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Peter Anvin" , Jonathan Corbet , Shuah Khan , Huacai Chen , WANG Xuerui , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Andy Lutomirski , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Andrew Donnellan , Mark Rutland , Arnd Bergmann , Jiaxun Yang , Ryan Roberts , Greg Kroah-Hartman , Mukesh Kumar Chaurasiya , Shrikanth Hegde , Zong Li , Nam Cao , Deepak Gupta , Lukas Gerlach , Rui Qi , Kees Cook , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org Subject: Re: [RFC] entry: Untangle the return value of syscall_enter_from_user_mode from syscall NR In-Reply-To: References: <87h5mhnjsr.ffs@fw13> <87ldbsmnie.ffs@fw13> <20260703105718.GO751831@noisy.programming.kicks-ass.net> Date: Fri, 03 Jul 2026 13:39:18 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzAzMDExMCBTYWx0ZWRfX9A1mR90iQ9fU Jnq5F39WZRpZmJZJo+YsMXBKsZBl5gTM0jj9mCML5R/Bd24LYkLFgakI/FJBKEk/4h15P+huPhT Qt4x0X5evHrib3jUNImZ7xP5zALzpi3mdHxCzHrZiWHfDxHBlxixkSy9cDZPp/nTWVn344jkMMG O12i1eIjoY94y3kSaaPRuWeqICdkdOzFC9qN9cXcDbd4yx6KKWE4d1phTqPs9FLJ4FlkNJ8+4fa /LYyk6rTIsgzLZV9WgaObJlQoHbWw7lz4c+lbe8M9Y7kkveYms1BJh6DmtlzccJMJ25zlPyUfZ8 JmMUjXhd8ewPBbHid4BGyyAMEeqTyK6ykKlCepPfXv4InKeRsqJriegDf9oxa/3VabPxqAi+ZDP fSV0sApuWT7vTMVqvinurA0q0Phf9Nlh1Md0MKTtLGwkyMUTXh+Ps6RpfCKXyu2yzYMrNM67vWx yRdPu407r0ZBuNDOK9g== X-Proofpoint-GUID: 0UewXK-tXcTk8FWkyPWn8VMN9H9juXe0 X-Authority-Analysis: v=2.4 cv=Z8bc2nRA c=1 sm=1 tr=0 ts=6a479f6c cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=7COA2AqOHvKb0wdBt1EA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzAzMDExMCBTYWx0ZWRfX+Zctx0ZJQz6V Vq7aSPRPQpmK2s8ZW9Ab8ojRDqpVU5I5jpBSa8I4jJz5wtRMPZX84BaKOeHe7JCg0Z84TaNiznM cYzIAWu4Lm8wE8gWWhsc6/49iUcKYqo= X-Proofpoint-ORIG-GUID: XUA9fyTmm3_KCsdJOv0Gf6JjV0mivGPV 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=2026-07-03_02,2026-06-26_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 adultscore=0 spamscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 phishscore=0 bulkscore=0 lowpriorityscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607030110 Michal Such=C3=A1nek writes: > The same could be asked of syscall_enter_from_user_mode. I find it very > odd. Why does it conflate the syscall number with its return value? > > It never uses the syscall number passed in except when returning it > unchanged. When it pokes the registers it reads the syscall number from > them. > > If the caller of syscall_enter_from_user_mode only read the syscall > number from the registers when syscall_enter_from_user_mode returns and > indicates the syscall should be still executed this whole shenigan would I agree. The fact that if (nr < NR_syscall) just works because -1 gets casted to 0xffffffff and is therefore out of bounds is very odd.