oracle/graal · error · GraalError

Cannot bind label to negative position %d

Error message

Cannot bind label to negative position %d

What it means

Thrown by readPrimitiveArrayUnaligned when the array constant is not an EspressoExternalObjectConstant. The unaligned read decodes bytes directly from the guest array via interop buffer access (readBufferByte/Short/Int/Long/...), which requires an espresso object constant holding the polyglot Value.

Source

Thrown at compiler/src/jdk.graal.compiler/src/jdk/graal/compiler/asm/Label.java:78

    public Label() {
        blockId = -1;
    }

    public Label(int id) {
        blockId = id;
    }

    public int getBlockId() {
        return blockId;
    }

    /**
     * Binds the label to {@code pos} and patches all instructions added by
     * {@link #addPatchAt(int, Assembler)}.
     */
    protected void bind(int pos, Assembler<?> asm) {
        if (pos < 0) {
            throw new GraalError("Cannot bind label to negative position %d", pos);
        }
        this.position = pos;
        if (patchPositions != null) {
            for (int i = 0; i < patchPositions.size(); ++i) {
                asm.patchJumpTarget(patchPositions.get(i), position);
            }
            patchPositions = null;
        }
    }

    public boolean isBound() {
        return position >= 0;
    }

    public void addPatchAt(int branchLocation, Assembler<?> asm) {
        assert !isBound() : "Label is already bound " + this + " " + branchLocation + " at position " + position;
        if (patchPositions == null) {
            patchPositions = new ArrayList<>(2);

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Only pass espresso object constants obtained from the same vm access instance
2. Guard with instanceof and route non-espresso constants to the host unaligned read implementation

Example fix

// before
JavaConstant v = vmAccess.readPrimitiveArrayUnaligned(anyConst, kind, offset);

// after
JavaConstant v = anyConst instanceof EspressoExternalObjectConstant
        ? vmAccess.readPrimitiveArrayUnaligned(anyConst, kind, offset)
        : hostBackend.readUnaligned(anyConst, kind, offset);

static boolean isEspressoObjectConstant(JavaConstant c) {
    return c instanceof EspressoExternalObjectConstant;
}

When it happens

Trigger: Passing a host constant, primitive constant, or foreign-backend constant as the array argument.

Common situations: Constants crossing backend boundaries (host JVMCI -> espresso access); mocks; stale constants from a previous guest context.

Related errors

• Out of scratch registers: %s
• Branch target %d out of bounds
• Expected an espresso object constant, got {}
• Expected an espresso object receiver, got {}
• Expected value kind {} but got {}

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/f2675dc4fe9b743c. Report an issue: GitHub.