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Marchesi" , Beau Belgrave , Linus Torvalds , Andrew Morton , Jens Axboe , Florian Weimer , Sam James Subject: Re: [RFC PATCH v1 11/16] s390/unwind_user/sframe: Enable HAVE_UNWIND_USER_SFRAME Message-ID: <20250801125350.9905B20-hca@linux.ibm.com> References: <20250710163522.3195293-1-jremus@linux.ibm.com> <20250710163522.3195293-12-jremus@linux.ibm.com> Precedence: bulk X-Mailing-List: bpf@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: <20250710163522.3195293-12-jremus@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: BAGEYFyOjhcKCT6uRHhsnl48vgulLEex X-Proofpoint-GUID: BAGEYFyOjhcKCT6uRHhsnl48vgulLEex X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODAxMDA5MiBTYWx0ZWRfX2prHMf8SZzOt dFahisWf+YI1ynsFhUwkRqOkgc0PbQ+8TgjAVcymyypToUVqaA9NFlLYJRgjH0aKjM8eDwtEFoi rz+nuCkolnJQs3yg5skvKJbUt8GU3ZN9D41rED2Hl1fWaPLmnGPHw1eNB/eU5mlZ1uy8GlEQl+/ VgaHrFjdDE2C3SHAO8H2/ziyY88HC9wooRuRaWDInrGlyrykymJnvijtW0c5oMKlAChOLwibhGF WjPGoSlK4/xdgrWUkajj26ugTxVrMVCrJ+3Z2twKyj2K6MtmkurlbohSIy8RF6VDL+FShqtK/QC GlmbUXugnIDn3Z+CAXZePneKlX8UZiNlwyA9vhXjt07ac4VwJWgTqYOY2astV6vOH0sMk8lFfyM FsP/xh2QUe1D7Jot0IxSds6ZFJk2qv6bcNZSlbeDpXqjj+RXmYjmiTwWPfg2Y4CXmObTzyx+ X-Authority-Analysis: v=2.4 cv=ZoDtK87G c=1 sm=1 tr=0 ts=688cb8e5 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=kj9zAlcOel0A:10 a=2OwXVqhp2XgA:10 a=vXNe0y40mXAc93P3-MgA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-08-01_04,2025-07-31_03,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 priorityscore=1501 lowpriorityscore=0 mlxscore=0 clxscore=1015 adultscore=0 impostorscore=0 mlxlogscore=439 bulkscore=0 phishscore=0 suspectscore=0 malwarescore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505280000 definitions=main-2508010092 On Thu, Jul 10, 2025 at 06:35:17PM +0200, Jens Remus wrote: > Add s390 support for unwinding of user space using SFrame. This > leverages the previous commits to address the following s390 > particularities: > > - The CFA is defined as the value of the stack pointer (SP) at call > site in the previous frame + 160. Therefore the SP unwinds as > SP = CFA - 160. Therefore use a SP value offset from CFA of -160. > > - The return address (RA) is not saved on the stack at function entry. > It is also not saved in the function prologue, when in leaf functions. > Therefore the RA does not necessarily need to be unwound in the first > unwinding step for the topmost frame. > > - The frame pointer (FP) and/or return address (RA) may be saved in > other registers when in leaf functions. GCC effectively uses > floating-point registers (FPR) for this purpose. Therefore DWARF > register numbers may be encoded in the SFrame FP/RA offsets. ... > +static inline void __s390_get_dwarf_fpr(unsigned long *val, int regnum) > +{ > + switch (regnum) { > + case 16: > + fpu_std(0, (freg_t *)val); > + break; ... > +static inline int s390_unwind_user_get_reg(unsigned long *val, int regnum) > +{ > + if (0 <= regnum && regnum <= 15) { > + struct pt_regs *regs = task_pt_regs(current); > + *val = regs->gprs[regnum]; > + } else if (16 <= regnum && regnum <= 31) { > + __s390_get_dwarf_fpr(val, regnum); This won't work with other potential in-kernel fpu users. User space fpr contents may have been written to the current task's fpu save area and fprs may have been clobbered by in-kernel users; so you need to get register contents from the correct location. See arch/s390/include/asm/fpu.h.