# MARKUS MAIWALD (ARCHITECT) | VOXIS FORGE (AI)
# Rumpk Phase 8: The Summoning (ELF Loader)

import fs/tar, loader/elf

proc kprintln(s: cstring) {.importc, cdecl.}

# Assembly trampoline to jump to userland
proc rumpk_enter_userland(entry: uint64) {.importc, cdecl.}

proc kexec*(path: string) =
  kprintln(cstring("[Loader] Summoning: " & path))

  # 1. Read ELF File from VFS
  let file_content = vfs_read_file(path)
  if file_content.len == 0:
    kprintln("[Loader] Error: File not found or empty.")
    return

  # 2. Verify ELF Header
  let ehdr = cast[ptr Elf64_Ehdr](unsafeAddr file_content[0])

  if ehdr.e_ident[0] != 0x7F or ehdr.e_ident[1] != 'E'.uint8 or
     ehdr.e_ident[2] != 'L'.uint8 or ehdr.e_ident[3] != 'F'.uint8:
    kprintln("[Loader] Error: Invalid ELF magic.")
    return

  if ehdr.e_machine != 243: # EM_RISCV
    kprintln("[Loader] Error: Binary is not for RISC-V.")
    return

  # 3. Parse Program Headers
  let base_ptr = cast[uint64](unsafeAddr file_content[0])

  for i in 0 ..< int(ehdr.e_phnum):
    let phdr_offset = ehdr.e_phoff + uint64(i * int(ehdr.e_phentsize))
    let phdr = cast[ptr Elf64_Phdr](base_ptr + phdr_offset)

    if phdr.p_type == PT_LOAD:
      # Map Segment
      # kprintln("  Mapping Segment to 0x" & $phdr.p_vaddr & " size=" & $phdr.p_memsz)

      let dest = cast[ptr UncheckedArray[byte]](phdr.p_vaddr)
      let src = cast[ptr UncheckedArray[byte]](base_ptr + phdr.p_offset)

      # [DANGER] Single Address Space: We are trusting the binary doesn't overwrite the kernel!

      # Clear BSS (memsz > filesz)
      if phdr.p_memsz > 0:
        zeroMem(dest, phdr.p_memsz)

      # Copy Data
      if phdr.p_filesz > 0:
        copyMem(dest, src, phdr.p_filesz)

  # 4. Transfer Consciousness
  kprintln("[Loader] Transferring Consciousness...")
  rumpk_enter_userland(ehdr.e_entry)