go-delve/delve · error

malformed delve header note: %q

Error message

malformed delve header note: %q

What it means

platformFromNotes parses the Delve header note embedded in a core dump, whose first line must be '<OS>/<arch>'. If the note type matches but the first line does not split into exactly two slash-separated parts, the note is considered malformed and this error is thrown instead of guessing the platform.

Source

Thrown at pkg/proc/core/delve_core.go:23

	"encoding/binary"
	"fmt"
	"strconv"
	"strings"

	"github.com/go-delve/delve/pkg/dwarf/op"
	"github.com/go-delve/delve/pkg/elfwriter"
	"github.com/go-delve/delve/pkg/proc"
)

func platformFromNotes(notes []*note) (goos, goarch string, err error) {
	for _, note := range notes {
		if note.Type != elfwriter.DelveHeaderNoteType {
			continue
		}
		lines := strings.Split(string(note.Desc.([]byte)), "\n")
		v := strings.Split(lines[0], "/")
		if len(v) != 2 {
			return "", "", fmt.Errorf("malformed delve header note: %q", string(note.Desc.([]byte)))
		}
		return v[0], v[1], nil
	}
	panic("internal error")
}

func threadsFromDelveNotes(p *process, notes []*note) (proc.Thread, error) {
	var currentThread proc.Thread
	for _, note := range notes {
		if note.Type == elfwriter.DelveHeaderNoteType {
			buf := bytes.NewBuffer(note.Desc.([]byte))
			for {
				line, err := buf.ReadString('\n')
				if err != nil {
					break
				}
				if len(line) > 0 && line[len(line)-1] == '\n' {
					line = line[:len(line)-1]

View on GitHub (pinned to a23773e6c3)

Solutions

1. Regenerate the core dump with an unmodified, matching version of delve (dlv core / dlv debug with core support).
2. Verify the note payload: the first line must be exactly 'GOOS/GOARCH', e.g. 'linux/amd64'.
3. Check for file truncation or corruption by comparing the core file size against the original.
4. If the core came from another tool, open it with the tool-appropriate debugger instead of delve.

Example fix

// before (malformed note written by custom tool)
desc := []byte("linux amd64") // no slash
// after (correct delve header note format)
desc := []byte("linux/amd64\n...")

// Inspect the delve header note before loading
parts := strings.SplitN(firstLine, "/", 2)
if len(parts) != 2 || parts[0] == "" || parts[1] == "" {
	return fmt.Errorf("note first line %q is not GOOS/GOARCH", firstLine)
}

func isWellFormedDelveHeader(desc []byte) bool {
	lines := strings.Split(string(desc), "\n")
	v := strings.Split(lines[0], "/")
	return len(v) == 2 && v[0] != "" && v[1] != ""
}

When it happens

Trigger: Calling readLinuxOrPlatformIndependentCore on a core file that contains a note with type elfwriter.DelveHeaderNoteType whose Desc payload's first line is not of the form 'linux/amd64' (e.g. no slash, or more than one slash).

Common situations: Core files produced by modified, hand-edited, or third-party tools that imitate the delve header note; truncated or corrupted note payloads; files written by a different delve version with a changed header format.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• malformed delve header note (bad pid): %v
• malformed delve header note (bad entry point): %v
• reading name: %v
• short read
• can not continue execution of core process

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/44b328ff17a80a49. Report an issue: GitHub.