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Re: [PATCH] X86: Disassemble primary opcode map's group 2 ModRM.reg == 6 aliases correctly


>>> On 30.05.17 at 16:43, <hjl.tools@gmail.com> wrote:
> On Tue, May 30, 2017 at 7:41 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>> On 30.05.17 at 16:35, <hjl.tools@gmail.com> wrote:
>>> On Tue, May 30, 2017 at 1:37 AM, Borislav Petkov <bp@suse.de> wrote:
>>>> On Tue, May 30, 2017 at 02:34:28AM -0600, Jan Beulich wrote:
>>>>> which I think should read
>>>>>
>>>>> "The CF flag contains the value of the last bit shifted out of the
>>>>>  destination operand; for instructions other than SAR it is undefined
>>>>>  when the count is greater than or equal to the size (in bits) of
>>>>>  the destination operand."
>>>>
>>>> Makes sense.
>>>
>>> I look another look.  Disassembler always display "shl".  Please
>>> don't use "sal" now.
>>
>> Which disassembler are you talking about, as you can't mean
>> objdump or anything else that's libopcode-based?
> 
> [hjl@gnu-6 tmp]$ cat x.s
> shl %cl, %eax
> sal %cl, %eax
> shl $1, %eax
> sal $1, %eax
> [hjl@gnu-6 tmp]$ gcc -c x.s
> [hjl@gnu-6 tmp]$ objdump -dw x.o
> 
> x.o:     file format elf64-x86-64
> 
> 
> Disassembly of section .text:
> 
> 0000000000000000 <.text>:
>    0: d3 e0                 shl    %cl,%eax
>    2: d3 e0                 shl    %cl,%eax
>    4: d1 e0                 shl    %eax
>    6: d1 e0                 shl    %eax
> [hjl@gnu-6 tmp]$ objdump -dw -Mintel x.o
> 
> x.o:     file format elf64-x86-64
> 
> 
> Disassembly of section .text:
> 
> 0000000000000000 <.text>:
>    0: d3 e0                 shl    eax,cl
>    2: d3 e0                 shl    eax,cl
>    4: d1 e0                 shl    eax,1
>    6: d1 e0                 shl    eax,1
> [hjl@gnu-6 tmp]$

Right, but here all instructions use the /4 encoding. We're talking
about how to display the /6 encoding, though, and I think it would
be helpful to the user if she could distinguish one from the other
without having to look at the opcode bytes.

Jan


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