Module layout 

Shared program data-region layout for transpiler-emitted Images.

ProgramLayout assigns cap_index, base_page, and page_count to each DATA cap appearing in a transpiler-emitted Image. The consumer is crate::linker::link_elf, which uses ProgramLayout::stack_top to compute the initial SP value baked into every endpoint’s [javm_cap::image::EndpointDef::initial_regs]. The page-count and base-page metadata also feed declarative Image.memory_mappings.

Cap-index convention: 65 = stack, 66 = ro, 67 = rw, 68 = heap. Code is not a cap — it is the Image’s dedicated code field mapped read-only at CODE_BASE. Data is laid out from javm_cap::layout::DATA_BASE (256 MiB) upward and stacks linearly: stack lives at [DATA_BASE, DATA_BASE + stack_pages), ro at [DATA_BASE + stack_pages, …), etc.

Structs

DataCapEntry

One DATA cap’s layout: where it lives in the manifest and where it maps in guest memory.

ProgramLayout

Full DATA-cap layout of a transpiler-emitted blob. stack is always present; ro, rw, heap are present only when their page count is non-zero. Args bytes are delivered separately (kernel-allocated cap at bare-Frame slot 4), so they are not part of the layout.

Constants

CODE_BASE

Guest virtual address where the code region is mapped read-only.

DATA_BASE

Re-exported PVM2 ABI layout constants (see [javm_cap::layout]). Guest virtual address where the data region begins. All data caps (stack / ro / rw / heap) and instance overlays live in [DATA_BASE, 4 GiB). At 256 MiB, well clear of the largest permitted code region.

HEAP_CAP_INDEX

Cap index of the heap DATA cap.

MAX_CODE_SIZE

Re-exported PVM2 ABI layout constants (see [javm_cap::layout]). Maximum byte length of the code region. Code occupies [CODE_BASE, CODE_BASE + code_len) and must stay below DATA_BASE, so code_len ≤ DATA_BASE − CODE_BASE = 252 MiB.

PVM_PAGE_SIZE

PVM page size in bytes.

RO_CAP_INDEX

Cap index of the read-only DATA cap (.rodata).

RW_CAP_INDEX

Cap index of the read-write DATA cap (.data + .bss).

STACK_CAP_INDEX

Cap index of the stack DATA cap.