ww/test/wcc/790_single_field_struct_zeroinit.c

/*
 * 790_single_field_struct_zeroinit — project #213 (≤8B-composite slice).
 * Pins that a bare `let b: T;` of an 8B single-field STRUCT zero-inits
 * the slot on BOTH stages byte-identically (rule-10), and that the
 * zero is observable (read-before-init sees 0, not stack garbage).
 *
 * THE BUG (wwstage cgen): wwstage's cglet no-rhs zero-init
 * (selfhost/cmd/wcc/cgenstmt.ww) only zeroed an 8B *primitive*
 * (scalar/ptr/fn/chan → MOVQ $0) or a `zsz > 8` composite (XORQ run).
 * An 8B *composite* (single-field struct/tagged) was NEITHER → it fell
 * through with no zero-init, while cstage emits `MOVQ $0` (cgen.c N_LET
 * `else if (sz == 8)`, per ww's bare-`let`-composite contract). So a
 * read-before-init saw stack garbage on wwstage but 0 on cstage —
 * cs!=ww byte-id (surfaced by #5's bufio `box { src: io.stream }`) AND
 * a latent silent miscompile. cstage is correct; align wwstage UP.
 *
 * SCOPE: 8B composites only. Sub-8 (4B/1B) composites are intentionally
 * left un-zeroed — cstage doesn't zero them either, so zeroing them on
 * wwstage would RE-diverge; that sub-8 read-before-init garbage is a
 * SHARED (cs==ww) latent, out of this slice.
 *
 *   row                | shape                                   | exit | byte-id
 *   -------------------+-----------------------------------------+------+--------
 *   field8_assign      | box{src:*vtable}; let b; b.src=&vt;      |  42  | cs==ww
 *                      |   read b.src.x — the 778/#5 shape        |      |
 *                      |   (#5-independent: no io/union)          |      |
 *   read_before_init   | box{x:i64}; dirty the stack, then bare   |   0  | cs==ww
 *                      |   `let b; return b.x` UNassigned — must  |      |
 *                      |   read 0 (the load-bearing zero-init,    |      |
 *                      |   was stack garbage pre-fix on wwstage)  |      |
 *
 * GATE POLARITY: must stay GREEN. Red on field8_assign = the 8B-struct
 * zero-init regressed (cs!=ww); red on read_before_init = the zero-init
 * stopped being emitted (garbage read).
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/wait.h>

static int
runwait(const char *cmd)
{
	int rc = system(cmd);
	if (rc == -1) return -1;
	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
	return -1;
}

#define STAGE_CS	1
#define STAGE_WW	2

struct row {
	const char *label;
	const char *src;
	int want_exit;
	int stage_mask;
	int byte_id;
};

static const struct row rows[] = {
	/* The 778/#5 shape, #5-independent: single-field struct bare-let
	 * then field-assign. Pre-fix cstage zero-inits b (dead here since
	 * b.src is assigned), wwstage omits it → cs!=ww. */
	{ "field8_assign",
	  "package main;\n"
	  "type vtable = struct { x: i32 };\n"
	  "type box = struct { src: *vtable };\n"
	  "fn use(b: *box) i32 = { return b.src.x; };\n"
	  "export fn main() i32 = {\n"
	  "	let vt: vtable; vt.x = 42;\n"
	  "	let b: box; b.src = &vt;\n"
	  "	return use(&b);\n"
	  "};\n",
	  42, STAGE_CS | STAGE_WW, 1 },

	/* The correctness lock: dirty the stack, then read an UNassigned
	 * 8B-struct field — must be 0 (zero-init), not garbage. */
	{ "read_before_init",
	  "package main;\n"
	  "type box = struct { x: i64 };\n"
	  "fn dirty() i64 = { let a: i64 = 0x7777777777777777i64; let b: i64 = a; return b; };\n"
	  "fn readit() i64 = { let b: box; return b.x; };\n"
	  "export fn main() i32 = {\n"
	  "	let j: i64 = dirty();\n"
	  "	let v: i64 = readit();\n"
	  "	if (v == 0i64) { return 0; };\n"
	  "	return 1;\n"
	  "};\n",
	  0, STAGE_CS | STAGE_WW, 1 },
};

static void
cleanup_tmp(const char *tmpdir, const char *base)
{
	char p[1024];
	snprintf(p, sizeof p, "%s/%s",             tmpdir, base); unlink(p);
	snprintf(p, sizeof p, "%s/%s.ww",          tmpdir, base); unlink(p);
	snprintf(p, sizeof p, "%s/%s.s",           tmpdir, base); unlink(p);
	snprintf(p, sizeof p, "%s/%s.o",           tmpdir, base); unlink(p);
	snprintf(p, sizeof p, "%s/%s.combined.ww", tmpdir, base); unlink(p);
	rmdir(tmpdir);
}

static int
write_source(const char *path, const char *src)
{
	FILE *f = fopen(path, "wb");
	if (!f) return -1;
	fputs(src, f);
	fclose(f);
	return 0;
}

static int
build_via_driver(const char *driver, const char *tmpdir, const char *src)
{
	char cmd[2048];
	snprintf(cmd, sizeof cmd, "cd %s && timeout 180 %s build %s 2>/dev/null",
	    tmpdir, driver, src);
	return runwait(cmd);
}

static int
run_row(const char *driver, const struct row *r, int seq)
{
	char tmpdir[256], src[512], base[64], outbin[768];
	snprintf(tmpdir, sizeof tmpdir, "/tmp/sfsz_%d_d_%d", getpid(), seq);
	snprintf(base,   sizeof base,   "main790");
	snprintf(src,    sizeof src,    "%s/%s.ww", tmpdir, base);
	mkdir(tmpdir, 0755);
	if (write_source(src, r->src) != 0) { cleanup_tmp(tmpdir, base); return -1; }
	int rc;
	if (build_via_driver(driver, tmpdir, src) == 0) {
		snprintf(outbin, sizeof outbin, "%s/%s", tmpdir, base);
		rc = runwait(outbin);
	} else {
		rc = -1;
	}
	cleanup_tmp(tmpdir, base);
	return rc;
}

static int
asm_byte_identical(const char *cdrv, const char *wdrv, const struct row *r,
    int seq)
{
	char src[512], tdc[256], tdw[256], base[64], cs[512], ws[512];
	snprintf(tdc, sizeof tdc, "/tmp/sfsz_%d_c_%d", getpid(), seq);
	snprintf(tdw, sizeof tdw, "/tmp/sfsz_%d_w_%d", getpid(), seq);
	snprintf(base, sizeof base, "main790");
	mkdir(tdc, 0755);
	mkdir(tdw, 0755);
	snprintf(src, sizeof src, "%s/%s.ww", tdc, base);
	if (write_source(src, r->src) != 0) { cleanup_tmp(tdc, base); cleanup_tmp(tdw, base); return -1; }
	int rc = -1;
	if (build_via_driver(cdrv, tdc, src) != 0) goto out;
	snprintf(cs, sizeof cs, "%s/%s.s", tdc, base);
	snprintf(src, sizeof src, "%s/%s.ww", tdw, base);
	if (write_source(src, r->src) != 0) goto out;
	if (build_via_driver(wdrv, tdw, src) != 0) goto out;
	snprintf(ws, sizeof ws, "%s/%s.s", tdw, base);
	FILE *fc = fopen(cs, "rb");
	FILE *fw = fopen(ws, "rb");
	if (fc && fw) {
		rc = 0;
		for (;;) {
			int a = fgetc(fc);
			int b = fgetc(fw);
			if (a != b) { rc = -1; break; }
			if (a == EOF) break;
		}
	}
	if (fc) fclose(fc);
	if (fw) fclose(fw);
out:
	cleanup_tmp(tdc, base);
	cleanup_tmp(tdw, base);
	return rc;
}

int
main(void)
{
	const char *bin = getenv("BIN");
	if (!bin) bin = "out/bin";
	char cwd[256];
	if (getcwd(cwd, sizeof cwd) == NULL) return 1;
	char absbin[512];
	if (bin[0] != '/') {
		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
		bin = absbin;
	}

	char cdrv[640], wdrv[640];
	snprintf(cdrv, sizeof cdrv, "%s/ww",    bin);
	snprintf(wdrv, sizeof wdrv, "%s/ww_ww", bin);

	int n = (int)(sizeof rows / sizeof rows[0]);
	int total = 0, fail = 0, seq = 0;
	int wwpresent = (access(wdrv, X_OK) == 0);

	for (int i = 0; i < n; i++) {
		const struct row *r = &rows[i];

		if (r->stage_mask & STAGE_CS) {
			total++;
			int got = run_row(cdrv, r, seq++);
			if (got != r->want_exit) {
				fprintf(stderr, "sfsz[cs][%s]: exit=%d want=%d\n",
				    r->label, got, r->want_exit);
				fail++;
			}
		}

		if (wwpresent && (r->stage_mask & STAGE_WW)) {
			total++;
			int got = run_row(wdrv, r, seq++);
			if (got != r->want_exit) {
				fprintf(stderr, "sfsz[ww][%s]: exit=%d want=%d\n",
				    r->label, got, r->want_exit);
				fail++;
			}
			if (r->byte_id) {
				total++;
				if (asm_byte_identical(cdrv, wdrv, r, seq++) != 0) {
					fprintf(stderr, "sfsz[byte-id][%s]: cstage vs wwstage asm differs\n",
					    r->label);
					fail++;
				}
			}
		}
	}

	if (fail) {
		fprintf(stderr, "single_field_struct_zeroinit: %d/%d checks failed\n",
		    fail, total);
		return 1;
	}
	printf("single_field_struct_zeroinit: %d/%d ok\n", total, total);
	return 0;
}