On Tue, Jun 11, 2024 at 03:07:29PM +0200, Mark Wielaard wrote: > Hi, > > Adding elfutils-devel to CC to keep everyone up to date on the state of > the patches. > > On Mon, 2024-06-10 at 23:36 -0700, Tony Ambardar wrote: > > On Mon, Jun 03, 2024 at 08:47:24PM -0700, Tony Ambardar wrote: > > > On Mon, Jun 03, 2024 at 09:18:33PM +0200, Mark Wielaard wrote: > > > > On Mon, Jun 03, 2024 at 02:40:45PM -0300, Arnaldo Carvalho de Melo wrote: > > > > > Couldn't find a way to ask eu-readelf for more verbose output, where we > > > > > could perhaps get some clue as to why it produces nothing while binutils > > > > > readelf manages to grok it, Mark, do you know some other way to ask > > > > > eu-readelf to produce more debug output? > > > > > > > > > > I'm unsure if the netdevsim.ko file was left in a semi encoded BTF state > > > > > that then made eu-readelf to not be able to process it while pahole, > > > > > that uses eltuils' libraries, was able to process the first two CUs for > > > > > a kernel module and all the CUs for the vmlinux file :-\ > > > > > > > > > > Mark, the whole thread is available at: > > > > > > > > > > https://lore.kernel.org/all/Zl3Zp5r9m6X_i_J4@x1/T/#u > > > > > > > > I haven't looked at the vmlinux file. But for the .ko file the issue > > > > is that the elfutils MIPS backend isn't complete. Specifically MIPS > > > > relocations aren't recognized (and so cannot be applied). There are > > > > some pending patches which try to fix that: > > > > > > > > https://patchwork.sourceware.org/project/elfutils/list/?series=31601 > > > > > > Earlier in the thread, Hengqi Chen pointed out the latest elfutils backend > > > work for MIPS, and I locally rebuilt elfutils and then pahole from their > > > respective next/main branches. For elfutils, main (935ee131cf7c) includes > > > > > > e259f126 Support Mips architecture > > > f2acb069 stack: Fix stack unwind failure on mips > > > db33cb0c backends: Add register_info, return_value_location, core_note mips > > > > > > which partially applies the patchwork series but leaves out the support for > > > readelf, strip, and elflint. > > > > > > I believe this means the vmlinux and .ko files I shared are OK, or is there > > > more backend work needed for MIPS? > > > > > > The bits missing in eu-readelf would explain the blank output both Arnaldo > > > and I see from "$ eu-readelf -winfo vmlinux". I tried rebuilding with the > > > patchwork readelf patch locally but ran into merge conflicts. > > > > A short update, starting with answering my own question. > > > > No, apparently the above commits *do not* complete the backend work. Ying > > Huang submitted additional related patches since March 5: [1][2] > > > > strip: Adapt src/strip -o -f on mips > > readelf: Adapt src/readelf -h/-S/-r/-w/-l/-d/-a on mips > > elflint: adapt src/elflint --gnu src/nm on mips > > test: Add mips in run-allregs.sh and run-readelf-mixed-corenote.sh > > > > Despite the titles, these patches do include core backend changes for MIPS. > > I resolved the various merge conflicts [3], rebuilt elfutils, and retested > > kernel builds to now find: > > > > - pahole is able to read DWARF[45] info and create .BTF for modules > > - resolve_btfids can successfully patch .BTF_ids in modules > > - kernel successfully loads modules with BTF and kfuncs (tested 6.6 LTS) > > > > Huzzah! > > > > > > Ying: > > > > Thank you for developing these MIPS patches. In your view, are the MIPS > > changes now complete, or do you plan further updates that might improve or > > impact parsing DWARF debug/reloc info in apps like pahole? > > > > > > Mark: > > > > Given that BTF usage on Linux/MIPS is basically broken without these > > patches, could I request some of your review time for them to be merged? If > > it's helpful, my branch [3] includes all patches with conflicts fixed, and > > I also successfully ran the elfutils self-tests (including MIPS from Ying). > > Please feel free to add for these patches: > > > > Tested-by: Tony Ambardar <Tony.Ambardar@xxxxxxxxx> > > Yes, I would very much like to integrate the rest of these patches. But > I keep running out of time. The main issues were that, as you noticed, > the patches mix backend and frontend tool changes a bit. I don't have > access to a MIPS system to test them on. There are a couple of > different MIPS abis (I believe all combinations of 32/64 bit and > big/little endianness), but people have only tested on mips64le (maybe > that is the only relevant one these days?) And finally the way MIPS > represents relocations is slightly different than any other ELF > architecture does. So we have to translate that somewhere to make the > standards functions work. I have to convince myself that doing that in > elf_getdata as the patches do is the right place. > Glad to hear there's strong interest. Not much I can add to the code structure discussion but I *can* confirm my testing included both mips64el and mips32be, specifically to improve word-size/endianness coverage. The former is supported by Debian, while the latter can still be found on many embedded devices like consumer routers. If you need additional testing for review/merge I can help with that (using OpenWrt/QEMU primarily). > > Many thanks everyone for your help, > > Tony > > > > [1]: https://patchwork.sourceware.org/project/elfutils/list/?series=31601 > > [2]: https://patchwork.sourceware.org/project/elfutils/list/?series=34310 > > [3]: > > https://github.com/guidosarducci/elfutils/commits/main-fix-mips-support-reloc/ >
