I checked in an alternative as changeset 16143.
K.
On 19/10/07 17:59, "Dave Lively" <dlively@xxxxxxxxxxxxxxx> wrote:
> You're right. We don't currently see this behavior since we build
> with frame pointers, so those local variable references are
> %bp-relative instead of %sp-relative. (But -fomit-frame-pointers is
> the default, and this definitely won't work there.)
>
> it seems fairly easy to fix with another stack temp or (better)
> register. But it would be nice to find a solution that doesn't
> require another temp. (I'm looking too ...)
>
> Dave
>
> On 10/19/07, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:
>> Good point! Unfortunately the patch is also subtly wrong. We cannot access
>> the _sav argument while we have unpopped items on the stack. This is because
>> _sav is a memory argument referencing a local variable (hence is on-stack).
>> Hence gcc will probably emit a stack-pointer-relative effective address,
>> which will be incorrect because the stack pointer is different from what gcc
>> expects.
>>
>> I'll have a think about how to fix this one.
>>
>> -- Keir
>>
>> On 19/10/07 16:43, "David Lively" <dlively@xxxxxxxxxxxxxxx> wrote:
>>
>>> The x86_emulate code uses the _PRE_EFLAGS macro to setup eflags
>>> immediately before executing (an emulated version of) the instruction.
>>> But _PRE_EFLAGS ends in a "andl" instruction, which clobbers the real
>>> eflags we've just carefully set up. This fix simply leaves the new
>>> eflags value on the stack until the final "popf" into eflags.
>>>
>>> Signed-off-by: David Lively <dlively@xxxxxxxxxxxxxxx>
>>>
>>> diff -r 85791ff698bd xen/arch/x86/x86_emulate.c
>>> --- a/xen/arch/x86/x86_emulate.c Fri Oct 19 11:31:38 2007 -0400
>>> +++ b/xen/arch/x86/x86_emulate.c Fri Oct 19 11:31:38 2007 -0400
>>> @@ -300,7 +300,7 @@ struct operand {
>>>
>>> /* Before executing instruction: restore necessary bits in EFLAGS. */
>>> #define _PRE_EFLAGS(_sav, _msk, _tmp) \
>>> -/* EFLAGS = (_sav & _msk) | (EFLAGS & ~_msk); */\
>>> +/* push (_sav & _msk) | (EFLAGS & ~_msk); */\
>>> "push %"_sav"; " \
>>> "movl %"_msk",%"_LO32 _tmp"; " \
>>> "andl %"_LO32 _tmp",("_STK"); " \
>>> @@ -309,11 +309,12 @@ struct operand {
>>> "andl %"_LO32 _tmp",("_STK"); " \
>>> "pop %"_tmp"; " \
>>> "orl %"_LO32 _tmp",("_STK"); " \
>>> -"popf; " \
>>> /* _sav &= ~msk; */ \
>>> "movl %"_msk",%"_LO32 _tmp"; " \
>>> "notl %"_LO32 _tmp"; " \
>>> -"andl %"_LO32 _tmp",%"_sav"; "
>>> +"andl %"_LO32 _tmp",%"_sav"; " \
>>> +/* pop EFLAGS */ \
>>> +"popf; "
>>>
>>> /* After executing instruction: write-back necessary bits in EFLAGS. */
>>> #define _POST_EFLAGS(_sav, _msk, _tmp) \
>>> _______________________________________________
>>> Xen-devel mailing list
>>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>>> http://lists.xensource.com/xen-devel
>>
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-devel
>>
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