skylot/jadx · error · JadxRuntimeException

Incorrect negative register number in instruction: {}

Error message

Incorrect negative register number in instruction: {}

What it means

Thrown by CheckCode.checkInstructions() when iterating every register referenced by an instruction and finding one whose register number is negative. Register numbers must be non-negative integers in valid Dalvik bytecode; a negative value indicates the instruction was built incorrectly during earlier decoding or that the DEX file is corrupt.

Source

Thrown at jadx-core/src/main/java/jadx/core/dex/visitors/CheckCode.java:76

		if (isEmpty(mth.getInstructions())) {
			return;
		}
		int regsCount = mth.getRegsCount();
		List<RegisterArg> list = new ArrayList<>();
		for (InsnNode insnNode : mth.getInstructions()) {
			if (insnNode == null) {
				continue;
			}
			list.clear();
			RegisterArg resultArg = insnNode.getResult();
			if (resultArg != null) {
				list.add(resultArg);
			}
			insnNode.getRegisterArgs(list);
			for (RegisterArg arg : list) {
				int regNum = arg.getRegNum();
				if (regNum < 0) {
					throw new JadxRuntimeException("Incorrect negative register number in instruction: " + insnNode);
				}
				if (regNum >= regsCount) {
					throw new JadxRuntimeException("Incorrect register number in instruction: " + insnNode
							+ ", expected to be less than " + regsCount);
				}
			}
		}
	}
}

View on GitHub (pinned to e738a26571)

Solutions

Upgrade jadx — instruction decoding and register handling are regularly fixed.
Catch JadxRuntimeException around per-class decompilation to avoid aborting the whole batch.
Report the issue with the instruction dump from the error message and the offending DEX.
If the DEX is corrupt, re-verify with dexdump or baksmali and obtain a non-corrupt copy.

Defensive patterns

Strategy: try-catch

Validate before calling

// Basic DEX integrity sanity check before decompiling
import java.io.File;
import java.io.FileInputStream;

boolean looksLikeValidDex(File f) throws IOException {
    try (FileInputStream fis = new FileInputStream(f)) {
        byte[] magic = new byte[8];
        if (fis.read(magic) < 8) return false;
        // DEX magic: 'dex\n' followed by version and '\0'
        return magic[0] == 'd' && magic[1] == 'e' && magic[2] == 'x' && magic[3] == '\n';
    }
}

Try / catch

try {
    jadx.load();
    jadx.save();
} catch (JadxRuntimeException e) {
    // Catch at the batch level; consider per-class fallback
    LOG.error("Decompilation failed (register validation): {}", e.getMessage());
}

Prevention

Validate input DEX files with dexdump --verify before decompiling.
Use original APKs/DEX from trusted build tools; avoid re-processed or tampered files.
Upgrade jadx for instruction-decoder fixes.
Process per-class with try-catch to isolate corrupt methods.

When it happens

Trigger: CheckCode.visit() runs on a MethodNode, iterates mth.getInstructions(), collects result + source register args, and for some RegisterArg arg.getRegNum() < 0. This can happen if a register arg was created with an unset/default register number, or if a bytecode rewriter emitted an instruction with a malformed register operand.

Common situations: Corrupt or tampered DEX files, DEX produced by non-standard tools, or edge cases where jadx's own instruction decoder mis-parses a register slot. Rare with output from standard Android build tools (d8/r8).

Related errors

AI-assisted analysis of skylot/jadx@e738a26571 (2026-08-14). Data as JSON: /api/errors/54812d1c804f3fc1. Report an issue: GitHub.