The fast syscall path clobbers 2 registers. Which is fine for a plain

system call, as long as the stub knows about it. However, it's bad
for sigreturn. Hence, use the old entry point for sigreturn. XXX

lib/libc/arch/x86_64/sys/__sigtramp1.S

@@ -1,4 +1,4 @@
-/*	$NetBSD: __sigtramp1.S,v 1.2 2002/07/14 12:29:59 fvdl Exp $	*/
+/*	$NetBSD: __sigtramp1.S,v 1.3 2002/12/13 17:43:02 fvdl Exp $	*/
 
 /*
  * Copyright (c) 2001 Wasabi Systems, Inc.
@@ -49,6 +49,6 @@ NENTRY(__sigtramp_sigcontext_1)
 	movq	%rsp,%rdi
 	pushq	%rdi			/* fake return address */
 	movq	$SYS___sigreturn14,%rax
-	syscall
+	int	$0x80			/* to avoid clobbering registers */
 	movq	$SYS_exit,%rax
 	syscall