diff options
| -rw-r--r-- | arch/x86/include/asm/msr.h | 24 |
1 files changed, 13 insertions, 11 deletions
diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h index 2ccc78ebc3d7..27bc0b54d0cb 100644 --- a/arch/x86/include/asm/msr.h +++ b/arch/x86/include/asm/msr.h @@ -37,20 +37,22 @@ struct saved_msrs { }; /* - * both i386 and x86_64 returns 64-bit value in edx:eax, but gcc's "A" - * constraint has different meanings. For i386, "A" means exactly - * edx:eax, while for x86_64 it doesn't mean rdx:rax or edx:eax. Instead, - * it means rax *or* rdx. + * Both i386 and x86_64 returns 64-bit values in edx:eax for certain + * instructions, but GCC's "A" constraint has different meanings. + * For i386, "A" means exactly edx:eax, while for x86_64 it + * means rax *or* rdx. + * + * These helpers wrapping these semantic differences save one instruction + * clearing the high half of 'low': */ #ifdef CONFIG_X86_64 -/* Using 64-bit values saves one instruction clearing the high half of low */ -#define DECLARE_ARGS(val, low, high) unsigned long low, high -#define EAX_EDX_VAL(val, low, high) ((low) | (high) << 32) -#define EAX_EDX_RET(val, low, high) "=a" (low), "=d" (high) +# define DECLARE_ARGS(val, low, high) unsigned long low, high +# define EAX_EDX_VAL(val, low, high) ((low) | (high) << 32) +# define EAX_EDX_RET(val, low, high) "=a" (low), "=d" (high) #else -#define DECLARE_ARGS(val, low, high) u64 val -#define EAX_EDX_VAL(val, low, high) (val) -#define EAX_EDX_RET(val, low, high) "=A" (val) +# define DECLARE_ARGS(val, low, high) u64 val +# define EAX_EDX_VAL(val, low, high) (val) +# define EAX_EDX_RET(val, low, high) "=A" (val) #endif /* |