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4. Program storage and startup
4.1 Program objects
Every owned aggregate object and every top-level scalar variable has a fixed address and program lifetime. Aggregate fields and array elements occupy their containing object's storage. Aggregate constants are complete objects in the generated read-only-data region. Routine activations contain no owned aggregate object.
The compiler determines every program object's address, type, extent, and initial bytes before it commits the generated object. It retains initialized data length, aggregate-constant length, total read-only-data length, and BSS length as separate words. A constant symbol retains an offset relative to the aggregate-constant image, so later initialized declarations cannot change its identity. The compiler must reject a layout whose mathematical end exceeds the selected region.
4.2 Transcript barrier and image layout
The compiler reads the source stream once. Parsing and checking finish before the backend consumes the private semantic transcript, and that transcript is consumed once. The parser finalizes the initialized-data, BSS, and per-bank aggregate-constant used lengths before the backend emits any image record. Startup and selected-runtime lengths are also known. Startup copy and clear lengths, aggregate-constant addresses, each code base, and the ROM-mode copy source therefore require no fixup. Forward code addresses, including main, may use placeholder bytes followed by patch records under Section 9.2.
In a flat image, startup begins at imageBase, the selected runtime follows the startup stub, generated read-only bytes follow the runtime, and generated code follows the read-only extent. In ROM mode the read-only bytes contain the complete initialized-RAM load image followed by aggregate-constant bytes. In loaded mode initialized bytes occupy their runtime addresses within the image, and the generated read-only extent contains only aggregate constants.
Every bank reserves three bytes at bankWindowBase. The entry bank emits JP startup there; the other banks leave the slot to host image fill. The complete selected runtime begins at bankWindowBase + 3 in every bank. In the entry bank, startup follows that runtime, generated read-only data follows startup, and generated code follows the read-only extent. In every other bank, read-only data follows the runtime and precedes code. Only the entry bank contains startup and the initialized-RAM load image. The runtime identity fixes the canonical source, link rules, linked length, helper offsets, and RAM vector layout; this version performs no helper subsetting. Banks with the same complete link context use byte-identical linked helper images.
The initialized block begins with the adapter-selected runtime vector table, continues with the identity-fixed writable runtime state, and then contains source-declared initialized variables. The adapter contributes the vector and runtime-state bytes at contract-defined offsets; they are not Nucleus initializers. BSS follows the complete used initialized length.
The operating-layer runtime provider emits each complete, fully linked helper image at the derived runtime base. The compiler advances the corresponding target cursor by the identity's fixed length only after the provider accepts the operation. The helper bytes never occupy compiler workspace. The provider operation serializes as ordinary image records and adds no NOBJ record class or relocation phase.
For a flat artifact, the runtime base is imageBase plus the exact startup-stub length. For every banked image, the runtime base is bankWindowBase + 3. The entry bank's first instruction transfers over that runtime to startup. The ROM-mode copy-source operand is emitted as a placeholder. After the final code and read-only offsets are known, the compiler emits its resolved patch record. The startup transfer to main uses the same checked patch discipline.
4.3 Initial state
Before main begins, the runtime vectors have their adapter-selected targets, every program variable has its language-defined zero or explicit static value, and every aggregate constant has its complete declared value. In ROM mode startup unconditionally copies the complete initialized block, including the nonempty vector table and any initialized-variable bytes, then clears BSS. The copy therefore cannot be elided merely because source declares no initialized variable. In loaded mode startup omits the copy and clears BSS. Startup never copies aggregate-constant bytes or exposes a partly initialized object to source execution.
Static words use little-endian order. Record and array initializers follow the packed layout in Chapter 3. A bounded-string initializer writes its length and decoded bytes, zeros payload bytes L + 1 through N, and writes $00 at N + 1. Those bytes beyond L remain outside source-readable string content. The compiler may reuse its existing one-object initializer buffer while building either a variable or an aggregate constant; it does not require a second read-only-image-sized workspace buffer.
4.4 Program entry and exit
The flat entry address is imageBase; a banked artifact publishes (entryBank, bankWindowBase). Startup optionally establishes the stack, unconditionally copies the complete initialized block in ROM mode, clears BSS, and then enters main. Copy and clear therefore precede the entry transfer. In inherited-stack mode the transfer is a patched JP main; main returns through the caller's existing return address. In established-stack mode startup uses a patched CALL main, restores the incoming SP after successful completion, and then returns to the original caller. Failure and trap paths restore it through their terminal handling under Section 6.4.
In a banked artifact, the entry-bank instruction at bankWindowBase is an ordinary three-byte JP startup. It preserves the monitor-supplied stack while keeping every bank's runtime base and helper addresses identical.
Startup invokes main with no source parameters. Successful return terminates normally. Failure returned by main performs unhandled-error. No source routine runs before all variables and aggregate constants have their complete initial values.
The compiler emits no reset, restart, or interrupt vector table. A loader, monitor, or machine reset binding enters flat imageBase or the published banked entry pair outside the source language.