ww/test/wcc/765_star_fn_deref.c

/*
 * 765_star_fn_deref — root-cause lock for project #185. Pre-fix master
 * (5478695 baseline, post-#180), the cgen N_UN TK_STAR arm applied
 * the generic pointer-load `MOVQ (AX), AX` to a *fn operand. cgexpr
 * on the operand already left AX = fn-addr (post-#180 LEAQ); the
 * spurious second load then read the first instruction word and the
 * subsequent CALL AX jumped through that junk address, segfaulting.
 *
 * Fix: cmd/w6c/cgen.c N_UN TK_STAR opens with a TY_NAMED-peel +
 * TY_FN early-break — leave AX as the fn-addr cgexpr produced.
 * Selfhost twin in selfhost/cmd/wcc/cgenexpr.ww cgun TK_STAR uses the
 * same shape via tinfo.kind walk (TY_NAMED peel then TY_FN check),
 * mirroring ref/harec/src/check.c expr_call's
 * STORAGE_POINTER→STORAGE_FUNCTION path (harec skips the deref since
 * the pointer IS the address).
 *
 * #181 deferral: wwstage's checker bails asserttyped on the
 * `(*f)(...)` deref-call N_CALL shape (filed as project #181 — type_
 * stamp gap on the call-of-derefed-fn-ptr). Until #181 lands the
 * wwstage rows can't even reach cgen, so every row in this fixture
 * is gated CSTAGE-ONLY via stage_mask. Symmetry of the wwstage cgen
 * change is covered indirectly by the 990-997 self-build byte-id
 * gates (any cgen-side asymmetry would surface there); #181's own
 * probe will lock the wwstage runtime once the bail lifts.
 *
 * GATE-BLIND RISK (ken's note): byte-id alone cannot catch this
 * class — both stages drop the SAME instruction symmetrically, so
 * cs.s == ww.s holds either way. Runtime exit-code is the only
 * correctness net here, hence the multi-row table covering callee
 * shapes that exercise distinct ABI codepaths.
 *
 * Coverage:
 *   1. minimal              — `let f = &add1; (*f)(7) == 8`
 *   2. branched_callee      — pick aa or bb by runtime cond; verify
 *                             the SELECTED fn is actually invoked
 *                             (#105 lesson: single-callee masks via
 *                             address-constant aliasing)
 *   3. alias_chain          — `let f = &fn; let g = f; (*g)(7)` —
 *                             catches if cgen re-evaluates *f after
 *                             the assignment
 *   4. fn_with_args         — multiple args, scalar + ptr mix; ABI
 *                             register layout survives the deref-
 *                             call
 *   5. fn_tuple_return      — (i64, str) return shape; multi-reg
 *                             return ABI survives the deref-call
 *
 * Gates per row:
 *   a. cstage builds (exit 0); proves the checker stamps the
 *      deref-call N_CALL on the cstage side.
 *   b. cstage runs and exits with the row's expected_exit; pre-fix
 *      every row was 139 (SIGSEGV).
 *
 * GATE POLARITY: must stay GREEN. A red here means either the cgen
 * TK_STAR TY_FN early-break regressed, or stage symmetry drifted
 * far enough to surface here (unlikely while wwstage rows stay
 * gated off).
 */
#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;
}

/* stage_mask bits — every row is cstage-only until #181 lifts the
 * wwstage asserttyped bail on `(*f)(x)`. STAGE_WW defined for
 * structural parity with 764. */
#define STAGE_CS	1
#define STAGE_WW	2

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

static const struct row rows[] = {
	{ "minimal",
	  "fn add1(x: i32) i32 = { return x + 1; };\n"
	  "export fn main() i32 = {\n"
	  "    let f: *fn(x: i32) i32 = &add1;\n"
	  "    return (*f)(7);\n"
	  "};\n",
	  8,
	  STAGE_CS },
	/* Branched-callee: the if-arm forces a runtime choice between
	 * two distinct fn addresses, defeating any constant-aliasing
	 * mask of the deref miscompile (#105 lesson). */
	{ "branched_callee",
	  "fn aa(x: i32) i32 = { return x; };\n"
	  "fn bb(x: i32) i32 = { return x + 100; };\n"
	  "export fn main() i32 = {\n"
	  "    let pick: i32 = 1;\n"
	  "    let f: *fn(x: i32) i32 = &aa;\n"
	  "    if (pick != 0) { f = &bb; };\n"
	  "    return (*f)(7);\n"
	  "};\n",
	  107,
	  STAGE_CS },
	{ "alias_chain",
	  "fn add1(x: i32) i32 = { return x + 1; };\n"
	  "export fn main() i32 = {\n"
	  "    let f: *fn(x: i32) i32 = &add1;\n"
	  "    let g: *fn(x: i32) i32 = f;\n"
	  "    return (*g)(7);\n"
	  "};\n",
	  8,
	  STAGE_CS },
	{ "fn_with_args",
	  "fn many(a: i32, b: i32, p: *i32) i32 = { return a + b + *p; };\n"
	  "export fn main() i32 = {\n"
	  "    let z: i32 = 5;\n"
	  "    let f: *fn(a: i32, b: i32, p: *i32) i32 = &many;\n"
	  "    return (*f)(3, 7, &z);\n"
	  "};\n",
	  15,
	  STAGE_CS },
	/* Tuple-return: exercises the multi-register return ABI through
	 * the deref-call. Tagged size 16B+ would also hit the AX:DX:CX
	 * convention; (i64, str) keeps it simple while still covering
	 * the multi-reg path. */
	{ "fn_tuple_return",
	  "fn pair(x: i32) (i32, i32) = { return (x, x + 1); };\n"
	  "export fn main() i32 = {\n"
	  "    let f: *fn(x: i32) (i32, i32) = &pair;\n"
	  "    let a, b = (*f)(7);\n"
	  "    return a + b;\n"
	  "};\n",
	  15,
	  STAGE_CS },
};

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

static void
cleanup_tmp(const char *tmpdir)
{
	char p[512];
	snprintf(p, sizeof p, "rm -rf %s", tmpdir);
	runwait(p);
}

static int
build_via_driver(const char *driver, const char *outbin, const char *src)
{
	char cmd[1024];
	snprintf(cmd, sizeof cmd, "timeout 180 %s build -o %s %s 2>/dev/null",
	    driver, outbin, src);
	return runwait(cmd);
}

/* run_row — build + run; returns the binary's exit code (-1 on
 * build failure). expected_exit comparison done at the call site. */
static int
run_row(const char *driver, const struct row *r, int seq)
{
	char tmpdir[256], src[256], outbin[512];
	snprintf(tmpdir, sizeof tmpdir, "/tmp/wcsfd_%d_d_%d", getpid(), seq);
	snprintf(src,    sizeof src,    "%s/main765.ww", tmpdir);
	snprintf(outbin, sizeof outbin, "%s/main765", tmpdir);
	mkdir(tmpdir, 0755);
	if (write_source(src, r->src) != 0) {
		cleanup_tmp(tmpdir);
		return -1;
	}
	int rc = -1;
	if (build_via_driver(driver, outbin, src) == 0)
		rc = runwait(outbin);
	cleanup_tmp(tmpdir);
	return rc;
}

int
main(void)
{
	const char *bin = getenv("BIN");
	if (!bin) bin = "out/bin";
	char absbin[1024];
	if (bin[0] != '/') {
		char cwd[1024];
		if (getcwd(cwd, sizeof cwd) == NULL) return 1;
		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
		bin = absbin;
	}

	char cdrv[1024];
	snprintf(cdrv, sizeof cdrv, "%s/ww", bin);

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

	for (int i = 0; i < n; i++) {
		if (rows[i].stage_mask & STAGE_CS) {
			total++;
			int got = run_row(cdrv, &rows[i], seq++);
			if (got != rows[i].expected_exit) {
				fprintf(stderr,
				    "star_fn_deref[cstage][%s]: exit=%d want=%d\n",
				    rows[i].label, got, rows[i].expected_exit);
				fail++;
			}
		}
		/* STAGE_WW path intentionally absent — see header #181
		 * deferral note. When #181 lands and the wwstage runtime
		 * gate flips on, mirror the 764 wdrv runwait pattern. */
	}

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