libsys, libc: provide rfork_thread() and pdrfork_thread() on all arches

Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D54898

lib/libsys/Symbol.sys.map

@@ -182,6 +182,7 @@ FBSD_1.0 {
 	rename;
 	revoke;
 	rfork;
+	rfork_thread;
 	rmdir;
 	rtprio;
 	rtprio_thread;
@@ -391,6 +392,7 @@ FBSD_1.8 {
 
 FBSD_1.9 {
 	pdrfork;
+	pdrfork_thread;
 };
 
 FBSDprivate_1.0 {

lib/libsys/aarch64/Makefile.sys

@@ -1,6 +1,8 @@
 MIASM:=	${MIASM:Nfreebsd[467]_*}
 
 SRCS+=	__vdso_gettc.c \
+	pdrfork_thread_gen.c \
+	rfork_thread_gen.c \
 	sched_getcpu_gen.c
 
 MDASM=	cerror.S \

lib/libsys/amd64/Symbol.sys.map

@@ -1,5 +1,4 @@
 FBSD_1.0 {
-	rfork_thread;
 	amd64_get_fsbase;
 	amd64_get_gsbase;
 	amd64_set_fsbase;
@@ -17,10 +16,6 @@ FBSD_1.8 {
 	amd64_set_tlsbase;
 };
 
-FBSD_1.9 {
-	pdrfork_thread;
-};
-
 FBSDprivate_1.0 {
 	_vfork;
 };

lib/libsys/arm/Makefile.sys

@@ -1,4 +1,6 @@
 SRCS+=	__vdso_gettc.c \
+	pdrfork_thread_gen.c \
+	rfork_thread_gen.c \
 	sched_getcpu_gen.c
 
 MDASM= \

lib/libsys/i386/Symbol.sys.map

@@ -10,7 +10,6 @@ FBSD_1.0 {
 	i386_set_ldt;
 	i386_set_watch;
 	i386_vm86;
-	rfork_thread;
 };
 
 FBSD_1.6 {
@@ -20,10 +19,6 @@ FBSD_1.6 {
 	 x86_pkru_unprotect_range;
 };
 
-FBSD_1.9 {
-	pdrfork_thread;
-};
-
 FBSDprivate_1.0 {
 	_vfork;
 };

lib/libsys/pdrfork_thread_gen.c

@@ -0,0 +1,34 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright 2026 The FreeBSD Foundation
+ *
+ * This software were developed by
+ * Konstantin Belousov <kib@FreeBSD.org> under sponsorship from
+ * the FreeBSD Foundation.
+ */
+
+#include <sys/types.h>
+#include <sys/procdesc.h>
+#include <errno.h>
+#include <unistd.h>
+
+pid_t
+pdrfork_thread(int *fdp, int pdflags, int rfflags, void *stack_addr,
+    int (*start_fn)(void *), void *arg)
+{
+	pid_t res;
+	int ret;
+
+	/* See comment in rfork_thread_gen.c. */
+	if (stack_addr != NULL) {
+		errno = EOPNOTSUPP;
+		return (-1);
+	}
+	res = pdrfork(fdp, pdflags, rfflags);
+	if (res == 0) {
+		ret = start_fn(arg);
+		_exit(ret);
+	}
+	return (res);
+}

lib/libsys/powerpc/Makefile.sys

@@ -1,4 +1,6 @@
 SRCS+=	__vdso_gettc.c \
+	pdrfork_thread_gen.c \
+	rfork_thread_gen.c \
 	sched_getcpu_gen.c
 
 MDASM+=	cerror.S

lib/libsys/powerpc64/Makefile.sys

@@ -1,4 +1,6 @@
 SRCS+=	__vdso_gettc.c \
+	pdrfork_thread_gen.c \
+	rfork_thread_gen.c \
 	sched_getcpu_gen.c
 
 MDASM+=	cerror.S

lib/libsys/rfork_thread_gen.c

@@ -0,0 +1,40 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright 2026 The FreeBSD Foundation
+ *
+ * This software were developed by
+ * Konstantin Belousov <kib@FreeBSD.org> under sponsorship from
+ * the FreeBSD Foundation.
+ */
+
+#include <errno.h>
+#include <unistd.h>
+
+pid_t
+rfork_thread(int flags, void *stack_addr, int (*start_fn)(void *), void *arg)
+{
+	pid_t res;
+	int ret;
+
+	/*
+	 * Generic implementation cannot switch stacks.  Only
+	 * architecture-specific code knows how to do it.  Require
+	 * that caller knows that, and refuse to do operate if the
+	 * stack was supplied.
+	 *
+	 * Note that implementations that do switch stack, would fault
+	 * immediately if the passed stack is NULL.  They do not need to
+	 * specifically check for the NULL stack value.
+	 */
+	if (stack_addr != NULL) {
+		errno = EOPNOTSUPP;
+		return (-1);
+	}
+	res = rfork(flags);
+	if (res == 0) {
+		ret = start_fn(arg);
+		_exit(ret);
+	}
+	return (res);
+}

lib/libsys/riscv/Makefile.sys

@@ -1,4 +1,6 @@
 SRCS+=	__vdso_gettc.c \
+	pdrfork_thread_gen.c \
+	rfork_thread_gen.c \
 	sched_getcpu_gen.c
 
 MDASM=	cerror.S \