--- /usr/src/sys/sys/cdefs.h	Wed Dec  5 12:00:35 2007
+++ sys/sys/cdefs.h	Wed Dec 19 21:58:24 2007
@@ -403,7 +403,10 @@
  */
 #ifndef	__FBSDID
 #if !defined(lint) && !defined(STRIP_FBSDID)
-#define	__FBSDID(s)	__IDSTRING(__CONCAT(__rcsid_,__LINE__),s)
+#define	__FBSDID_VARNAME	__CONCAT(__srcid_, __LINE__)
+#define	__FBSDID(s)					\
+	static const char __FBSDID_VARNAME [] = #s;	\
+	DATA_SET(srcid_strs, __FBSDID_VARNAME)
 #else
 #define	__FBSDID(s)	struct __hack
 #endif
@@ -557,5 +560,11 @@
 #define	__ISO_C_VISIBLE		1999
 #endif
 #endif
+
+/*
+ * Since linker_set.h requires cdefs.h (this file) and macros defined in here,
+ * include it at the end.
+ */
+#include <sys/linker_set.h>
 
 #endif /* !_SYS_CDEFS_H_ */
--- /usr/src/sys/kern/kern_mib.c	Wed Dec  5 12:00:30 2007
+++ sys/kern/kern_mib.c	Tue Dec 18 01:19:03 2007
@@ -38,6 +38,7 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD: src/sys/kern/kern_mib.c,v 1.85 2007/12/04 12:28:07 kib Exp $");
 
+#include "opt_ddb.h"
 #include "opt_posix.h"
 #include "opt_config.h"
 
@@ -307,6 +308,85 @@
 SYSCTL_PROC(_kern, KERN_SECURELVL, securelevel,
     CTLTYPE_INT|CTLFLAG_RW|CTLFLAG_PRISON, 0, 0, sysctl_kern_securelvl,
     "I", "Current secure level");
+
+/*
+ * We're going to use __start* and __end magic symbols brought to us by
+ * gcc(1).
+ */
+SET_DECLARE(srcid_strs, const char);
+
+/*
+ * Based on __FBSDID format, skip common parts that bring no valueable
+ * information in this context.
+ */
+static void
+srcid_fname(const char *id, const char **ret, int *retlen)
+{
+	const char *p = NULL;
+	int l = 0;
+
+	KASSERT(id != NULL, ("id == NULL"));
+	KASSERT(ret != NULL, ("p == NULL"));
+	KASSERT(retlen != NULL, ("len == NULL"));
+
+	p = strstr(id, "$FreeBSD: ");
+	if (p != NULL)
+		id += strlen("$FreeBSD: ");
+	l = strlen(id);
+	p = strstr(id, " Exp $");
+	if (p != NULL)
+		l = p - id;
+	*ret = id;
+	*retlen = l;
+}
+
+/*
+ * Return all __FBSDID tags. The output is huge.
+ */
+static int
+sysctl_kern_srcids(SYSCTL_HANDLER_ARGS)
+{
+	struct sbuf *sb;
+	const char **ids;
+	const char *id;
+	int error, olen;
+	const char *p;
+
+	sb = sbuf_new(NULL, NULL, 4096, SBUF_AUTOEXTEND);
+	if (sb == NULL)
+		return (ENOMEM);
+	sbuf_clear(sb);
+	SET_FOREACH(ids, srcid_strs) {
+		id = *ids;
+		srcid_fname(id, &p, &olen);
+		sbuf_printf(sb, "\n%.*s", olen, p);
+	}
+	sbuf_finish(sb);
+	error = sysctl_handle_string(oidp, sbuf_data(sb),
+	    sbuf_len(sb), req);
+	sbuf_delete(sb);
+	return (error);
+}
+SYSCTL_PROC(_kern, OID_AUTO, srcids, CTLTYPE_STRING|CTLFLAG_RD, 0, 0,
+    sysctl_kern_srcids, "A", "Revision control tags for kernel sources");
+
+#ifdef DDB
+#include <ddb/ddb.h>
+
+DB_SHOW_COMMAND(srcids, db_srcid_list)
+{
+	const char **ids;
+	const char *id;
+	const char *p;
+	int olen;
+
+	SET_FOREACH(ids, srcid_strs) {
+		id = *ids;
+		srcid_fname(id, &p, &olen);
+		db_printf("%.*s\n", olen, p);
+	}
+}
+#endif
 
 #ifdef INCLUDE_CONFIG_FILE
 /* Actual kernel configuration options. */