From: Adam Langley <agl@chromium.org>
Date: Mon, 3 Jun 2013 19:45:11 +0000 (-0400)
Subject: Add volatile qualifications to two blocks of inline asm to stop GCC from
X-Git-Tag: OpenSSL_1_0_2-beta1~76
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=45d010255fc19cce5fd7d509d27c499da06bdd17;p=oweals%2Fopenssl.git

Add volatile qualifications to two blocks of inline asm to stop GCC from
eliminating them as dead code.

Both volatile and "memory" are used because of some concern that the compiler
may still cache values across the asm block without it, and because this was
such a painful debugging session that I wanted to ensure that it's never
repeated.
(cherry picked from commit 7753a3a68431aa81b82beea4c3f5374b41454679)
---

diff --git a/crypto/bn/asm/x86_64-gcc.c b/crypto/bn/asm/x86_64-gcc.c
index dfb7506267..7d97c0bedc 100644
--- a/crypto/bn/asm/x86_64-gcc.c
+++ b/crypto/bn/asm/x86_64-gcc.c
@@ -189,7 +189,7 @@ BN_ULONG bn_add_words (BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,int
 
 	if (n <= 0) return 0;
 
-	asm (
+	asm volatile (
 	"	subq	%0,%0		\n"	/* clear carry */
 	"	jmp	1f		\n"
 	".p2align 4			\n"
@@ -201,7 +201,7 @@ BN_ULONG bn_add_words (BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,int
 	"	sbbq	%0,%0		\n"
 		: "=&r"(ret),"+c"(n),"+r"(i)
 		: "r"(rp),"r"(ap),"r"(bp)
-		: "cc"
+		: "cc", "memory"
 	);
 
   return ret&1;
@@ -214,7 +214,7 @@ BN_ULONG bn_sub_words (BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,int
 
 	if (n <= 0) return 0;
 
-	asm (
+	asm volatile (
 	"	subq	%0,%0		\n"	/* clear borrow */
 	"	jmp	1f		\n"
 	".p2align 4			\n"
@@ -226,7 +226,7 @@ BN_ULONG bn_sub_words (BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,int
 	"	sbbq	%0,%0		\n"
 		: "=&r"(ret),"+c"(n),"+r"(i)
 		: "r"(rp),"r"(ap),"r"(bp)
-		: "cc"
+		: "cc", "memory"
 	);
 
   return ret&1;