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X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 6eXcWE1utq3fE4Wf55Ll+5rNGJKZWRDLGv+hBzZ8z7f73M9VAEHiqI4J3el7YRhSXPXIVrMgXqbldY9AAW2R2Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BLAPR10MB5188 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-02-28_01,2025-02-27_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 mlxlogscore=999 suspectscore=0 adultscore=0 phishscore=0 bulkscore=0 malwarescore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2502100000 definitions=main-2502280046 X-Proofpoint-ORIG-GUID: TmIMBhPhzbG8sCuvlGYrgwDrR3Y6qeTJ X-Proofpoint-GUID: TmIMBhPhzbG8sCuvlGYrgwDrR3Y6qeTJ On 2/27/25 1:38 AM, Puranjay Mohan wrote: > Indu Bhagat writes: > >> On 2/26/25 2:23 AM, Puranjay Mohan wrote: >>> Indu Bhagat writes: >>> >>>> On 2/25/25 3:54 PM, Weinan Liu wrote: >>>>> On Tue, Feb 25, 2025 at 11:38 AM Indu Bhagat wrote: >>>>>> >>>>>> On Mon, Feb 10, 2025 at 12:30 AM Weinan Liu wrote: >>>>>>>> I already have a WIP patch to add sframe support to the kernel module. >>>>>>>> However, it is not yet working. I had trouble unwinding frames for the >>>>>>>> kernel module using the current algorithm. >>>>>>>> >>>>>>>> Indu has likely identified the issue and will be addressing it from the >>>>>>>> toolchain side. >>>>>>>> >>>>>>>> https://sourceware.org/bugzilla/show_bug.cgi?id=32666 >>>>>>> >>>>>>> I have a working in progress patch that adds sframe support for kernel >>>>>>> module. >>>>>>> https://github.com/heuza/linux/tree/sframe_unwinder.rfc >>>>>>> >>>>>>> According to the sframe table values I got during runtime testing, looks >>>>>>> like the offsets are not correct . >>>>>>> >>>>>> >>>>>> I hope to sanitize the fix for 32666 and post upstream soon (I had to >>>>>> address other related issues).  Unless fixed, relocating .sframe >>>>>> sections using the .rela.sframe is expected to generate incorrect output. >>>>>> >>>>>>> When unwind symbols init_module(0xffff80007b155048) from the kernel >>>>>>> module(livepatch-sample.ko), the start_address of the FDE entries in the >>>>>>> sframe table of the kernel modules appear incorrect. >>>>>> >>>>>> init_module will apply the relocations on the .sframe section, isnt it ? >>>>>> >>>>>>> For instance, the first FDE's start_addr is reported as -20564. Adding >>>>>>> this offset to the module's sframe section address (0xffff80007b15a040) >>>>>>> yields 0xffff80007b154fec, which is not within the livepatch-sample.ko >>>>>>> memory region(It should be larger than 0xffff80007b155000). >>>>>>> >>>>>> >>>>>> Hmm..something seems off here.  Having tested a potential fix for 32666 >>>>>> locally, I do not expect the first FDE to show this symptom. >>>>>> >>>>> >>> >>> Hi, >>> >>> Sorry for not responding in the past few days. I was on PTO and was >>> trying to improve my snowboarding technique, I am back now!! >>> >>> I think what we are seeing is expected behaviour: >>> >>> | For instance, the first FDE's start_addr is reported as -20564. Adding >>> | this offset to the module's sframe section address (0xffff80007b15a040) >>> | yields 0xffff80007b154fec, which is not within the livepatch-sample.ko >>> | memory region(It should be larger than 0xffff80007b155000). >>> >>> >>> Let me explain using a __dummy__ example. >>> >>> Assume Memory layout before relocation: >>> >>> | Address | Element | Relocation >>> | .... | .... | >>> | 60 | init_module (start address) | >>> | 72 | init_module (end address) | >>> | .... | ..... | >>> | 100 | Sframe section header start address | >>> | 128 | First FDE's start address | RELOC_OP_PREL -> Put init_module address (60) - current address (128) >>> >>> So, after relocation First FDE's start address has value 60 - 128 = -68 >>> >> >> For SFrame FDE function start address is : >> >> "Signed 32-bit integral field denoting the virtual memory address of the >> described function, for which the SFrame FDE applies. The value encoded >> in the ‘sfde_func_start_address’ field is the offset in bytes of the >> function’s start address, from the SFrame section." >> >> So, in your case, after applying the relocations, you will get: >> S + A - P = 60 - 128 = -68 >> >> This is the distance of the function start address (60) from the current >> location in SFrame section (128) >> >> But what we intend to store is the distance of the function start >> address from the start of the SFrame section. So we need to do an >> additional step for SFrame FDE: Value += r_offset > > Thanks for the explaination, now it makes sense. > > But I couldn't find a relocation type in AARCH64 that does this extra += > r_offset along with PREL32. > > The kernel's module loader is only doing the R_AARCH64_PREL32 which is > why we see this issue. > > How is this working even for the kernel itself? or for that matter, any > other binary compiled with sframe? > For the usual executables or shared objects, the calculations are applied by ld.bfd at this time. Hence, the issue manifests in relocatable files. > From my limited undestanding, the way to fix this would be to hack the > relocator to do this additional step while relocating .sframe sections. > Or the 'addend' values in .rela.sframe should already have the +r_offset > added to it, then no change to the relocator would be needed. > Of the two, adjusting the addend values in .rela.sframe may be a reasonable way to go about it. Let me try it out in GAS and ld.bfd. >> -68 + 28 = -40 >> Where 28 is the r_offset in the RELA. >> >> So we really expect a -40 in the relocated SFrame section instead of -68 >> above. IOW, the RELAs of SFrame section will need an additional step >> after relocation. >> > > Thanks, > Puranjay