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linux-kernel@vger.kernel.org On 4/13/23 9:30 AM, Josh Poimboeuf wrote: > On Thu, Apr 13, 2023 at 09:59:31AM -0500, Madhavan T. Venkataraman wrote: >> On 4/12/23 10:52, Josh Poimboeuf wrote: >>> On Wed, Apr 12, 2023 at 09:50:23AM -0500, Madhavan T. Venkataraman wrote: >>>>>> I read through the SFrame spec file briefly. It looks like I can easily adapt my >>>>>> version 1 of the livepatch patchset which was based on DWARF to SFrame. If the compiler >>>>>> folks agree to properly support and maintain SFrame, then I could send the next version >>>>>> of the patchset based on SFrame. >>>>>> >>>>>> But I kinda need a clear path forward before I implement anything. I request the arm64 >>>>>> folks to comment on the above approach. Would it be useful to initiate an email discussion >>>>>> with the compiler folks on what they plan to do to support SFrame? Or, should this all >>>>>> happen face to face in some forum like LPC? >>>>> >>>>> SFrame is basically a simplified version of DWARF unwind, using it as an >>>>> input to objtool is going to have the same issues I mentioned below (and >>>>> as was discussed with your v1). >>>>> >>>> >>>> Yes. It is a much simplified version of DWARF. So, I am hoping that the compiler folks >>>> can provide the feature with a reliability guarantee. DWARF is too complex. >>> >>> I don't see what the complexity (or lack thereof) of the unwinding data >>> format has to do with it. The unreliability comes from the underlying >>> data source, not the formatting of the data. >>> >> >> What I meant is - if SFrame is implemented by simply extracting unwind info from >> DWARF data and placing it in a separate section (as it is probably implemented now), >> then what you say is totally true. But if the compiler folks agree to make SFrame reliable, >> then either they have to make DWARF reliable. Or, they have to implement SFrame as a >> separate feature and make it reliable. The former is tough to do as DWARF has a lot of complexity. >> The latter is a lot easier to do. SFrame stack trace data is generated by the GNU assembler, by using the .cfi_* asm directives embedded by the compiler. So, it is true that the source of EH_Frame info and SFrame stack trace data is the same. That said, yes, if you see bugs/inconsistencies in SFrame/EH_Frame info, please file the issue(s). > > [ adding linux-toolchains ] > > I don't think ensuring reliability is an easy task, regardless of the > complexity of the unwinding format. > > Whether it's SFrame or DWARF/eh_frame, the question would be how to > ensure it's always reliable for a compiler "power user" like the kernel > which has many edge cases (including lots of inline asm which the > compiler has no visibility to) and which uses unwinding for more than > just debugging. > > It would need some kind of black-box testing on a complex code base. > (hint: kind of like what objtool already does today) >