Commit 7180d4fb authored by Jan Beulich's avatar Jan Beulich Committed by Linus Torvalds
Browse files

[PATCH] x86_64: Fix 64bit FXSAVE encoding 



The separation of the rex64 prefix (on fxsave/fxrstor) by way of using
a semicolon resulted in the prefix not always taking effect (because
when extended registers are needed for addressing, another rex prefix
would have been generated by the compiler), thus (depending on the
build) resulting in eventually getting 32-bit saves and/or restores.

Signed-Off-By: default avatarJan Beulich <jbeulich@novell.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e9928674

include/asm-x86_64/i387.h

+48 −10
Original line number Diff line number Diff line
@@ -75,7 +75,8 @@ extern int set_fpregs(struct task_struct *tsk, 
static inline int restore_fpu_checking(struct i387_fxsave_struct *fx) 

{ 

	int err;

	asm volatile("1:  rex64 ; fxrstor (%[fx])\n\t"



	asm volatile("1:  rex64/fxrstor (%[fx])\n\t"

		     "2:\n"

		     ".section .fixup,\"ax\"\n"

		     "3:  movl $-1,%[err]\n"
@@ -86,7 +87,11 @@ static inline int restore_fpu_checking(struct i387_fxsave_struct *fx) 
		     "   .quad  1b,3b\n"

		     ".previous"

		     : [err] "=r" (err)

		     : [fx] "r" (fx), "0" (0)); 

#if 0 /* See comment in __fxsave_clear() below. */

		     : [fx] "r" (fx), "m" (*fx), "0" (0));

#else

		     : [fx] "cdaSDb" (fx), "m" (*fx), "0" (0));

#endif

	if (unlikely(err))

		init_fpu(current);

	return err;
@@ -95,7 +100,8 @@ static inline int restore_fpu_checking(struct i387_fxsave_struct *fx) 
static inline int save_i387_checking(struct i387_fxsave_struct __user *fx) 

{ 

	int err;

	asm volatile("1:  rex64 ; fxsave (%[fx])\n\t"



	asm volatile("1:  rex64/fxsave (%[fx])\n\t"

		     "2:\n"

		     ".section .fixup,\"ax\"\n"

		     "3:  movl $-1,%[err]\n"
@@ -105,20 +111,53 @@ static inline int save_i387_checking(struct i387_fxsave_struct __user *fx) 
		     "   .align 8\n"

		     "   .quad  1b,3b\n"

		     ".previous"

		     : [err] "=r" (err)

		     : [err] "=r" (err), "=m" (*fx)

#if 0 /* See comment in __fxsave_clear() below. */

		     : [fx] "r" (fx), "0" (0));

#else

		     : [fx] "cdaSDb" (fx), "0" (0));

#endif

	if (unlikely(err))

		__clear_user(fx, sizeof(struct i387_fxsave_struct));

	return err;

} 



static inline void __fxsave_clear(struct task_struct *tsk)

{

	/* Using "rex64; fxsave %0" is broken because, if the memory operand

	   uses any extended registers for addressing, a second REX prefix

	   will be generated (to the assembler, rex64 followed by semicolon

	   is a separate instruction), and hence the 64-bitness is lost. */

#if 0

	/* Using "fxsaveq %0" would be the ideal choice, but is only supported

	   starting with gas 2.16. */

	__asm__ __volatile__("fxsaveq %0"

			     : "=m" (tsk->thread.i387.fxsave));

#elif 0

	/* Using, as a workaround, the properly prefixed form below isn't

	   accepted by any binutils version so far released, complaining that

	   the same type of prefix is used twice if an extended register is

	   needed for addressing (fix submitted to mainline 2005-11-21). */

	__asm__ __volatile__("rex64/fxsave %0"

			     : "=m" (tsk->thread.i387.fxsave));

#else

	/* This, however, we can work around by forcing the compiler to select

	   an addressing mode that doesn't require extended registers. */

	__asm__ __volatile__("rex64/fxsave %P2(%1)"

			     : "=m" (tsk->thread.i387.fxsave)

			     : "cdaSDb" (tsk),

				"i" (offsetof(__typeof__(*tsk),

					      thread.i387.fxsave)));

#endif

	__asm__ __volatile__("fnclex");

}



static inline void kernel_fpu_begin(void)

{

	struct thread_info *me = current_thread_info();

	preempt_disable();

	if (me->status & TS_USEDFPU) {

		asm volatile("rex64 ; fxsave %0 ; fnclex"

			      : "=m" (me->task->thread.i387.fxsave));

		__fxsave_clear(me->task);

		me->status &= ~TS_USEDFPU;

		return;

	}
@@ -133,8 +172,7 @@ static inline void kernel_fpu_end(void) 


static inline void save_init_fpu( struct task_struct *tsk )

{

	asm volatile( "rex64 ; fxsave %0 ; fnclex"

		      : "=m" (tsk->thread.i387.fxsave));

 	__fxsave_clear(tsk);

	tsk->thread_info->status &= ~TS_USEDFPU;

	stts();

}

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