Re: assemble code and disassembled code in-consistency

Re: assemble code and disassembled code in-consistency

[H.J. Lu]

On Fri, Jul 6, 2012 at 9:27 AM, Feng LI <nemokingdom@gmail.com> wrote:
> Hi folks,
>
> I have a backend hook (x86_64) for builtin function expansion, so
> I have this:
>
> expand_simple_binop (DImode, ASHIFT, op0,
>                                 GEN_INT (32),op0,1,OPTAB_DIRECT);
>
> to generate op0 = op0<<32 (op0 is the first argument of this builtin
> function, with type SIZE_T)
>
> The thing goes well in the assemble code, where I got:
>         movq    104(%rbx), %rax
>         salq    $32, %rax
>         addq    80(%rbx), %rax
>
> as expected.
>
> But at execution time, it gives me a strange behavior,
> So I disassemble the code,
>
> 401135:       48 8b 43 68             mov    0x68(%rbx),%rax
> 401140:       48 c1 e0 20             shl    $0x20,%rax
> 401144:       48 03 43 50             add    0x50(%rbx),%rax
>
> and it turns out salq are changed to shl which leads to the
> strange behavior. shl only allows shift less or equal than 31.
>

It is a binutils issue.


-- 
H.J.

Re: assemble code and disassembled code in-consistency

[H.J. Lu]

On Fri, Jul 6, 2012 at 9:47 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Fri, Jul 6, 2012 at 9:27 AM, Feng LI <nemokingdom@gmail.com> wrote:
>> Hi folks,
>>
>> I have a backend hook (x86_64) for builtin function expansion, so
>> I have this:
>>
>> expand_simple_binop (DImode, ASHIFT, op0,
>>                                 GEN_INT (32),op0,1,OPTAB_DIRECT);
>>
>> to generate op0 = op0<<32 (op0 is the first argument of this builtin
>> function, with type SIZE_T)
>>
>> The thing goes well in the assemble code, where I got:
>>         movq    104(%rbx), %rax
>>         salq    $32, %rax
>>         addq    80(%rbx), %rax
>>
>> as expected.
>>
>> But at execution time, it gives me a strange behavior,
>> So I disassemble the code,
>>
>> 401135:       48 8b 43 68             mov    0x68(%rbx),%rax
>> 401140:       48 c1 e0 20             shl    $0x20,%rax
>> 401144:       48 03 43 50             add    0x50(%rbx),%rax
>>
>> and it turns out salq are changed to shl which leads to the
>> strange behavior. shl only allows shift less or equal than 31.
>>
>
> It is a binutils issue.

Hi Peter, Andi, Mark,

For some reason, binutils encodes sal the same as shl.  I'd
like to fix it.  Will it cause any problems?

Thanks.

-- 
H.J.

Re: assemble code and disassembled code in-consistency

[Mark Charney]

On 7/6/12 12:54 PM, H.J. Lu wrote:
> On Fri, Jul 6, 2012 at 9:47 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Fri, Jul 6, 2012 at 9:27 AM, Feng LI <nemokingdom@gmail.com> wrote:
>>> Hi folks,
>>>
>>> I have a backend hook (x86_64) for builtin function expansion, so
>>> I have this:
>>>
>>> expand_simple_binop (DImode, ASHIFT, op0,
>>>                                  GEN_INT (32),op0,1,OPTAB_DIRECT);
>>>
>>> to generate op0 = op0<<32 (op0 is the first argument of this builtin
>>> function, with type SIZE_T)
>>>
>>> The thing goes well in the assemble code, where I got:
>>>          movq    104(%rbx), %rax
>>>          salq    $32, %rax
>>>          addq    80(%rbx), %rax
>>>
>>> as expected.
>>>
>>> But at execution time, it gives me a strange behavior,
>>> So I disassemble the code,
>>>
>>> 401135:       48 8b 43 68             mov    0x68(%rbx),%rax
>>> 401140:       48 c1 e0 20             shl    $0x20,%rax
>>> 401144:       48 03 43 50             add    0x50(%rbx),%rax
>>>
>>> and it turns out salq are changed to shl which leads to the
>>> strange behavior. shl only allows shift less or equal than 31.
>>>
>> It is a binutils issue.
> Hi Peter, Andi, Mark,
>
> For some reason, binutils encodes sal the same as shl.  I'd
> like to fix it.  Will it cause any problems?
>
> Thanks.
>

SAL = SHL functionally. They are aliases. FWIW, XED
does not even have SAL; I call them all SHL.