From: Jan Beulich <jbeulich@suse.com>
Date: Thu, 26 Sep 2013 08:11:00 +0000 (+0200)
Subject: x86: fix rdrand asm()
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~6275
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=573fd5bd2d8bd068a6cea7ae5fcc58b962d43a78;p=xen.git

x86: fix rdrand asm()

Just learned the hard way that at least for non-volatile asm()s gcc
indeed does what the documentation says: It may move it across jumps
(i.e. ahead of the cpu_has() check). While the documentation claims
that this can also happen for volatile asm()s, if that was the case
we'd have many more problems in our code (and e,g, Linux would too).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Keir Fraser <keir@xen.org>
---

diff --git a/xen/include/asm-x86/random.h b/xen/include/asm-x86/random.h
index 6198e72a7b..9e1fe0bc1d 100644
--- a/xen/include/asm-x86/random.h
+++ b/xen/include/asm-x86/random.h
@@ -8,7 +8,7 @@ static inline unsigned int arch_get_random(void)
     unsigned int val = 0;
 
     if ( cpu_has(&current_cpu_data, X86_FEATURE_RDRAND) )
-        asm ( ".byte 0x0f,0xc7,0xf0" : "+a" (val) );
+        asm volatile ( ".byte 0x0f,0xc7,0xf0" : "+a" (val) );
 
     return val;
 }