evv/gw-basic-2026

Files

Eremey Valetov 20ecdae938 Add --warn and --safe memory safety flags to the compiler

Three progressive levels for gwbasic-compile:

--warn: static analysis warnings (uninitialized variables, GOTO to
nonexistent line, unreachable code detection). Zero runtime cost.

--safe (implies --warn): runtime checked integer arithmetic via
gw_int_add/sub/mul/neg matching real GW-BASIC overflow semantics,
enhanced array bounds diagnostics with variable names and line numbers,
GOSUB stack overflow diagnostics with source line reporting.

--safe=sanitize (implies --safe): passes -fsanitize=address,undefined
to gcc for full memory error detection.

Also: fix pre-existing missing closing paren in array LET-to-integer
codegen, add strpool_pin/unpin infrastructure, add compiler optimization
flags and memory safety sections to roadmap.

72/72 interpreter tests pass. 64/64 eligible compiler tests pass in
--safe mode.

2026-04-09 13:14:26 -04:00

4.7 KiB

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Roadmap

Completed

Ahead-of-Time Compiler (v0.16.0)

gwbasic-compile translates tokenized .bas programs to C source, then invokes GCC to produce native executables linked against libgwrt.a.

Pipeline: .bas → gw_crunch() → analysis pass → C codegen → gcc → native binary.

69 of 69 eligible tests pass (100%). Zero compile errors.

Language coverage:

All statements: PRINT, LET, IF/THEN/ELSE, GOTO, GOSUB/RETURN, FOR/NEXT, WHILE/WEND, ON GOTO/GOSUB, ON ERROR GOTO, RESUME/RESUME NEXT, DIM, DEF FN, SWAP, READ/DATA/RESTORE, INPUT/LINE INPUT, OPEN/CLOSE/PRINT#/INPUT#/WRITE#, FIELD/LSET/RSET/GET/PUT, BSAVE/BLOAD, SAVE/LOAD, CHAIN/COMMON, SCREEN, PSET/PRESET, COLOR/LOCATE/CLS, CIRCLE/DRAW/PAINT/PLAY, VIEW/WINDOW/PALETTE, POKE/OUT/WAIT, DEF SEG, RANDOMIZE, CLEAR, MID$ assignment, ERROR, KILL/NAME/FILES/SHELL/MKDIR/CHDIR/RMDIR, ENVIRON, LPRINT/LLIST, WIDTH, KEY
All operators: + - * / \ MOD ^ AND OR XOR NOT EQV IMP > < = <= >= <> (including string comparison via strcmp)
All functions: math, string, file, conversion (CVI/CVS/CVD/MKI$/MKS$/MKD$), graphics (POINT/PMAP), system (FRE/ERR/ERL/TIMER/DATE$/TIME$/ENVIRON$/INKEY$)
Token embedding for complex statements (PRINT USING, DEF FN, graphics, file I/O, MID$ assignment) with selective variable sync
Division-by-zero detection, RNG matching (gw_rnd), ON ERROR GOTO via setjmp/longjmp

Optimizations:

Constant folding (compile-time arithmetic on literals)
Dead code elimination (skip statements after GOTO/END/STOP)
FOR step=1 elision (var++ instead of step variable, simple comparison)
Fast-path expression emitter (skip buffering for common case)
Selective variable sync in delegated statements
REM-line skip (no runtime check for comment-only lines)

Hardware I/O Simulator (v0.15.0)

Implemented in portio.c / portio.h following the virmem.c dispatch pattern. Emulates 8253 PIT channel 2 (speaker frequency), PPI port B (speaker on/off with continuous tone via PulseAudio), CGA mode/color registers, game port (joystick stub), and COM1 serial (transmitter-ready stub). Default: reads return 0xFF (floating bus), writes discarded.

Also in v0.15.0: 100% token coverage (all 144 GW-BASIC tokens handled), string space pool with compacting garbage collector, RESET, ENVIRON/ENVIRON$, ERDEV/ERDEV$, IOCTL/IOCTL$, LCOPY, DATE$/TIME$ assignment, CALL, COM.

Jupyter Kernel (v0.15.0)

gwbasickernel/ -- Jupyter notebook kernel using the persistent subprocess model with sentinel protocol.

Inline Sixel graphics -- pure-Python Sixel decoder renders SCREEN commands as inline PNG images in the notebook
INPUT statement support via Jupyter stdin protocol
Pygments syntax highlighting for code cells
Tab completion for all GW-BASIC keywords
Magic commands: %reset, %timeout, %new

Install: pip install -e . && gwbasickernel-install --user

Next Up

Compiler Memory Safety (`--warn` / `--safe`)

--warn -- static analysis warnings (uninitialized variables, GOTO to nonexistent line, unreachable code, FOR/GOSUB nesting depth)
--safe -- runtime safety checks in generated C: checked integer arithmetic via gw_int_add/sub/mul (fixes int16_t overflow UB), enhanced array bounds diagnostics with line numbers and variable names, GOSUB stack overflow diagnostics, string pool GC pinning
--safe=sanitize -- above plus -fsanitize=address,undefined passed to gcc

Compiler Optimization Flags

--no-gc-check -- skip gwrt_check_line() per-line calls (no string pool GC, no Ctrl+Break check) for maximum throughput
--inline-arrays -- emit direct array indexing for statically-DIMmed arrays instead of runtime gwrt_array_elem() lookup
--fast-math -- skip division-by-zero checks, allow unsafe float ops
-O0 through -O3 -- compiler-level optimization tiers mapping to different sets of codegen optimizations (constant folding, dead code elimination, FOR step=1 elision, fast-path expressions)

IDE Integration

VS Code extension -- syntax highlighting (TextMate grammar), snippets, run/debug tasks, integrated terminal runner
JetBrains plugin (IntelliJ/CLion) -- syntax highlighting, code completion, run configurations, debugger integration (breakpoints via STOP, variable inspection), structure view (line number outline)

Known Limitations

Maximum 256 variables, 64 arrays, 16 FOR nesting, 24 GOSUB nesting, 16 WHILE nesting
CALL/CALLS (machine code execution) raises Illegal function call
DATE$/TIME$ assignment accepted but does not modify the system clock
Device stubs (ERDEV, IOCTL, COM, LCOPY) return defaults

4.7 KiB Raw Blame History