# V3 step 7.1 — self-hosted syslib: SysShim + FileIO (done 2026-09-22)

Follows the step-7 analysis. Rather than force one `FileIO` under
two ABIs (host gm2 NUL-terminated strings vs V3 length-prefixed
descriptors), this lands the **self-hosted syslib** the stage-2
compiler will link: `runtime/syslib/SysShim` + `runtime/syslib/FileIO`
— V3-only, descriptor-aware, over the existing C shim. Suite 103/103.

## `runtime/syslib/SysShim`

Descriptor-aware externals over `shim.c`: `fopenread`/`fopenwrite`
(→ ADDRESS), `fclose`, `fread` (bulk, sets the buffer's length),
`fputc`, `fputs`, `fwriteln`, `fwriteintw`, `stdout`/`stderr`
(→ ADDRESS), `arg` (argv via `/proc/self/cmdline`). Statement-like
operations are proper procedures (V3's 233 forbids
function-as-statement); value-returning ones are functions.

## `runtime/syslib/FileIO`

The compiler's FileIO subset, reimplemented over `SysShim` only:
`File` = `ADDRESS`; `Open`/`Close`/`ReadBytes`/`Write`/`WriteLn`/
`WriteString`/`WriteInt`/`WriteCard`/`NextParameter`, plus
`SLENGTH`/`Assign`/`Extract`/`Concat`/`Compare` and the classic
constants. This is the stage-2 counterpart of the host `FileIO`
used to bootstrap; the stage-1 gm2 build keeps the host library
(the standard bootstrap split, as Blaise does with FPC).

## Test

`FioProg` → 42: writes `"hello\n"` via the self-hosted FileIO, opens
it for read, `ReadBytes` (which sets the buffer's length), and checks
`buf[0] = 'h'` and length 6. Harness links `shim.c`.

## Stage-2 port items found (Redux / ABI)

Compiling the compiler's own sources with V3 will also need:
- Redux cleanups in those sources: `0C`/`15C`/`177C` octal char-code
  literals → `CHR(n)` (V3 has no `C` suffix), and `&`/`~`/`<>` →
  `AND`/`NOT`/`#`.
- A `DEFINITION MODULE FOR "C"` + `EXPORT UNQUALIFIED` V3 dialect
  only if a single FFI definition must also compile under gm2
  (not needed for the current split).

## Files

`runtime/syslib/SysShim.def|.mod`, `runtime/syslib/FileIO.def|.mod`,
`compiler/tests/fio_prog.mod`, `compiler/run_tests.sh`.
Step 7 remains "in progress": the compiler-source Redux sweep and
the `FileIO` selection between stages are the remaining tasks.