golang/go · error

preprocessed profile entry got %v want 2 fields

Error message

preprocessed profile entry got %v want 2 fields

What it means

Thrown when the third line of a preprocessed PGO profile edge entry (the weight line) does not split into exactly 2 space-separated fields. The deserializer expects "<call-site-offset> <weight>" but strings.Split produced a different count — meaning the line has extra spaces, missing a field, or has a different delimiter.

Source

Thrown at src/cmd/internal/pgo/deserialize.go:72

			if err := scanner.Err(); err != nil {
				return nil, fmt.Errorf("error reading preprocessed profile: %w", err)
			}
			return nil, fmt.Errorf("preprocessed profile entry missing callee")
		}
		calleeName := scanner.Text()

		if !scanner.Scan() {
			if err := scanner.Err(); err != nil {
				return nil, fmt.Errorf("error reading preprocessed profile: %w", err)
			}
			return nil, fmt.Errorf("preprocessed profile entry missing weight")
		}
		readStr = scanner.Text()

		split := strings.Split(readStr, " ")

		if len(split) != 2 {
			return nil, fmt.Errorf("preprocessed profile entry got %v want 2 fields", split)
		}

		co, err := strconv.Atoi(split[0])
		if err != nil {
			return nil, fmt.Errorf("preprocessed profile error processing call line: %w", err)
		}

		edge := NamedCallEdge{
			CallerName:     callerName,
			CalleeName:     calleeName,
			CallSiteOffset: co,
		}

		weight, err := strconv.ParseInt(split[1], 10, 64)
		if err != nil {
			return nil, fmt.Errorf("preprocessed profile error processing call weight: %w", err)
		}

View on GitHub (pinned to b6b368adc5)

Solutions

1. Regenerate the profile with the matching Go toolchain to ensure the exact "offset weight" space-separated format.
2. Inspect the raw weight line bytes for tabs, multiple spaces, or missing fields and fix the serialization.
3. Ensure no editor or CI step reflows whitespace in the profile file.

Example fix

// The weight line must be exactly: "<int> <int>"
// Before (broken): "42  1000" (double space -> 3 fields after split)
// After (fixed):  "42 1000"

// Pre-validate that every third line has exactly 2 space-separated fields:
func validateWeightLines(path string) error {
    data, err := os.ReadFile(path)
    if err != nil { return err }
    lines := strings.Split(strings.TrimRight(string(data), "\n"), "\n")
    for i := 2; i < len(lines); i += 3 {
        fields := strings.Split(lines[i], " ")
        if len(fields) != 2 {
            return fmt.Errorf("line %d: expected 2 fields, got %d", i+1, len(fields))
        }
    }
    return nil
}

When it happens

Trigger: strings.Split(readStr, " ") on the weight line yields a slice whose length is not 2. This happens when the line has zero spaces (single field), multiple spaces (3+ fields after split), leading/trailing spaces, or uses a different separator like a tab.

Common situations: Profile serialized by a tool that used tab separators instead of spaces, or a tool that emitted extra metadata fields on the weight line. Also occurs if the file was reformatted or had whitespace stripped/added by an editor or version-control system.

Related errors

• preprocessed profile entry missing weight
• preprocessed profile error processing call line: %w
• preprocessed profile error processing call weight: %w
• preprocessed profile contains duplicate edge %+v
• error parsing profile: %w

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/4cc53af63b761055. Report an issue: GitHub.