Struct EndpointDescriptor 

#[repr(C)]
pub struct EndpointDescriptor {
    pub fn_ptr: fn(u64) -> u64,
    pub index: u8,
    pub arg_registers: u8,
    pub arg_cnode_size: u8,
    pub _pad: [u8; 5],
}

Descriptor written into the .subsoil.endpoints ELF section by the endpoint attribute macro. The JAVM transpiler reads this section at link time and uses each entry to populate the chain Image’s endpoints: BTreeMap<u8, EndpointDef> field.

Layout is #[repr(C)] so the transpiler can decode the section as a flat array of fixed-size records. On RISC-V64 the function pointer occupies 8 bytes, followed by 8 bytes of metadata, for a total stride of 16 bytes.

Fields

fn_ptr: fn(u64) -> u64

RISC-V address of the endpoint function. The transpiler maps this to a PVM PC via its instruction-mapping table.

index: u8

Endpoint index (key in the chain Image’s endpoints map).

arg_registers: u8

Caller-supplied register-arg count (per Image::EndpointDef).

arg_cnode_size: u8

Caller-supplied arg-cnode size (per Image::EndpointDef).

_pad: [u8; 5]

Reserved for alignment / future expansion.