@@ -0,0 +1,200 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A simple modules_builtin reader.
+ *
+ * (C) 2014, 2022 Oracle, Inc.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "modules_builtin.h"
+
+/*
+ * Read a modules.builtin.objs file and translate it into a stream of
+ * name / module-name pairs.
+ */
+
+/*
+ * Construct a modules.builtin.objs iterator.
+ */
+struct modules_builtin_iter *
+modules_builtin_iter_new(const char *modules_builtin_file)
+{
+	struct modules_builtin_iter *i;
+
+	i = calloc(1, sizeof(struct modules_builtin_iter));
+	if (i == NULL)
+		return NULL;
+
+	i->f = fopen(modules_builtin_file, "r");
+
+	if (i->f == NULL) {
+		fprintf(stderr, "Cannot open builtin module file %s: %s\n",
+			modules_builtin_file, strerror(errno));
+		return NULL;
+	}
+
+	return i;
+}
+
+/*
+ * Iterate, returning a new null-terminated array of object file names, and a
+ * new dynamically-allocated module name.  (The module name passed in is freed.)
+ *
+ * The array of object file names should be freed by the caller: the strings it
+ * points to are owned by the iterator, and should not be freed.
+ */
+
+char ** __attribute__((__nonnull__))
+modules_builtin_iter_next(struct modules_builtin_iter *i, char **module_name)
+{
+	size_t npaths = 1;
+	char **module_paths;
+	char *last_slash;
+	char *last_dot;
+	char *trailing_linefeed;
+	char *object_name = i->line;
+	char *dash;
+	int composite = 0;
+
+	/*
+	 * Read in all module entries, computing the suffixless, pathless name
+	 * of the module and building the next arrayful of object file names for
+	 * return.
+	 *
+	 * Modules can consist of multiple files: in this case, the portion
+	 * before the colon is the path to the module (as before): the portion
+	 * after the colon is a space-separated list of files that should be
+	 * considered part of this module.  In this case, the portion before the
+	 * name is an "object file" that does not actually exist: it is merged
+	 * into built-in.a without ever being written out.
+	 *
+	 * All module names have - translated to _, to match what is done to the
+	 * names of the same things when built as modules.
+	 */
+
+	/*
+	 * Reinvocation of exhausted iterator. Return NULL, once.
+	 */
+retry:
+	if (getline(&i->line, &i->line_size, i->f) < 0) {
+		if (ferror(i->f)) {
+			fprintf(stderr, "Error reading from modules_builtin file:"
+				" %s\n", strerror(errno));
+			exit(1);
+		}
+		rewind(i->f);
+		return NULL;
+	}
+
+	if (i->line[0] == '\0')
+		goto retry;
+
+	trailing_linefeed = strchr(i->line, '\n');
+	if (trailing_linefeed != NULL)
+		*trailing_linefeed = '\0';
+
+	/*
+	 * Slice the line in two at the colon, if any.  If there is anything
+	 * past the ': ', this is a composite module.  (We allow for no colon
+	 * for robustness, even though one should always be present.)
+	 */
+	if (strchr(i->line, ':') != NULL) {
+		char *name_start;
+
+		object_name = strchr(i->line, ':');
+		*object_name = '\0';
+		object_name++;
+		name_start = object_name + strspn(object_name, " \n");
+		if (*name_start != '\0') {
+			composite = 1;
+			object_name = name_start;
+		}
+	}
+
+	/*
+	 * Figure out the module name.
+	 */
+	last_slash = strrchr(i->line, '/');
+	last_slash = (!last_slash) ? i->line :
+		last_slash + 1;
+	free(*module_name);
+	*module_name = strdup(last_slash);
+	dash = *module_name;
+
+	while (dash != NULL) {
+		dash = strchr(dash, '-');
+		if (dash != NULL)
+			*dash = '_';
+	}
+
+	last_dot = strrchr(*module_name, '.');
+	if (last_dot != NULL)
+		*last_dot = '\0';
+
+	/*
+	 * Multifile separator? Object file names explicitly stated:
+	 * slice them up and shuffle them in.
+	 *
+	 * The array size may be an overestimate if any object file
+	 * names start or end with spaces (very unlikely) but cannot be
+	 * an underestimate.  (Check for it anyway.)
+	 */
+	if (composite) {
+		char *one_object;
+
+		for (npaths = 0, one_object = object_name;
+		     one_object != NULL;
+		     npaths++, one_object = strchr(one_object + 1, ' '));
+	}
+
+	module_paths = malloc((npaths + 1) * sizeof(char *));
+	if (!module_paths) {
+		fprintf(stderr, "%s: out of memory on module %s\n", __func__,
+			*module_name);
+		exit(1);
+	}
+
+	if (composite) {
+		char *one_object;
+		size_t i = 0;
+
+		while ((one_object = strsep(&object_name, " ")) != NULL) {
+			if (i >= npaths) {
+				fprintf(stderr, "%s: num_objs overflow on module "
+					"%s: this is a bug.\n", __func__,
+					*module_name);
+				exit(1);
+			}
+
+			module_paths[i++] = one_object;
+		}
+	} else
+		module_paths[0] = i->line;	/* untransformed module name */
+
+	module_paths[npaths] = NULL;
+
+	return module_paths;
+}
+
+/*
+ * Free an iterator. Can be called while iteration is underway, so even
+ * state that is freed at the end of iteration must be freed here too.
+ */
+void
+modules_builtin_iter_free(struct modules_builtin_iter *i)
+{
+	if (i == NULL)
+		return;
+	fclose(i->f);
+	free(i->line);
+	free(i);
+}

@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A simple modules.builtin.objs reader.
+ *
+ * (C) 2014, 2022 Oracle, Inc.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#ifndef _LINUX_MODULES_BUILTIN_H
+#define _LINUX_MODULES_BUILTIN_H
+
+#include <stdio.h>
+#include <stddef.h>
+
+/*
+ * modules.builtin.objs iteration state.
+ */
+struct modules_builtin_iter {
+	FILE *f;
+	char *line;
+	size_t line_size;
+};
+
+/*
+ * Construct a modules_builtin.objs iterator.
+ */
+struct modules_builtin_iter *
+modules_builtin_iter_new(const char *modules_builtin_file);
+
+/*
+ * Iterate, returning a new null-terminated array of object file names, and a
+ * new dynamically-allocated module name.  (The module name passed in is freed.)
+ *
+ * The array of object file names should be freed by the caller: the strings it
+ * points to are owned by the iterator, and should not be freed.
+ */
+
+char ** __attribute__((__nonnull__))
+modules_builtin_iter_next(struct modules_builtin_iter *i, char **module_name);
+
+void
+modules_builtin_iter_free(struct modules_builtin_iter *i);
+
+#endif