nx_dwarf_line.nx

nx_dwarf_line.nx -- DWARF v5 .debug_line section builder. Maps machine-instruction addresses back to source-file line + col. Enables `gdb` (and our future sovereign debugger) to show the .nx source line when stopped at any RV64 PC. DWARF v5 line program (DWARF 5 spec §6.2): .debug_line consists of one "line number program" per compilation unit. Header (~30 bytes), then a sequence of standard + extended opcodes that build a "line table" via a small VM: state: address (u64), op_index, file, line, column, is_stmt, basic_block, end_sequence, prologue_end, epilogue_begin, isa, discriminator Standard opcodes drive the VM: DW_LNS_copy commit current row DW_LNS_advance_pc += operand uleb128 DW_LNS_advance_line += signed leb DW_LNS_set_file := operand DW_LNS_set_column := operand ... etc Why now (R2 capability lever): * Managed platforms (V8/WASM) can't give us proper PC-to-source debugging at the silicon level. We can. * Pairs with nx_dbg.nx (future) for full sovereign debugging: read .debug_line, decode VM, print source location at faults. * F6-deterministic: same source -> same .debug_line bytes. What we ship here (v0.0.1): * Builder for the .debug_line bytes (header + line program). * uleb128 / sleb128 encoders (used widely in DWARF). * Helper to register (address, file, line) tuples and finalize. What we DEFER (separate commits):