diff options
Diffstat (limited to 'arch/x86/include/asm/asm.h')
| -rw-r--r-- | arch/x86/include/asm/asm.h | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h index eef0771512de..f963848024a5 100644 --- a/arch/x86/include/asm/asm.h +++ b/arch/x86/include/asm/asm.h @@ -238,5 +238,24 @@ register unsigned long current_stack_pointer asm(_ASM_SP); #define _ASM_EXTABLE_FAULT(from, to) \ _ASM_EXTABLE_TYPE(from, to, EX_TYPE_FAULT) +/* + * 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 +# define EAX_EDX_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 EAX_EDX_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 + #endif /* __KERNEL__ */ #endif /* _ASM_X86_ASM_H */ |