--- /usr/src/sys/sys/cdefs.h	Wed Dec  5 12:00:35 2007
+++ sys/sys/cdefs.h	Thu Dec 20 01:16:27 2007
@@ -403,7 +403,11 @@
  */
 #ifndef	__FBSDID
 #if !defined(lint) && !defined(STRIP_FBSDID)
-#define	__FBSDID(s)	__IDSTRING(__CONCAT(__rcsid_,__LINE__),s)
+#define	__FBSDID(s)					\
+	__asm__(".section set_srcid,\"a\",@progbits");	\
+	__asm__(".p2align 0");				\
+	__asm__(".asciz " #s );				\
+	__asm__(".previous")
 #else
 #define	__FBSDID(s)	struct __hack
 #endif
--- /usr/src/sys/kern/kern_mib.c	Wed Dec  5 12:00:30 2007
+++ sys/kern/kern_mib.c	Thu Dec 20 01:30:27 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 +308,99 @@
 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 __unused
+srcid_fname(char *id, char **ret, int *retlen)
+{
+	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;
+}
+
+/*
+ * Magic generated by the gcc(1) to mark the section ranges with special
+ * variable names.
+ */
+extern char __start_set_srcid[];
+extern char __stop_set_srcid[];
+
+#define	FBSDID_BEGIN	(&__start_set_srcid[0])
+#define	FBSDID_END	(&__stop_set_srcid[0])
+
+/*
+ * Return all __FBSDID tags. The output is huge.
+ */
+static int
+sysctl_kern_srcids(SYSCTL_HANDLER_ARGS)
+{
+	char *bid = FBSDID_BEGIN;
+	char *eid = FBSDID_END;
+	char *s;
+	int idlen;
+	char *id;
+	int error = 0;
+
+	for (s = bid; s < eid; s++) {
+		srcid_fname(s, &id, &idlen);
+		error = sysctl_handle_opaque(oidp, "\n", 1, req);
+		if (error)
+			break;
+		error = sysctl_handle_opaque(oidp, id, idlen, req);
+		if (error)
+			break;
+		s += strlen(s);
+	}
+	error = sysctl_handle_opaque(oidp, "\0", 1, req);
+	if (error)
+		return (error);
+	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)
+{
+	char *bid = FBSDID_BEGIN;
+	char *eid = FBSDID_END;
+	char *s;
+	int slen;
+	int idlen;
+	char *id;
+
+	for (s = bid; s < eid; s++) {
+		srcid_fname(s, &id, &idlen);
+		db_printf("%.*s\n", idlen, id);
+		slen = strlen(s);
+		s += slen;
+	}
+}
+#endif
 
 #ifdef INCLUDE_CONFIG_FILE
 /* Actual kernel configuration options. */