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Mon, 6 Nov 2023 09:20:54 +0000 (GMT) Message-ID: <150d34e65cff88b2605e5811f8c583b3adb3275a.camel@linux.ibm.com> Subject: Re: [PATCH 2/4] tests/tcg/s390x: Test CLC with inaccessible second operand From: Ilya Leoshkevich To: Richard Henderson , David Hildenbrand Cc: Thomas Huth , qemu-s390x@nongnu.org, qemu-devel@nongnu.org, Michael Tokarev Date: Mon, 06 Nov 2023 10:20:54 +0100 In-Reply-To: <9963393c-f641-402a-94a1-86e6ef740adf@linaro.org> References: <20231031053718.347100-1-iii@linux.ibm.com> <20231031053718.347100-3-iii@linux.ibm.com> <9963393c-f641-402a-94a1-86e6ef740adf@linaro.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.48.4 (3.48.4-1.fc38) MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: d18qD1h_hYOwu0wiPQeUsI8rcHGlT3Tl X-Proofpoint-GUID: yjene3byd8Kq0ix2GWDCQofG16IARUl2 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.987,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-11-06_07,2023-11-02_03,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 phishscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 clxscore=1015 impostorscore=0 mlxscore=0 mlxlogscore=604 malwarescore=0 spamscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2310240000 definitions=main-2311060080 Received-SPF: pass client-ip=148.163.158.5; envelope-from=iii@linux.ibm.com; helo=mx0b-001b2d01.pphosted.com X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, 2023-10-31 at 15:53 -0700, Richard Henderson wrote: > On 10/30/23 22:32, Ilya Leoshkevich wrote: > > +int main(void) > > +{ > > +=C2=A0=C2=A0=C2=A0 register unsigned long r0 asm("r0"); > > +=C2=A0=C2=A0=C2=A0 unsigned long mem =3D 42, rhs =3D 500; > > +=C2=A0=C2=A0=C2=A0 struct sigaction act; > > +=C2=A0=C2=A0=C2=A0 int err; > > + > > +=C2=A0=C2=A0=C2=A0 memset(&act, 0, sizeof(act)); > > +=C2=A0=C2=A0=C2=A0 act.sa_sigaction =3D handle_sigsegv; > > +=C2=A0=C2=A0=C2=A0 act.sa_flags =3D SA_SIGINFO; > > +=C2=A0=C2=A0=C2=A0 err =3D sigaction(SIGSEGV, &act, NULL); > > +=C2=A0=C2=A0=C2=A0 assert(err =3D=3D 0); > > + > > +=C2=A0=C2=A0=C2=A0 r0 =3D 100; > > +=C2=A0=C2=A0=C2=A0 asm("algr %[r0],%[rhs]\n" > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 "clc 0(8,%[mem]),0(0)\n"=C2= =A0 /* The 2nd operand will cause a > > SEGV. */ > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : [r0] "+r" (r0) > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : [mem] "r" (&mem) > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 , [rhs] "r" (rhs) > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 : "cc", "memory"); > > + >=20 > You could just as easily set cc based on CHI or something to avoid > hard-coding r0, or even=20 > clobbering an output register at all. The point of hardcoding r0 is rather to be able to check its value in handle_sigsegv(). While this was not buggy, I still wanted to make sure that the updated value is "committed" despite SEGV. >=20 > But I guess there's little point bike shedding this too much... >=20 > r~