Message-ID: <fe1662f9-7cab-5f9f-882b-2b8ffa80992c@de.ibm.com>
Date:   Fri, 19 Nov 2021 15:12:03 +0100
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Subject: Re: [PATCH] s390/test_unwind: use raw opcode instead of invalid
 instruction
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To:     Heiko Carstens <hca@linux.ibm.com>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Ilie Halip <ilie.halip@gmail.com>,
        linux-kernel@vger.kernel.org, Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Mete Durlu <meted@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        linux-s390@vger.kernel.org, llvm@lists.linux.dev,
        Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
References: <20211117174822.3632412-1-ilie.halip@gmail.com>
 <CAKwvOd=9tsHHhPBOx2ORZoJP09VsX5dRZn58qj3MzCc2vmVosg@mail.gmail.com>
 <d9ec2704-f41c-eafa-1945-ce845d65be8a@de.ibm.com> <YZeCcSjh4yCzzDcH@osiris>
 <658a63b5-2d18-2837-9639-75a14c959f73@de.ibm.com> <YZeF4JjWIcTMtaaT@osiris>
From:   Christian Borntraeger <borntraeger@de.ibm.com>
In-Reply-To: <YZeF4JjWIcTMtaaT@osiris>
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Am 19.11.21 um 12:09 schrieb Heiko Carstens:
> On Fri, Nov 19, 2021 at 11:57:05AM +0100, Christian Borntraeger wrote:
>>>>>> -                       "       mvcl    %%r1,%%r1\n"
>>>>>> +                       "       .insn e,0x0e11\n"       /* mvcl %%r1,%%r1" */
>>>
>>> Sorry, I disagree with this. As you said above rr would be the correct
>>> format for this instruction. If we go for the e format then we should
>>> also use an instruction with e format.
>>> Which in this case would simply be an illegal opcode, which would be
>>> sufficient for what this code is good for: ".insn e,0x0000".
>>
>> Why not simply use .short then?
> 
> .short bypasses all sanity checks while .insn does not, so I think
> that should be preferred. But I don't care too much.

Heiko,
I am fine with ".insn e,0x0000" and the a changed comment that changes "specification exception" to "operation exception".
Do you want Ilie to resend or simply fixup?