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Add volatile qualifications to two blocks of inline asm to stop GCC from

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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 7753a3a684)
This commit is contained in:
Adam Langley
2013-06-03 15:45:11 -04:00
committed by Andy Polyakov
parent 7e569022c5
commit 45d010255f
1 changed files with 4 additions and 4 deletions
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8
crypto/bn/asm/x86_64-gcc.c
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@@ -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; if (n <= 0) return 0;
asm ( asm volatile (
" subq %0,%0 \n" /* clear carry */ " subq %0,%0 \n" /* clear carry */
" jmp 1f \n" " jmp 1f \n"
".p2align 4 \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" " sbbq %0,%0 \n"
: "=&r"(ret),"+c"(n),"+r"(i) : "=&r"(ret),"+c"(n),"+r"(i)
: "r"(rp),"r"(ap),"r"(bp) : "r"(rp),"r"(ap),"r"(bp)
: "cc" : "cc", "memory"
); );
return ret&1; 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; if (n <= 0) return 0;
asm ( asm volatile (
" subq %0,%0 \n" /* clear borrow */ " subq %0,%0 \n" /* clear borrow */
" jmp 1f \n" " jmp 1f \n"
".p2align 4 \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" " sbbq %0,%0 \n"
: "=&r"(ret),"+c"(n),"+r"(i) : "=&r"(ret),"+c"(n),"+r"(i)
: "r"(rp),"r"(ap),"r"(bp) : "r"(rp),"r"(ap),"r"(bp)
: "cc" : "cc", "memory"
); );
return ret&1; return ret&1;