oracle/graal · error · IllegalArgumentException

Unrecognized unit prefix: {size} use `T`, `G`, `M`, or `k`.

Error message

Unrecognized unit prefix: {size} use `T`, `G`, `M`, or `k`.

What it means

The final switch of the size converter accepts only T/t, G/g, M/m, K/k as the single unit character. Any other character after the digits (e.g. 'B', 'b', 'i') falls to default and throws, advising the four supported prefixes.

Source

Thrown at espresso/src/com.oracle.truffle.espresso/src/com/oracle/truffle/espresso/EspressoOptions.java:584

            long result = Long.parseLong(size.substring(0, idx));

            if (idx < len) {
                switch (size.charAt(idx)) {
                    case 'T': // fallthrough
                    case 't':
                        return result * K * K * K * K;
                    case 'G': // fallthrough
                    case 'g':
                        return result * K * K * K;
                    case 'M': // fallthrough
                    case 'm':
                        return result * K * K;
                    case 'K': // fallthrough
                    case 'k':
                        return result * K;
                    default:
                        throw new IllegalArgumentException("Unrecognized unit prefix: " + size + " use `T`, `G`, `M`, or `k`.");
                }
            }
            return result;

        }
    });

    @Option(help = "Maximum total size of NIO direct-buffer allocations.", //
                    category = OptionCategory.EXPERT, //
                    stability = OptionStability.STABLE, usageSyntax = "<size>[<unit>]") //
    public static final OptionKey<Long> MaxDirectMemorySize = new OptionKey<>(-1L, SIZE_OPTION_TYPE);

    @Option(help = "Load native agents from standard library paths. \\n" +
                    "Keys represent the agent library name, values are the corresponding agent options.\\n" +
                    "Agents are not fully implemented yet.", //
                    category = OptionCategory.INTERNAL, //
                    stability = OptionStability.EXPERIMENTAL, //
                    usageSyntax = "<agentOptions>") //

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Use T, G, M, or k (case-insensitive) as the unit.
2. For plain bytes, omit the unit entirely.
3. Beware that 'b' is NOT accepted - use no unit for bytes.

Example fix

# before
--java.MaxDirectMemorySize=16B

# after
--java.MaxDirectMemorySize=16   # bytes, no unit

if (!size.matches("\\d+([TtGgMmKk])?")) throw new ConfigException("Unit must be T/G/M/k: " + size);

static boolean validUnit(String s) { return s != null && s.matches("\\d+[TtGgMmKk]?"); }

When it happens

Trigger: --java.MaxDirectMemorySize=16B, 1b, or 1x - the value starts with digits and has exactly one trailing character, but that character is not T/G/M/K.

Common situations: Writing '16B' for bytes (use a plain number instead); binary-unit 'i' from GiB notation; typos.

Related errors

• Not starting with digits: {size}
• Unit prefix can be at most one character: {size}
• --java.SpecCompliance: Mode can be 'strict' or 'hotspot'.
• -Xverify: Mode can be 'none', 'remote' or 'all'.
• --java.LivenessAnalysis can only be 'none'|'false', 'auto' o

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/04de453703b49d79. Report an issue: GitHub.