'
+ GOFLAGS="-buildvcs=auto" CGO_ENABLED=0 go build \
+ -ldflags "-s -w -X main.Version=0.0.0-dev" \
+ -o /usr/src/bin/gmon'
 if [ "$1" = "build" ]; then
  exit 0
 fi

main.go

@@ -14,6 +14,7 @@ import (
  "os"
  "os/signal"
  "runtime"
+ "runtime/debug"
  "runtime/trace"
  "strings"
 
@@ -45,6 +46,10 @@ var (
  traceOutPath = flag.String("trace", "", "Path to Go runtime/trace output")
  pprofPort = flag.Int("pprof", 0, "Port to be used for pprof server. If 0, pprof server is not started")
  metricsPort = flag.Int("metrics", 5500, "Port to be used for metrics server, /metrics endpoint")
+ printVersion = flag.Bool("version", false, "Print version information")
+
+ // Set by -ldflags at build time
+ Version = "unknown"
 )
 
 type promLogger struct{}
@@ -55,6 +60,25 @@ func (promLogger) Println(v ...interface{}) {
 
 func main() {
  flag.Parse()
+ if *printVersion {
+ var gover, arch, goos, commitHash = "unknown", "unknown", "unknown", "unknown"
+ if info, ok := debug.ReadBuildInfo(); ok {
+ gover = info.GoVersion
+ for _, s := range info.Settings {
+ switch s.Key {
+ case "GOARCH":
+ arch = s.Value
+ case "GOOS":
+ goos = s.Value
+ case "vcs.revision":
+ commitHash = s.Value
+ }
+ }
+ }
+ fmt.Printf("gmon %s (%s/%s) %s, commit=%s\n", Version, goos, arch, gover, commitHash)
+ return
+ }
+
  opts := &slog.HandlerOptions{Level: levelMap[*level]}
  slog.SetDefault(slog.New(slog.NewTextHandler(os.Stdout, opts)))
  errlog := log.New(os.Stderr, "", log.LstdFlags)