diff options
Diffstat (limited to 'sysdeps/x86_64')
| -rw-r--r-- | sysdeps/x86_64/fpu_control.h | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/sysdeps/x86_64/fpu_control.h b/sysdeps/x86_64/fpu_control.h index 61bc30e973..605302c09b 100644 --- a/sysdeps/x86_64/fpu_control.h +++ b/sysdeps/x86_64/fpu_control.h @@ -1,5 +1,5 @@ -/* FPU control word bits. x86-64 version. - Copyright (C) 1993,1995,1996,1997,1998,2000,2001,2002 Free Software Foundation, Inc. +/* FPU control word bits. x86 version. + Copyright (C) 1993-2012 Free Software Foundation, Inc. This file is part of the GNU C Library. Contributed by Olaf Flebbe. @@ -90,9 +90,18 @@ /* Type of the control word. */ typedef unsigned int fpu_control_t __attribute__ ((__mode__ (__HI__))); -/* Macros for accessing the hardware control word. */ -#define _FPU_GETCW(cw) __asm__ ("fnstcw %0" : "=m" (*&cw)) -#define _FPU_SETCW(cw) __asm__ ("fldcw %0" : : "m" (*&cw)) +/* Macros for accessing the hardware control word. "*&" is used to + work around a bug in older versions of GCC. __volatile__ is used + to support combination of writing the control register and reading + it back. Without __volatile__, the old value may be used for reading + back under compiler optimization. + + Note that the use of these macros is not sufficient anymore with + recent hardware nor on x86-64. Some floating point operations are + executed in the SSE/SSE2 engines which have their own control and + status register. */ +#define _FPU_GETCW(cw) __asm__ __volatile__ ("fnstcw %0" : "=m" (*&cw)) +#define _FPU_SETCW(cw) __asm__ __volatile__ ("fldcw %0" : : "m" (*&cw)) /* Default control word set at startup. */ extern fpu_control_t __fpu_control; |