From 362c6d8dec6dfbedc5717e45769042279a1dd3df Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Thu, 21 Oct 2021 01:42:05 +0300
Subject: [PATCH] nehemiah: manually assemble xstore(-rng)

It seems that clang IAS erronously adds repz prefix which should not be
there.  Cpu would try to store around %ecx bytes of random, while we
only expect a word.

PR:	259218
Reported and tested by:	 Dennis Clarke <dclarke@blastwave.org>
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
---
 sys/dev/random/nehemiah.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sys/dev/random/nehemiah.c b/sys/dev/random/nehemiah.c
index ba0dfb200ba..3ad18005c93 100644
--- a/sys/dev/random/nehemiah.c
+++ b/sys/dev/random/nehemiah.c
@@ -68,7 +68,7 @@ VIA_RNG_store(void *buf)
 #ifdef __GNUCLIKE_ASM
 	__asm __volatile(
 		"movl	$0,%%edx\n\t"
-		"xstore"
+		".byte 0x0f, 0xa7, 0xc0"
 			: "=a" (retval), "+d" (rate), "+D" (buf)
 			:
 			: "memory"