What causes "Failed to allocate block: " + blockName" in NationalSecurityAgency/ghidra?

Reduce the requested extBlockSize or relocate to an address space with more free room.

NationalSecurityAgency/ghidra · error · MemoryAccessException

Failed to allocate block: " + blockName

Error message

Failed to allocate block: " + blockName

What it means

Thrown as MemoryAccessException from the ext-block allocation helper when startAddr is still null after scanning the address space for a gap large enough to hold the uninitialized block. The loop tried successive offsets looking for a free region of extBlockSize; none was found, so createUninitializedBlock could not be called.

Source

Thrown at Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/analysis/MingwRelocationAnalyzer.java:868

		for (long offset = delta; offset < 0x100000000L; offset += delta) {
			Address addr = space.getAddress(offset);
			AddressIterator addresses = memory.getAddresses(addr, true);
			if (!addresses.hasNext()) {
				startAddr = addr;
				break;
			}
			Address nextAddr = addresses.next();
			if (!nextAddr.getAddressSpace().equals(space) ||
				nextAddr.subtract(addr) > extBlockSize) {
				startAddr = addr;
				break;
			}
		}
		if (startAddr != null) {
			memory.createUninitializedBlock(blockName, startAddr, extBlockSize, false);
			return startAddr;
		}
		throw new MemoryAccessException("Failed to allocate block: " + blockName);
	}

	private boolean relocateV1(Address pdwListPayloadAddr, int entryCount, MessageLog log,
			TaskMonitor monitor) throws CancelledException {

		Listing listing = program.getListing();
		Data d = listing.getDefinedDataAt(pdwListPayloadAddr);
		if (d != null && (d.isArray() || d.isStructure())) {
			return false; // silent - appears to have been previously processed
		}

		Memory memory = program.getMemory();
		DataTypeManager dtm = program.getDataTypeManager();
		RelocationTable relocationTable = program.getRelocationTable();

		Address addr = pdwListPayloadAddr;
		DumbMemBufferImpl buf = new DumbMemBufferImpl(memory, pdwListPayloadAddr);

View on GitHub (pinned to d5f144c24d)

Solutions

Reduce the requested extBlockSize or relocate to an address space with more free room.
Free/clear overlapping blocks in the target region before allocating.
Run the analyzer earlier in the pipeline before other analyzers consume the available gaps.
Catch MemoryAccessException and skip ext-block relocation handling for this binary.

Example fix

// before — throws when no gap is found
Address start = allocateExtBlock(space, extBlockSize, blockName);

// after — scan a wider range or fall back to overlay space
Address start = findGap(space, extBlockSize, 0x100000000L, 0x200000000L);
if (start == null) {
    // fall back to an overlay address space
    AddressSpace overlay = program.getAddressFactory().getAddressSpace("overlay");
    start = overlay.getAddress(extBlockSize);
}
if (start == null) {
    throw new MemoryAccessException("Failed to allocate block: " + blockName);
}

Defensive patterns

Strategy: try-catch

Validate before calling

// probe for a free gap before attempting allocation
Address gap = findGap(space, extBlockSize, 0L, 0x100000000L);
if (gap == null) {
    // no room — skip ext-block allocation
}

Type guard

boolean hasGap = findGap(space, extBlockSize, 0L, 0x100000000L) != null;

Try / catch

try {
    allocateExtBlock(space, extBlockSize, blockName);
} catch (MemoryAccessException e) {
    log.appendMsg("No room for " + blockName + ": " + e.getMessage());
}

Prevention

Run the analyzer before others consume address-space gaps.
Reduce extBlockSize when relocation metadata is mis-parsed as huge.
Clear overlapping blocks in the target region before allocating.

When it happens

Trigger: The scan over the address space (offset from delta up to 0x100000000L in steps of delta) never finds a gap where the next address is in a different space or far enough away — i.e. memory is fully populated/fragmented with no room for an extBlockSize uninitialized block.

Common situations: Analyzing a large or densely-mapped binary where the relevant address space has no contiguous free region of the required size; an extBlockSize that is unexpectedly large due to mis-parsed relocation metadata; running on a program whose image base leaves little headroom.

Related errors

AI-assisted analysis of NationalSecurityAgency/ghidra@d5f144c24d (2026-08-14). Data as JSON: /api/errors/b7d223a7bfdd8b1b. Report an issue: GitHub.