On Sun, Aug 8, 2010 at 2:34 PM, Avi Kivity <avi@xxxxxxxxxx> wrote:
> On 08/08/2010 05:27 AM, Mohammed Gamal wrote:
>>
>> This adds unary mul, imul, div, and idiv instructions (group 3 r/m 4-7).
>>
>> Signed-off-by: Mohammed Gamal<m.gamal005@xxxxxxxxx>
>> ---
>> arch/x86/kvm/emulate.c | 41 ++++++++++++++++++++++++++++++++++++++++-
>> 1 files changed, 40 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
>> index 7d78832..6d1ec53 100644
>> --- a/arch/x86/kvm/emulate.c
>> +++ b/arch/x86/kvm/emulate.c
>> @@ -315,6 +315,31 @@ struct group_dual {
>> } \
>> } while (0)
>>
>> +#define __emulate_1op_src(_op, _src, _ax, _dx, _eflags, _suffix)
>> \
>
> Not just 1op - add rax_rdx to the name to indicate these are implicit
> operands.
>
>> + do { \
>> + unsigned long _tmp; \
>> + \
>> + __asm__ __volatile__ ( \
>> + _PRE_EFLAGS("0", "4", "1") \
>> + _op _suffix " %5; " \
>> + _POST_EFLAGS("0", "4", "1") \
>> + : "=m" (_eflags), "=&r" (_tmp), \
>> + "=a" (_ax), "=d" (_dx) \
>> + : "i" (EFLAGS_MASK), "m" ((_src).val), \
>> + "a" (_ax), "d" (_dx)); \
>> + } while (0)
>
> The byte form of the instruction doesn't update dx, and the word form
> doesn't update edx[16:31]. So the "=a" and "=d" operands need to be "+a"
> and "+d" so the compiler loads them before the operation is started.
>
> Please add a test to the effect, for example start with eax=0x12345678, and
> multiply (byte size) 0x80 by 0x40,
We already have a value store in eax, so I can only either multiply it
by 0x80 or 0x40. Or do you mean we should have eax=0x12345680 and then
perhaps multply by 0x40 and make sure the upper 16 bits are preserved?
> and observe that the upper 16 bits of eax
> are preserved (and that rdx is not modified).
>
> --
> I have a truly marvellous patch that fixes the bug which this
> signature is too narrow to contain.
>
>
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