From 81b115ec2346a8130073e691c83165da9fbb37fb Mon Sep 17 00:00:00 2001 From: Adam Langley Date: Mon, 3 Jun 2013 15:45:11 -0400 Subject: [PATCH 06/11] asm_volatile 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. --- crypto/bn/asm/x86_64-gcc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/crypto/bn/asm/x86_64-gcc.c b/crypto/bn/asm/x86_64-gcc.c index dfb7506..7d97c0b 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; -- 1.8.2.1