libc, rtld: translate osreldate to a FreeBSD version for ABI checks

lib/libc/gen/Makefile.inc

@@ -8,6 +8,7 @@ CONFSMODE_master.passwd=	600
 CONFSPACKAGE=   runtime
 
 SRCS+=	__getosreldate.c \
+	__osrel_freebsd.c \
 	__pthread_mutex_init_calloc_cb_stub.c \
 	__xuname.c \
 	_once_stub.c \

lib/libc/gen/__getosreldate.c

@@ -40,6 +40,9 @@
  *
  * Use getosreldate(3) for public use as it respects the $OSVERSION environment
  * variable.
+ *
+ * The kernel reports a MidnightBSD version, but callers compare the result
+ * against FreeBSD versions, so it is translated by __osrel_to_freebsd().
  */
 
 int
@@ -53,16 +56,19 @@ __getosreldate(void)
 	if (osreldate != 0)
 		return (osreldate);
 
-	error = _elf_aux_info(AT_OSRELDATE, &osreldate, sizeof(osreldate));
-	if (error == 0 && osreldate != 0)
+	osrel = 0;
+	error = _elf_aux_info(AT_OSRELDATE, &osrel, sizeof(osrel));
+	if (error == 0 && osrel != 0) {
+		osreldate = __osrel_to_freebsd(osrel);
 		return (osreldate);
+	}
 
 	oid[0] = CTL_KERN;
 	oid[1] = KERN_OSRELDATE;
 	osrel = 0;
 	len = sizeof(osrel);
 	error = sysctl(oid, 2, &osrel, &len, NULL, 0);
 	if (error == 0 && osrel > 0 && len == sizeof(osrel))
-		osreldate = osrel;
+		osreldate = __osrel_to_freebsd(osrel);
 	return (osreldate);
 }

lib/libc/gen/__osrel_freebsd.c

@@ -0,0 +1,87 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2026 The MidnightBSD Project
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/param.h>
+
+#include "libc_private.h"
+
+/*
+ * The kernel reports __MidnightBSD_version as its osreldate, but libc and
+ * rtld compare the value returned by __getosreldate() against FreeBSD
+ * version thresholds (INO64_FIRST, P_OSREL_*, ...).  Translate a
+ * MidnightBSD version to the __FreeBSD_version of the tree that release
+ * was built from, so those checks see the features the kernel really has.
+ *
+ * Each entry is the first MidnightBSD version with that FreeBSD version.
+ * Where one MidnightBSD version spanned several FreeBSD versions, the
+ * lowest is used, so a feature is never assumed before it existed.  Keep
+ * this table in sync with sys/sys/param.h when the FreeBSD base changes.
+ */
+static const struct {
+	int	mnbsd;
+	int	fbsd;
+} osrel_map[] = {
+	{ 400001, 1305500 },	/* 4.0 */
+	{ 301006, 1204500 },	/* 3.1 */
+	{ 300003, 1203507 },	/* 3.0 */
+	{ 200000, 1103507 },	/* 2.0 */
+	{ 100001, 1004501 },	/* 1.0 */
+};
+
+/*
+ * MidnightBSD versions are below the oldest FreeBSD version userland still
+ * checks for.  Anything at or above this is already a FreeBSD version (for
+ * example, a jail created with a FreeBSD osreldate) and is returned
+ * unchanged.
+ *
+ * Values below this are always treated as MidnightBSD versions, even
+ * though FreeBSD 4-6 used the same range.  That is safe: this code only
+ * runs in MidnightBSD userland, and a FreeBSD 4-6 jail runs its own libc
+ * and rtld, which never call it.
+ */
+#define	OSREL_FREEBSD_MIN	700000
+
+int
+__osrel_to_freebsd(int osrel)
+{
+	size_t i;
+
+	if (osrel <= 0 || osrel >= OSREL_FREEBSD_MIN)
+		return (osrel);
+
+	/* A kernel at least as new as this libc has everything it knows. */
+	if (osrel >= __MidnightBSD_version)
+		return (__FreeBSD_version);
+
+	for (i = 0; i < nitems(osrel_map); i++) {
+		if (osrel >= osrel_map[i].mnbsd)
+			return (osrel_map[i].fbsd);
+	}
+
+	/* Older than any release with a FreeBSD 10 base. */
+	return (osrel);
+}

lib/libc/include/libc_private.h

@@ -318,6 +318,12 @@ extern void (*__cleanup)(void) __hidden;
  * ignores value of $OSVERSION and caches result.
  */
 int __getosreldate(void);
+
+/*
+ * Translate a MidnightBSD osreldate to the matching __FreeBSD_version, for
+ * comparisons against FreeBSD version thresholds.
+ */
+int __osrel_to_freebsd(int);
 #include <sys/_types.h>
 #include <sys/_sigset.h>
 

lib/libc/tests/gen/Makefile

@@ -13,6 +13,7 @@ ATF_TESTS_C+=		getentropy_test
 ATF_TESTS_C+=		getmntinfo_test
 ATF_TESTS_C+=		glob2_test
 ATF_TESTS_C+=		makecontext_test
+ATF_TESTS_C+=		osrel_freebsd_test
 ATF_TESTS_C+=		popen_test
 ATF_TESTS_C+=		posix_spawn_test
 ATF_TESTS_C+=		realpath2_test
@@ -94,6 +95,11 @@ LIBADD.syslog_test+=	pthread
 
 CFLAGS+=		-I${.CURDIR}
 
+# __osrel_to_freebsd() is private to libc, so build its source into the test.
+.PATH:	${SRCTOP}/lib/libc/gen
+SRCS.osrel_freebsd_test=	osrel_freebsd_test.c __osrel_freebsd.c
+CFLAGS.__osrel_freebsd.c+=	-I${SRCTOP}/lib/libc/include
+
 SRCS.fmtcheck2_test=	fmtcheck_test.c
 SRCS.fnmatch2_test=	fnmatch_test.c
 

lib/libc/tests/gen/osrel_freebsd_test.c

@@ -0,0 +1,111 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2026 The MidnightBSD Project
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * Tests for __osrel_to_freebsd(), which libc and rtld use to turn the
+ * kernel's MidnightBSD osreldate into a FreeBSD version for ABI checks.
+ * The function is private to libc, so its source is built into this test.
+ */
+
+#include <sys/param.h>
+#include <sys/sysctl.h>
+
+#include <atf-c.h>
+
+int __osrel_to_freebsd(int);
+
+/* From lib/libc/sys/compat-ino64.h. */
+#define	INO64_FIRST	1200031
+
+ATF_TC_WITHOUT_HEAD(passthrough);
+ATF_TC_BODY(passthrough, tc)
+{
+	/* Unset, invalid, and values that are already FreeBSD versions. */
+	ATF_CHECK_EQ(__osrel_to_freebsd(0), 0);
+	ATF_CHECK_EQ(__osrel_to_freebsd(-1), -1);
+	ATF_CHECK_EQ(__osrel_to_freebsd(700000), 700000);
+	ATF_CHECK_EQ(__osrel_to_freebsd(1305500), 1305500);
+	ATF_CHECK_EQ(__osrel_to_freebsd(1400000), 1400000);
+
+	/* Older than any release with a FreeBSD 10 base. */
+	ATF_CHECK_EQ(__osrel_to_freebsd(9005), 9005);
+	ATF_CHECK_EQ(__osrel_to_freebsd(100000), 100000);
+}
+
+ATF_TC_WITHOUT_HEAD(table_boundaries);
+ATF_TC_BODY(table_boundaries, tc)
+{
+	ATF_CHECK_EQ(__osrel_to_freebsd(100001), 1004501);
+	ATF_CHECK_EQ(__osrel_to_freebsd(199999), 1004501);
+	ATF_CHECK_EQ(__osrel_to_freebsd(200000), 1103507);
+	ATF_CHECK_EQ(__osrel_to_freebsd(300002), 1103507);
+	ATF_CHECK_EQ(__osrel_to_freebsd(300003), 1203507);
+	ATF_CHECK_EQ(__osrel_to_freebsd(301005), 1203507);
+	ATF_CHECK_EQ(__osrel_to_freebsd(301006), 1204500);
+	ATF_CHECK_EQ(__osrel_to_freebsd(400000), 1204500);
+	ATF_CHECK_EQ(__osrel_to_freebsd(400001), 1305500);
+}
+
+ATF_TC_WITHOUT_HEAD(current_release);
+ATF_TC_BODY(current_release, tc)
+{
+	/* A kernel at least as new as this libc maps to its FreeBSD base. */
+	ATF_CHECK_EQ(__osrel_to_freebsd(__MidnightBSD_version),
+	    __FreeBSD_version);
+	ATF_CHECK_EQ(__osrel_to_freebsd(__MidnightBSD_version + 1),
+	    __FreeBSD_version);
+	ATF_CHECK_EQ(__osrel_to_freebsd(699999), __FreeBSD_version);
+}
+
+ATF_TC_WITHOUT_HEAD(running_kernel);
+ATF_TC_BODY(running_kernel, tc)
+{
+	size_t len;
+	int osrel;
+
+	len = sizeof(osrel);
+	ATF_REQUIRE(sysctlbyname("kern.osreldate", &osrel, &len, NULL, 0) ==
+	    0);
+
+	/*
+	 * The running kernel has the ino64 syscalls, so libc must not fall
+	 * back to the freebsd11 compat versions.
+	 */
+	ATF_CHECK_MSG(__osrel_to_freebsd(osrel) >= INO64_FIRST,
+	    "kern.osreldate %d translates to %d, below INO64_FIRST", osrel,
+	    __osrel_to_freebsd(osrel));
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, passthrough);
+	ATF_TP_ADD_TC(tp, table_boundaries);
+	ATF_TP_ADD_TC(tp, current_release);
+	ATF_TP_ADD_TC(tp, running_kernel);
+
+	return (atf_no_error());
+}

libexec/rtld-elf/rtld-libc/Makefile.inc

@@ -33,7 +33,7 @@ CFLAGS.merge.c+=-Wno-error=null-pointer-arithmetic
 .endif
 .PATH: ${LIBC_SRCTOP}/gen
 SRCS+=	errlst.c getcwd.c getprogname.c raise.c sigsetops.c sysctlnametomib.c \
-    __xuname.c
+    __xuname.c __osrel_freebsd.c
 # errlst.c needs the errlst.h header from libc:
 CFLAGS.errlst.c+=-I${LIBC_SRCTOP}/include
 

libexec/rtld-elf/rtld-libc/rtld_libc.h

@@ -62,6 +62,7 @@ __ssize_t	__sys_write(int, const void *, __size_t);
 extern char* __progname;
 const char *_getprogname(void);
 int __getosreldate(void);
+int __osrel_to_freebsd(int);
 
 
 /*

libexec/rtld-elf/rtld.c

@@ -2424,7 +2424,7 @@ init_rtld(caddr_t mapbase, Elf_Auxinfo **aux_info)
 #endif
 
     if (aux_info[AT_OSRELDATE] != NULL)
-	    osreldate = aux_info[AT_OSRELDATE]->a_un.a_val;
+	    osreldate = __osrel_to_freebsd(aux_info[AT_OSRELDATE]->a_un.a_val);
 
     digest_dynamic2(&obj_rtld, dyn_rpath, dyn_soname, dyn_runpath);
 
@@ -6355,7 +6355,7 @@ __getosreldate(void)
 	len = sizeof(osrel);
 	error = sysctl(oid, 2, &osrel, &len, NULL, 0);
 	if (error == 0 && osrel > 0 && len == sizeof(osrel))
-		osreldate = osrel;
+		osreldate = __osrel_to_freebsd(osrel);
 	return (osreldate);
 }
 const char *