1 files changed, 101 insertions, 0 deletions
diff --git a/lib/libsys/i386/pdrfork_thread.S b/lib/libsys/i386/pdrfork_thread.S
new file mode 100644
index 000000000000..92a45fc4783f
--- /dev/null
+++ b/lib/libsys/i386/pdrfork_thread.S
@@ -0,0 +1,101 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright 2000 Peter Wemm <peter@FreeBSD.org>
+ * Copyright 2026 The FreeBSD Foundation
+ * All rights reserved.
+ *
+ * Portions of this software were developed by
+ * Konstantin Belousov <kib@FreeBSD.org> under sponsorship from
+ * the FreeBSD Foundation.
+ */
+
+#include <machine/asm.h>
+/*
+ * With thanks to John Dyson for the original version of this.
+ */
+
+#include <SYS.h>
+
+/*
+ *              8    12      16       20          24         28
+ * rfork_thread(fdp, pdflags rfflags, stack_addr, start_fnc, start_arg);
+ *
+ * fdp			Pointer for the resulting fd location
+ * pdflags		Flags as to pdfork.
+ * rfflags:		Flags as to rfork.
+ * stack_addr:		Top of stack for thread.
+ * start_fnc:		Address of thread function to call in child.
+ * start_arg:		Argument to pass to the thread function in child.
+ */
+
+ENTRY(pdrfork_thread)
+	pushl	%ebp
+	movl	%esp, %ebp
+	pushl	%esi
+
+	/*
+	 * Push thread info onto the new thread's stack
+	 */
+	movl	20(%ebp), %esi	# get stack addr
+
+	subl	$4, %esi
+	movl	28(%ebp), %eax	# get start argument
+	movl	%eax, (%esi)
+
+	subl	$4, %esi
+	movl	24(%ebp), %eax	# get start thread address
+	movl	%eax, (%esi)
+
+	/*
+	 * Prepare and execute the thread creation syscall
+	 */
+	pushl	16(%ebp)
+	pushl	12(%ebp)
+	pushl	8(%ebp)
+	pushl	$0
+	_SYSCALL(pdrfork)
+	jb 	2f
+
+	/*
+	 * Check to see if we are in the parent or child
+	 */
+	cmpl	$0, %edx
+	jnz	1f
+	addl	$16, %esp
+	popl	%esi
+	movl	%ebp, %esp
+	popl	%ebp
+	ret
+	.p2align 2
+
+	/*
+	 * If we are in the child (new thread), then
+	 * set-up the call to the internal subroutine.  If it
+	 * returns, then call __exit.
+	 */
+1:
+	movl	%esi,%esp
+	popl	%eax
+	call	*%eax
+	addl	$4, %esp
+
+	/*
+	 * Exit system call
+	 */
+	pushl	%eax
+	pushl	$0
+	_SYSCALL(exit)
+
+	/*
+	 * Branch here if the thread creation fails:
+	 */
+2:
+	addl	$16, %esp
+	popl	%esi
+	movl	%ebp, %esp
+	popl	%ebp
+	jmp	HIDENAME(cerror)
+END(pdrfork_thread)
+
+	.section .note.GNU-stack,"",%progbits