golang/go · error

%s: %v; output: %q

Error message

%s: %v; output: %q

What it means

gccToolIDPrefix runs '<name> -### -x <language> -c -' (e.g. 'gcc -### -x c -c -') to capture the driver's expanded subcommands and version string. If cmd.CombinedOutput returns an error (binary missing, non-zero exit, signal), the error is wrapped with the binary name and the raw output for diagnosis.

Source

Thrown at src/cmd/go/internal/work/buildid.go:246

	b.id.Lock()
	id = b.gccToolIDCache[key]
	exe = b.gccToolIDCache[key+".exe"]
	b.id.Unlock()

	if id != "" {
		return id, exe, nil
	}

	// Invoke the driver with -### to see the subcommands and the
	// version strings. Use -x to set the language. Pretend to
	// compile an empty file on standard input.
	cmdline := str.StringList(prefix, name, "-###", "-x", language, "-c", "-")
	cmd := exec.Command(cmdline[0], cmdline[1:]...)
	// Force untranslated output so that we see the string "version".
	cmd.Env = append(os.Environ(), "LC_ALL=C")
	out, err := cmd.CombinedOutput()
	if err != nil {
		return "", "", fmt.Errorf("%s: %v; output: %q", name, err, out)
	}

	version := ""
	lines := strings.Split(string(out), "\n")
	for _, line := range lines {
		fields := strings.Fields(line)
		for i, field := range fields {
			if strings.HasSuffix(field, ":") {
				// Avoid parsing fields of lines like "Configured with: …", which may
				// contain arbitrary substrings.
				break
			}
			if field == "version" && i < len(fields)-1 {
				// Check that the next field is plausibly a version number.
				// We require only that it begins with an ASCII digit,
				// since we don't know what version numbering schemes a given
				// C compiler may use. (Clang and GCC mostly seem to follow the scheme X.Y.Z,
				// but in https://go.dev/issue/64619 we saw "8.3 [DragonFly]", and who knows

View on GitHub (pinned to b6b368adc5)

Solutions

1. Verify the compiler exists: 'which gcc' / 'which gccgo' (or the value of CC/GCCGO).
2. Install the missing compiler (e.g. 'apt install gcc' or 'apt install gccgo').
3. Set CC=/full/path/to/gcc or GCCGO=/full/path/to/gccgo explicitly.
4. Inspect the captured output in the error for the real failure (missing cc1, permission denied, etc.).

Example fix

// before
$ CC=clang-99 go build ./...
// error: clang-99: exec: "clang-99": executable file not found in $PATH; output: ""

// after
$ which clang
/usr/bin/clang
$ CC=/usr/bin/clang go build ./...

// Confirm the configured C/gccgo compiler is invocable.
func checkCompiler(name string) error {
    lp, err := exec.LookPath(name)
    if err != nil { return fmt.Errorf("compiler %q not on PATH", name) }
    cmd := exec.Command(lp, "-###", "-x", "c", "-c", "-")
    cmd.Env = append(os.Environ(), "LC_ALL=C")
    if out, err := cmd.CombinedOutput(); err != nil {
        return fmt.Errorf("%s invocation failed: %v; output: %q", lp, err, out)
    }
    return nil
}

When it happens

Trigger: Building with cgo or gccgo where the configured C/gccgo compiler (CC, GCCGO, or auto-detected) doesn't exist on PATH, isn't executable, or crashes when invoked with -###. Also triggered by a compiler that emits to stderr and exits non-zero.

Common situations: CC points at a missing binary after a toolchain uninstall; cross-compile environments where the cross-gcc isn't installed; a misconfigured GCCGO env var; clang invoked with flags gcc expects.

Related errors

• %s: can not find version number in %q
• %s: can not find compilation command in %q
• %s: compilation command confusion %q
• C compiler %q not found: %v
• Fortran source files not allowed when not using cgo or SWIG:

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/6f7c7175ce7df233. Report an issue: GitHub.