What causes "Failed: %s" in NationalSecurityAgency/ghidra?

Verify the input is an Itanium-ABI mangled C++ name (leading _Z) before invoking the demangler.

Failed: %s

Error message

Failed: %s

What it means

The non-IN_GLIBCPP_V3 standalone-demangler path: each command-line argument is passed to cplus_demangle_v3(argv[i], options); when it returns NULL the program prints 'Failed: <input>' to stderr and moves on. Unlike the GLIBCPP variant it does not report a status code (that API does not surface one), so the message is a pure 'could not demangle' diagnostic. The process still returns 0.

Source

Thrown at GPL/DemanglerGnu/src/demangler_gnu_v2_24/c/cp-demangle.c:5979

	  /* Attempt to demangle.  */
#ifdef IN_GLIBCPP_V3
	  s = __cxa_demangle (argv[i], NULL, NULL, &status);
#else
	  s = cplus_demangle_v3 (argv[i], options);
#endif

	  /* If it worked, print the demangled name.  */
	  if (s != NULL)
	    {
	      printf ("%s\n", s);
	      free (s);
	    }
	  else
	    {
#ifdef IN_GLIBCPP_V3
	      fprintf (stderr, "Failed: %s (status %d)\n", argv[i], status);
#else
	      fprintf (stderr, "Failed: %s\n", argv[i]);
#endif
	    }
	}
    }

  return 0;
}

#endif /* STANDALONE_DEMANGLER */

View on GitHub (pinned to d5f144c24d)

Solutions

Verify the input is an Itanium-ABI mangled C++ name (leading _Z) before invoking the demangler.
Check the -s style and demangling options match the input's ABI/compiler.
Use a demangler version matching the producing compiler to avoid ABI skew.
Filter non-mangled tokens out of the batch so expected failures do not flood output.

Example fix

# before
$ demangler _Z3foov plain_name
Failed: plain_name

# after - only feed mangled names
$ printf '%s\n' _Z3foov | demangler
foo()

Defensive patterns

Strategy: validation

Validate before calling

// Pre-filter to Itanium-ABI mangled names before invoking the standalone demangler
#include <string.h>
int looksMangled(const char *s) { return s && s[0] == '_' && s[1] == 'Z'; }
if (looksMangled(tok)) demangle_it(tok);
else fputs(tok, stdout); /* pass through unchanged */

Type guard

boolean looksLikeItaniumMangled(String s) {
    return s != null && s.startsWith("_Z");
}

Try / catch

// Standalone tool still returns 0; detect via stderr text.
if (rc == 0 && stderr_contains("Failed:")) {
    /* one or more tokens were not valid mangled names; expected for mixed input */
}

Prevention

Filter to plausible mangled names (leading _Z) before demangling.
Use a demangler version matching the producing compiler.
Confirm the -s style matches the input's ABI.
In batch runs, treat non-C++ tokens as expected failures.

When it happens

Trigger: Running the standalone demangler on a token that cplus_demangle_v3 rejects (returns NULL) - i.e. not a valid Itanium C++ mangled name given the selected options/style.

Common situations: Passing non-C++ symbols, already-demangled names, or malformed/truncated mangled names; selecting a demangling style (-s) incompatible with the input; using a demangler built for a different ABI than the compiler that produced the symbols.

Related errors

AI-assisted analysis of NationalSecurityAgency/ghidra@d5f144c24d (2026-08-14). Data as JSON: /api/errors/9629a0f09c3d6bf5. Report an issue: GitHub.