Avoid linker errors on Windows with long command lines

NEWS.md

@@ -17,6 +17,8 @@
   coverage database file instead of a top-level unit name.
 - The `--force-init` command which was deprecated in the 1.7 release has
   been removed.
+- Elaboration of large designs on Windows no longer fail with linker
+  errors due to excessive command line length.
 
 ## Version 1.13.1 - 2024-07-25
 - Windows installer was missing some standard library files.

src/cgen.c

@@ -62,6 +62,7 @@ static A(char *) link_args;
 static A(char *) cleanup_files = AINIT;
 
 #define UNITS_PER_JOB 25
+#define LARGE_OBJECT_COUNT 10
 
 static void cgen_find_children(vcode_unit_t root, unit_list_t *units)
 {
@@ -215,8 +216,29 @@ static void cgen_link(const char *module_name, char **objs, int nobjs)
    cgen_link_arg("-o");
    cgen_link_arg("%s", so_path);
 
-   for (int i = 0; i < nobjs; i++)
-      cgen_link_arg("%s", objs[i]);
+   char *tmplist = NULL;
+   if (nobjs >= LARGE_OBJECT_COUNT) {
+      // If there are a large number of objects to link then pass them
+      // in a file rather than individually to avoid command line length
+      // limits on Windows
+
+      tmplist = nvc_temp_file();
+
+      FILE *f = fopen(tmplist, "w");
+      if (f == NULL)
+         fatal_errno("%s", tmplist);
+
+      for (int i = 0; i < nobjs; i++)
+         fprintf(f, "%s\n", objs[i]);
+
+      fclose(f);
+
+      cgen_link_arg("@%s", tmplist);
+   }
+   else {
+      for (int i = 0; i < nobjs; i++)
+         cgen_link_arg("%s", objs[i]);
+   }
 
 #if defined LINKER_PATH && defined __OpenBSD__
    // Extra linker arguments to make constructors work on OpenBSD
@@ -250,6 +272,13 @@ static void cgen_link(const char *module_name, char **objs, int nobjs)
          fatal_errno("unlink: %s", objs[i]);
    }
 
+   if (tmplist != NULL) {
+      if (unlink(tmplist) != 0)
+         fatal_errno("unlink: %s", tmplist);
+
+      free(tmplist);
+   }
+
    progress("linking shared library");
 
    for (size_t i = 0; i < link_args.count; i++)