ww build: honor Go output permission modes

cmd/w6l/main.c

@@ -8,8 +8,8 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <fcntl.h>
 #include <unistd.h>
-#include <sys/stat.h>
 
 /* `path` is acceptable iff it's either an archive ("!<arch>\n") or
  * an ELF file ("\x7fELF"). Distros often ship lib<name>.so as a GNU
@@ -121,17 +121,23 @@ main(int argc, char **argv)
 		return 1;
 	}
 
-	FILE *f = fopen(out, "wb");
+	/* BuildInstallFunc creates ordinary linked commands with 0777 and lets the
+	 * caller's umask select the installed mode.  Public ww builds link into a
+	 * fresh transaction stage, whose inode is later renamed to the output. */
+	int fd = open(out, O_WRONLY | O_CREAT | O_TRUNC, 0777);
+	if (fd < 0) {
+		fprintf(stderr, "w6l: cannot open %s\n", out);
+		return 1;
+	}
+	FILE *f = fdopen(fd, "wb");
 	if (f == NULL) {
+		close(fd);
+		(void)unlink(out);
 		fprintf(stderr, "w6l: 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(out, 0755) != 0) {
-		fprintf(stderr, "w6l: cannot make %s executable\n", out);
-		rc = 1;
-	}
 	free(inputs);
 	return rc;
 }