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Re: [PATCH] x86: fix "REP RET" with -madd-bnd-prefix


>>> On 30.05.18 at 14:35, <hjl.tools@gmail.com> wrote:
> On Wed, May 30, 2018 at 12:40 AM, Jan Beulich <JBeulich@suse.com> wrote:
>> --- a/gas/testsuite/gas/i386/x86-64-mpx-add-bnd-prefix.s
>> +++ b/gas/testsuite/gas/i386/x86-64-mpx-add-bnd-prefix.s
>> @@ -8,7 +8,9 @@
>>         jmp     *(%rbx)
>>         ret
>>  foo:
>> -       # Use of REPNE prefix - we shouldn't get any error
>> +       # Use of any REP prefix - we shouldn't get any error
>> +       rep ret
>> +       repe ret
>>         repne ret
>>         # BND prefix already exists - we shouldn't get any error here
>>         bnd ret
>>
> 
> Assembly code asks for F3 prefix and F2 prefix is generated.
> It does't look right to me.

Not emitting a BND prefix despite -madd-bnd-prefix looks even worse
to me: Which REP prefix is used doesn't matter without MPX, but it
very much does matter with MPX.

Jan



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