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Tue, 26 May 2026 13:17:20 +0000 (GMT) Received: from osiris (unknown [9.52.214.206]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTPS; Tue, 26 May 2026 13:17:20 +0000 (GMT) Date: Tue, 26 May 2026 15:17:18 +0200 From: Heiko Carstens To: Marco Elver Cc: Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com Subject: Re: [PATCH] s390: Implement _THIS_IP_ using inline asm Message-ID: <20260526131718.9778B73-hca@linux.ibm.com> References: <20260521122727.142280-1-elver@google.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=us-ascii Content-Disposition: inline In-Reply-To: <20260521122727.142280-1-elver@google.com> X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=OdqoyBTY c=1 sm=1 tr=0 ts=6a159d65 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=kj9zAlcOel0A:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=mDV3o1hIAAAA:8 a=NEAV23lmAAAA:8 a=1XWaLZrsAAAA:8 a=VnNF1IyMAAAA:8 a=kDix7j7DZTOcE0wP3AwA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-GUID: fNHlpc8Dtb3xBM2K8RfIIRb1RuwkNAyg X-Proofpoint-ORIG-GUID: m3PnYVOt16oPwZ8UZB8iqH8Tf6ZlAWfN X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTI2MDExMyBTYWx0ZWRfX3F0xLZBxIGSq Fb1iNRqRPpo82hicXP1+srJwI7qOZOK+BYy66cC0CqQCAIH9jRny8P2VyerahCD4HRlzwXX65XG QDTjLnndRPR4qFaZS7xmyrvwVSUV0EbSJxC3G+fDmFvNOPLIXaXIzDYnQNVrrfRgcYLrOZhKJSn v416EDdHfjZsxAzY5vQxZ3eGvB2nAybTLe9TXg1FcZowbP++cgHcitwe9lIZ4+B5ncs6vc1XqZ8 PNHbtMf8ZNOfZUz2ULk1c13DQMd3yf1WFq7t5CcWcSK/CL6xfNE82IcBRa8mdqWUkw25EFAEOZB p68Lvyi6SyVLurFtwlEpBdRntiVzLBQ6O8EUgRh2NSWEGxavcbH5x6XiX7zDn4D0yxKpETovm6y q/+VmdCFlB72gLw2ohundn0ZT/T82LYwAZVn8ayLgp/4V0ogQks3KHNPMTy5+iLFufbmnqxHNTv BxsuJdXyqTUE4a1NTuA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-05-26_03,2026-05-26_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 impostorscore=0 clxscore=1015 malwarescore=0 lowpriorityscore=0 bulkscore=0 suspectscore=0 adultscore=0 spamscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605130000 definitions=main-2605260113 On Thu, May 21, 2026 at 02:27:23PM +0200, Marco Elver wrote: > Both GCC [1] and Clang [2] consider the generic version of _THIS_IP_ to > be broken: > > #define _THIS_IP_ ({ __label__ __here; __here: (unsigned long)&&__here; }) > > In particular, the address of a label is only expected to be used with a > computed goto. > > While the generic version more or less works today, it is known to be > brittle and may break with current and future optimizations. For > example, Clang -O2 always returns 1 when this function is inlined: > > static inline unsigned long get_ip(void) > { return ({ __label__ __here; __here: (unsigned long)&&__here; }); } > > Fix it by overriding _THIS_IP_ in (which is included by > ) using an architecture-specific inline asm > version. Additionally, avoiding taking the address of a label prevents > compilers from emitting spurious indirect branch targets (e.g. ENDBR or > BTI) under control-flow integrity schemes. > > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120071 [1] > Link: https://github.com/llvm/llvm-project/issues/138272 [2] > Signed-off-by: Marco Elver > --- > arch/s390/include/asm/linkage.h | 2 ++ > 1 file changed, 2 insertions(+) Reviewed-by: Heiko Carstens