Commit 7753a3a6 authored by Adam Langley's avatar Adam Langley Committed by Ben Laurie
Browse files

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.
parent 5dcd2deb

crypto/bn/asm/x86_64-gcc.c

+4 −4
Original line number Original line Diff line number Diff line
@@ -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;