golang/go · error

error parsing profile: %w

Error message

error parsing profile: %w

What it means

The `preprofile` tool successfully opened the input pprof file but failed to parse it into a profile structure via `pgo.FromPProf`. This means the file exists and is readable but its contents are not a valid pprof-format profile, or the profile is structurally invalid for PGO purposes. The `pgo.FromPProf` function reads the protobuf-encoded pprof data and extracts function/weight information needed for profile-guided optimization.

Source

Thrown at src/cmd/preprofile/main.go:46

	os.Exit(2)
}

var (
	output = flag.String("o", "", "output file path")
	input  = flag.String("i", "", "input pprof file path")
)

func preprocess(profileFile string, outputFile string) error {
	f, err := os.Open(profileFile)
	if err != nil {
		return fmt.Errorf("error opening profile: %w", err)
	}
	defer f.Close()

	r := bufio.NewReader(f)
	d, err := pgo.FromPProf(r)
	if err != nil {
		return fmt.Errorf("error parsing profile: %w", err)
	}

	var out *os.File
	if outputFile == "" {
		out = os.Stdout
	} else {
		out, err = os.Create(outputFile)
		if err != nil {
			return fmt.Errorf("error creating output file: %w", err)
		}
		defer out.Close()
	}

	w := bufio.NewWriter(out)
	if _, err := d.WriteTo(w); err != nil {
		return fmt.Errorf("error writing output file: %w", err)
	}

View on GitHub (pinned to b6b368adc5)

Solutions

1. Verify the file is a valid pprof profile: `go tool pprof <file>` should open it without errors.
2. Ensure the profile is a CPU profile, not a heap/goroutine/mutex/block profile — PGO requires CPU profiles specifically.
3. Regenerate the profile from scratch: run a fresh CPU profiling session and save a new profile.
4. Check the profile file size — a very small file may indicate truncation; re-run profiling.
5. If using an old Go version to generate the profile and a newer version to consume it, regenerate with the current toolchain.

Example fix

# Before: using a non-CPU profile or corrupt file for PGO
go build -pgo=heap.prof ./...  # wrong profile type

# After: generate and use a valid CPU profile
# 1. Generate CPU profile
go test -cpuprofile=cpu.prof -bench=. ./...
# 2. Verify it's valid
go tool pprof -top cpu.prof
# 3. Use for PGO
go build -pgo=cpu.prof ./...

// Validate the profile is a parseable CPU pprof before using for PGO
p, err := profile.ParseFile(profilePath)
if err != nil {
    log.Fatalf("Invalid pprof file: %v", err)
}
// Verify it contains CPU samples
isCPU := false
for _, st := range p.SampleType {
    if st.Type == "cpu" || st.Type == "samples" {
        isCPU = true
    }
}
if !isCPU {
    log.Fatal("PGO requires a CPU profile, not %s", p.SampleType)
}

When it happens

Trigger: Fires at preprofile/main.go:44-46 when `pgo.FromPProf(r)` returns an error. The input is read via a `bufio.Reader` wrapping the file handle. This happens when the file is not valid protobuf, is truncated, or contains a valid pprof file but with missing/invalid fields required for PGO (e.g., no sample types, no function mappings).

Common situations: Pointing `-pgo` at a file that is not actually a pprof CPU profile (e.g., a heap profile, a text file, or a different binary format). The profile file was truncated due to a crash during profiling or an incomplete file transfer. Using a profile generated by an incompatible or very old version of the profiling tool. The protobuf data is corrupted. Passing a gzip-compressed file that isn't actually a pprof protobuf inside.

Related errors

• error opening profile: %w
• error creating output file: %w
• error writing output file: %w
• error processing pprof PGO profile: %w
• error parsing profile: %w

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/f29a895560003792. Report an issue: GitHub.