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Mon, 2 Mar 2026 16:02:55 +0000 (GMT) Date: Mon, 2 Mar 2026 17:02:53 +0100 From: Vasily Gorbik To: Heiko Carstens Cc: Alexander Gordeev , Sven Schnelle , Christian Borntraeger , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Subject: Re: [PATCH 2/3] s390/xor: Improve inline assembly constraints Message-ID: References: <20260302133500.1560531-1-hca@linux.ibm.com> <20260302133500.1560531-3-hca@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260302133500.1560531-3-hca@linux.ibm.com> X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=Rp/I7SmK c=1 sm=1 tr=0 ts=69a5b4b4 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=iSRlMUYzGjX7e-hBr40A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzAyMDEzMSBTYWx0ZWRfX4DD7kkNRI8Rl puhVxb6I3T2KopFkO7F7HcGH/qmyoln9FWmRBVWR0GA7IUuTeKNU0IY4qe3qBMTYSvFKW1d7dad xXfJ1kUTY4ec2oJhV7A4EDAO29Su57YaKLwi8HjJUfwVgbP+hQ7bdeLlv07HJ44/N2zOx06aQ5h GLGK4I8O0C7vB2K3jK8HOUWwTaS5Ze+im79SDQMUeRooBs3mSCaRRqGBQz5KbrLH+nq67hol3IK z4O8mVJRpnYhesrgbmmj0r7si/aW8HID4Fbn+hUm8mNIUAxJUudxmp2QwKBqgDTVuFd30kpioym C8Dm+2wUq/YF8WZyyDZQQF93n1M9jMNQI2aoWWdOZLh7XYopgCgHtlwVf6kfiTFmw40ysWKX1WJ bqOwqs7lhSsjxOEnItHKlMJQ01Exxp8JLgwC5pDDNTCi6XtWPjPAKyyzTHEcNFA2j05v2dslIA/ dRpCPFoFrq6Sx+0z4uQ== X-Proofpoint-GUID: DpNh5UNWGqWAGxSK7U5X5LPUTfJei0NW X-Proofpoint-ORIG-GUID: DpNh5UNWGqWAGxSK7U5X5LPUTfJei0NW X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-02_03,2026-03-02_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 priorityscore=1501 spamscore=0 phishscore=0 adultscore=0 bulkscore=0 clxscore=1015 impostorscore=0 malwarescore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603020131 On Mon, Mar 02, 2026 at 02:34:59PM +0100, Heiko Carstens wrote: > The inline assembly constraint for the "bytes" operand is "d" for all xor() > inline assemblies. "d" means that any register from 0 to 15 can be used. If > the compiler would use register 0 then the exrl instruction would not or > the value of "bytes" into the executed instruction - resulting in an > incorrect result. > > However all the xor() inline assemblies make hard-coded use of register 0, > and it is correctly listed in the clobber list, so that this cannot happen. > > Given that this is quite subtle use the better "a" constraint, which > excludes register 0 from register allocation in any case. > > Signed-off-by: Heiko Carstens > --- > arch/s390/lib/xor.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) Reviewed-by: Vasily Gorbik