ww: import toolchain — C bootstrap + ww-side self-host (phases 0-10)

C bootstrap (phases 0-9):
  cmd/wwc, cmd/6c, cmd/6a, cmd/6l, cmd/ww, rt, lib/*.

ww-side self-host (phase 10):
  selfhost/cmd/wwc — ww-cgen frontend; bootstrap fixed point.
  selfhost/cmd/6a  — assembler; byte-identical to C 6a (test 991).
  selfhost/cmd/6l  — linker w/ archive (.a) support; byte-identical
                     to C 6l (test 992).
  selfhost/cmd/ww  — driver (build/run/version); byte-identical to
                     C ww (test 993).

make test: 15/15. make bootstrap: ww2.s == ww3.s, ww2.o == ww3.o,
ww2 == ww3 byte-identical, with the full ww-tooled chain.

cmd/6l/main.c

@@ -0,0 +1,73 @@
+/*
+ * 6l — amd64 static linker. Reads relocatable ELF .o files, resolves,
+ * relocates, writes a static ELF executable.
+ *
+ *   6l -o out file1.o file2.o ...
+ *
+ * The first symbol named "_start" defined among the inputs becomes
+ * the entry point. If none is found, fall back to "main".
+ */
+#include "l.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int
+main(int argc, char **argv)
+{
+	const char *out = NULL;
+	const char **inputs = calloc(argc, sizeof *inputs);
+	int ninputs = 0;
+	u64 base = 0x400000;
+
+	for (int i = 1; i < argc; i++) {
+		if (strcmp(argv[i], "-o") == 0 && i + 1 < argc) {
+			out = argv[++i];
+		} else if (argv[i][0] == '-') {
+			fprintf(stderr, "6l: unknown flag %s\n", argv[i]);
+			return 2;
+		} else {
+			inputs[ninputs++] = argv[i];
+		}
+	}
+	if (out == NULL || ninputs == 0) {
+		fputs("usage: 6l -o exe file1.o [file2.o...]\n", stderr);
+		return 2;
+	}
+
+	Lnk l = {0};
+	/* Seed the symbol table with the entry point so archive pulls
+	 * include the .o that defines it. Without this, a libwwrt.a
+	 * containing start.o is silently skipped if no user .o
+	 * references _start, and the entry falls back to main — which
+	 * has no proper exit path. */
+	(void)l_intern(&l, "_start");
+	for (int i = 0; i < ninputs; i++) {
+		if (l_load(&l, inputs[i]) != 0) return 1;
+	}
+	if (l_resolve(&l) != 0) return 1;
+	if (l_relocate(&l, base + 0x1000) != 0) return 1;
+
+	Lsym *entry = l_lookup(&l, "_start");
+	if (entry == NULL || !entry->defined) entry = l_lookup(&l, "main");
+	if (entry == NULL || !entry->defined) {
+		fprintf(stderr, "6l: no _start or main symbol defined\n");
+		return 1;
+	}
+
+	FILE *f = fopen(out, "wb");
+	if (f == NULL) {
+		fprintf(stderr, "6l: cannot open %s\n", out);
+		return 1;
+	}
+	int rc = l_emit_elf(&l, f, base, base + 0x1000 + entry->val);
+	fclose(f);
+	if (rc == 0) {
+		/* chmod +x */
+		char cmd[1024];
+		snprintf(cmd, sizeof cmd, "chmod +x %s", out);
+		(void)system(cmd);
+	}
+	free(inputs);
+	return rc;
+}