w6a/ww: DATAR naming an undefined slot is a loud reject

A DATAR relocation against an undefined data slot was silently
dropped — the relocation vanished from the object. Reject loudly,
matching the cstage single-pass resolution behavior.

Makefile

@@ -264,6 +264,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_loopcap_run \
 	  $(BIN)/test_enumcap_run \
 	  $(BIN)/test_wwdumpgate_run \
+	  $(BIN)/test_datargate_run \
 	  $(BIN)/test_ampfncollide_run \
 	  $(BIN)/test_trycallcollide_run \
 	  $(BIN)/test_gunsigned_run \
@@ -837,6 +838,14 @@ $(BIN)/test_wwdumpgate_run: test/wcc/989_wwdumpgate_run.c \
 		$(BIN)/wwdump $(BIN)/wwdump_ww | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+# 989_datargate_run (#59, F15 c5): w6a loud-rejects a DATAR relocation whose
+# slot was never defined by a prior DATAW instead of silently dropping the
+# reloc (zero-filled pointer slot in the .o). Runs w6a + w6a_ww directly and
+# asserts a byte-identical .o on the healthy path (rule-10). See the header.
+$(BIN)/test_datargate_run: test/wcc/989_datargate_run.c \
+		$(BIN)/w6a $(BIN)/w6a_ww | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 # 989_ampfncollide_run (#4, c2): `&fn` synthesis (unoptype TK_AMP +
 # assignableaddrfn) prefers the current module's fn when a same-leaf fn is
 # declared in a later module. Builds/rejects on BOTH driver twins (rule-10).

selfhost/cmd/w6a/asm.ww

@@ -300,10 +300,17 @@ export fn encode(a: *asm_) i32 = {
 			// pointing at target. Slot must already be defined
 			// by a prior DATAW.
 			let holder: *asym = intern(a, p.from.asym);
-			if (holder.defined == 0) {
-				p = p.link; continue;
-			};
-			if (holder.isdata == 0) {
+			// #59: a DATAR slot with no prior DATAW definition must be
+			// a loud error, not a silently dropped relocation (the .o
+			// would ship a zero-filled pointer slot — a null pointer at
+			// link/runtime). Mirrors cmd/w6a/asm.c:363 (errs++ → main
+			// returns 1 before opening the output, so no .o is written).
+			if (holder.defined == 0 || holder.isdata == 0) {
+				let msg: str = "w6a: DATAR slot not yet defined as DATAW: ";
+				os.write(2, msg.ptr, msg.len: u64);
+				os.write(2, p.from.asym.ptr, p.from.asym.len: u64);
+				os.write(2, "\n".ptr, 1u64);
+				a.errs += 1;
 				p = p.link; continue;
 			};
 			let target: *asym = intern(a, p.to.asym);

selfhost/cmd/w6a/main.combined.ww

@@ -4023,10 +4023,17 @@ export fn encode(a: *asm_) i32 = {
 			// pointing at target. Slot must already be defined
 			// by a prior DATAW.
 			let holder: *asym = intern(a, p.from.asym);
-			if (holder.defined == 0) {
-				p = p.link; continue;
-			};
-			if (holder.isdata == 0) {
+			// #59: a DATAR slot with no prior DATAW definition must be
+			// a loud error, not a silently dropped relocation (the .o
+			// would ship a zero-filled pointer slot — a null pointer at
+			// link/runtime). Mirrors cmd/w6a/asm.c:363 (errs++ → main
+			// returns 1 before opening the output, so no .o is written).
+			if (holder.defined == 0 || holder.isdata == 0) {
+				let msg: str = "w6a: DATAR slot not yet defined as DATAW: ";
+				os.write(2, msg.ptr, msg.len: u64);
+				os.write(2, p.from.asym.ptr, p.from.asym.len: u64);
+				os.write(2, "\n".ptr, 1u64);
+				a.errs += 1;
 				p = p.link; continue;
 			};
 			let target: *asym = intern(a, p.to.asym);

test/wcc/989_datargate_run.c

@@ -0,0 +1,139 @@
+/*
+ * 989_datargate_run (#59, F15 c5) — w6a must loud-reject a DATAR relocation
+ * whose slot was never defined by a prior DATAW, not silently drop the reloc.
+ *
+ * THE BUG (wwstage w6a only, cat-A silent wrong output under rc=0): asm.ww's
+ * A_DATAR arm, when holder.defined==0 or holder.isdata==0, did `p = p.link;
+ * continue;` with no diagnostic and no errs++ — so the R_X86_64_64 .data
+ * relocation was silently dropped and a rc=0 .o was emitted with a zero-filled
+ * pointer slot (a null pointer at link/runtime). The cstage twin (cmd/w6a/
+ * asm.c:363) printed a diagnostic + a->errs++, and main returns 1 before
+ * opening the output, so no .o is written. THE FIX: emit a diagnostic and bump
+ * a.errs (encode returns a.errs → main returns 1 before writing the .o).
+ *
+ *   row | shape                         | result (cs & ww agree)
+ *   ----+-------------------------------+--------------------------------
+ *   bad | DATAR on a slot with no DATAW | rc != 0, no .o written
+ *   ok  | DATAW then DATAR on that slot | rc == 0, .o byte-identical (cs==ww)
+ *
+ * bad was RED pre-c5 on wwstage (rc=0, .o with the reloc silently dropped).
+ * ok pins the defined-slot path: both stages rc=0 and a byte-identical .o.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.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;
+}
+
+static const char *BAD =
+	"TEXT f,$0\n\tRET\n\tDATAR x+0(SB), f(SB)\n";
+static const char *OK =
+	"TEXT f,$0\n\tRET\n"
+	"DATAW x(SB),\"\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x00\"\n"
+	"\tDATAR x+0(SB), f(SB)\n";
+
+static int
+write_file(const char *path, const char *body)
+{
+	FILE *f = fopen(path, "wb");
+	if (!f) return -1;
+	fputs(body, f);
+	fclose(f);
+	return 0;
+}
+
+/* Assemble `src` with `tool` into `obj` (removed first). Returns rc; sets
+ * *exists to whether the .o was created. */
+static int
+assemble(const char *tool, const char *src, const char *obj, int *exists)
+{
+	char cmd[1024];
+	unlink(obj);
+	snprintf(cmd, sizeof cmd, "%s -o %s %s 2>/dev/null", tool, obj, src);
+	int rc = runwait(cmd);
+	if (exists) *exists = (access(obj, F_OK) == 0);
+	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 ctool[1024], wtool[1024];
+	snprintf(ctool, sizeof ctool, "%s/w6a", bin);
+	snprintf(wtool, sizeof wtool, "%s/w6a_ww", bin);
+	int have_ww = (access(wtool, X_OK) == 0);
+	if (!have_ww)
+		fprintf(stderr, "datargate: skip wwstage (no %s)\n", wtool);
+
+	char bads[64], oks[64], co[64], wo[64];
+	snprintf(bads, sizeof bads, "/tmp/datarg_bad_%d.s", getpid());
+	snprintf(oks, sizeof oks, "/tmp/datarg_ok_%d.s", getpid());
+	snprintf(co, sizeof co, "/tmp/datarg_c_%d.o", getpid());
+	snprintf(wo, sizeof wo, "/tmp/datarg_w_%d.o", getpid());
+	if (write_file(bads, BAD) || write_file(oks, OK)) return 1;
+
+	int fail = 0, total = 0, ex;
+
+	/* bad: both stages loud, no .o */
+	total++;
+	if (assemble(ctool, bads, co, &ex) == 0 || ex) {
+		fprintf(stderr, "datargate[cstage][bad]: rc=0/.o written on "
+		    "undefined DATAR slot\n");
+		fail++;
+	}
+	if (have_ww) {
+		if (assemble(wtool, bads, wo, &ex) == 0 || ex) {
+			fprintf(stderr, "datargate[wwstage][bad]: rc=0/.o written on "
+			    "undefined DATAR slot — reloc silently dropped (#59)\n");
+			fail++;
+		}
+	}
+
+	/* ok: both stages rc=0, byte-identical .o */
+	total++;
+	int crc = assemble(ctool, oks, co, &ex);
+	if (crc != 0 || !ex) {
+		fprintf(stderr, "datargate[cstage][ok]: rc=%d .o=%d\n", crc, ex);
+		fail++;
+	}
+	if (have_ww) {
+		int wrc = assemble(wtool, oks, wo, &ex);
+		if (wrc != 0 || !ex) {
+			fprintf(stderr, "datargate[wwstage][ok]: rc=%d .o=%d\n", wrc, ex);
+			fail++;
+		}
+		char cmp[1024];
+		snprintf(cmp, sizeof cmp, "cmp -s %s %s", co, wo);
+		if (runwait(cmp) != 0) {
+			fprintf(stderr, "datargate[ok]: cs/ww .o differ (#59)\n");
+			fail++;
+		}
+	}
+
+	unlink(bads); unlink(oks); unlink(co); unlink(wo);
+
+	if (fail) {
+		fprintf(stderr, "datargate_run: %d check(s) failed\n", fail);
+		return 1;
+	}
+	printf("datargate_run: %d/%d ok\n", total, total);
+	return 0;
+}