Index: arch/i386/Makefile.inc
===================================================================
RCS file: /cvsroot/src/lib/libc/arch/i386/Makefile.inc,v
retrieving revision 1.21
diff -u -r1.21 Makefile.inc
--- arch/i386/Makefile.inc	15 Jul 2015 14:27:49 -0000	1.21
+++ arch/i386/Makefile.inc	12 Oct 2020 21:10:07 -0000
@@ -3,3 +3,5 @@
 .if ${RUMPRUN} != "yes"
 SRCS+=	__sigaction14_sigtramp.c __sigtramp2.S
 .endif
+
+CPPFLAGS+=	-I.
Index: arch/i386/genassym.cf
===================================================================
RCS file: arch/i386/genassym.cf
diff -N arch/i386/genassym.cf
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ arch/i386/genassym.cf	12 Oct 2020 21:10:07 -0000
@@ -0,0 +1,41 @@
+#	$NetBSD$
+#
+# Copyright (c) 2020 The NetBSD Foundation, Inc.
+# All rights reserved.
+#
+# This code is derived from software contributed to The NetBSD Foundation
+# by Kamil Rytarowski or Moritz Systems Technology Company Sp. z o.o.
+#
+# 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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 <ucontext.h>
+
+define UC_GREGS_EAX offsetof(ucontext_t, uc_mcontext.__gregs[_REG_EAX])
+define UC_GREGS_EDX offsetof(ucontext_t, uc_mcontext.__gregs[_REG_EDX])
+define UC_GREGS_ECX offsetof(ucontext_t, uc_mcontext.__gregs[_REG_ECX])
+define UC_GREGS_EBX offsetof(ucontext_t, uc_mcontext.__gregs[_REG_EBX])
+define UC_GREGS_ESI offsetof(ucontext_t, uc_mcontext.__gregs[_REG_ESI])
+define UC_GREGS_EDI offsetof(ucontext_t, uc_mcontext.__gregs[_REG_EDI])
+define UC_GREGS_EBP offsetof(ucontext_t, uc_mcontext.__gregs[_REG_EBP])
+define UC_GREGS_ESP offsetof(ucontext_t, uc_mcontext.__gregs[_REG_ESP])
+define UC_GREGS_EIP offsetof(ucontext_t, uc_mcontext.__gregs[_REG_EIP])
Index: arch/i386/sys/__sigtramp2.S
===================================================================
RCS file: /cvsroot/src/lib/libc/arch/i386/sys/__sigtramp2.S,v
retrieving revision 1.5
diff -u -r1.5 __sigtramp2.S
--- arch/i386/sys/__sigtramp2.S	23 May 2014 02:34:19 -0000	1.5
+++ arch/i386/sys/__sigtramp2.S	12 Oct 2020 21:10:07 -0000
@@ -30,6 +30,7 @@
  */
 
 #include "SYS.h"
+#include "assym.h"
 
 /*
  * The i386 signal trampoline is invoked only to return from
@@ -42,7 +43,25 @@
  *		pointer to ucontext structure		[8]
  *		pointer to siginfo structure		[4]
  *	sp->	signal number				[0]
+ *
+ * The unwind entry includes the one byte prior to the trampoline
+ * because the unwinder will look up (return PC - 1) while unwinding.
+ * Normally (return PC - 1) computes an address inside the call
+ * instruction that created the child frame, but here there is no call
+ * instruction so we have to manually add padding.
  */
+	.cfi_startproc simple
+	.cfi_signal_frame
+	.cfi_def_cfa eax, 140
+	.cfi_offset eax, UC_GREGS_EAX
+	.cfi_offset ecx, UC_GREGS_ECX
+	.cfi_offset edx, UC_GREGS_EDX
+	.cfi_offset ebx, UC_GREGS_EBX
+	/* The unwinder will use the CFA to restore ESP. */
+	.cfi_offset ebp, UC_GREGS_EBP
+	.cfi_offset esi, UC_GREGS_ESI
+	.cfi_offset edi, UC_GREGS_EDI
+	nop
 NENTRY(__sigtramp_siginfo_2)
 	leal	12+128(%esp),%eax	/* get address of ucontext */
 	movl	%eax,4(%esp)	/* put it in the argument slot */
@@ -50,4 +69,5 @@
 	SYSTRAP(setcontext)	/* do setcontext */
 	movl	$-1,4(%esp)	/* if we return here, something is wrong */
 	SYSTRAP(exit)		/* exit */
+	.cfi_endproc
 END(__sigtramp_siginfo_2)