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Regions

Schema:ethdebug/format/pointer/region→

A region represents a contiguous block of bytes in a specific EVM data location. Regions are the leaves of the pointer tree—the actual byte ranges that hold data.

To resolve regions against live EVM state interactively, see the Pointer playground.

Addressing schemes​

The EVM uses two different models for organizing bytes, and regions reflect this:

Slice-based locations​

Memory, calldata, returndata, and code are byte-addressable. Regions in these locations use offset and length:

  • offset: byte position from the start (required)
  • length: number of bytes (required)

Slot-based locations​

Storage, transient storage, and stack are organized in 32-byte slots. Regions use slot.

For storage and transient storage, values that don't fill a full slot can specify sub-slot positioning with offset and length within the slot — useful for packed storage, such as a 20-byte address held at byte 12 of a slot.

Location-specific details​

Memory​

Memory is a simple byte array that grows as needed. Memory addresses often come from the free memory pointer (stored at 0x40).

Storage​

Storage persists between transactions. Slots are 32-byte words addressed by 256-bit keys. Slot addresses can be literal numbers, hex strings, or computed expressions.

Stack​

The EVM stack holds up to 1024 words; slot 0 is the top. Stack regions are typically read-only from a debugging perspective—you observe values but don't address sub-ranges.

Calldata​

Function arguments arrive in calldata, read-only and byte-addressable. The first 4 bytes are typically the function selector; arguments follow.

Returndata​

After a call, the data it returned is accessible as a byte-addressable region.

Code​

Contract bytecode can be read as data. This is used for immutable variables and other data embedded in bytecode.

Transient storage​

Transient storage (EIP-1153) persists only within a transaction and uses the same slot-based addressing as regular storage.

Naming regions​

Any region can have a name that other parts of the pointer reference. Names enable:

  • Reading the region's value with { "$read": "token-balance" }
  • Referencing properties with { ".slot": "token-balance" }
  • Building self-documenting pointer structures

Dynamic addresses​

Region fields like offset, slot, and length can use expressions to compute values at runtime. This enables pointers for dynamic data like arrays and mappings.

For the full expression language including arithmetic, $keccak256, and value reading, see expressions.

Learn more​

For complete schemas for each location type, see the pointer region specification.