Messages in this thread | | | Date | Tue, 20 Jun 2023 07:53:28 -0700 | Subject | Re: [PATCH bpf] bpf/btf: Accept function names that contain dots | From | Yonghong Song <> |
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On 6/20/23 7:38 AM, Nick Desaulniers wrote: > On Mon, Jun 19, 2023 at 2:17 PM Yonghong Song <yhs@meta.com> wrote: >> >> How many people really build the kernel with >> LLVM=1 LLVM_IAS=0 >> which uses clang compiler ans gcc 'as'. >> I think distro most likely won't do this if they intend to >> build the kernel with clang. >> >> Note that >> LLVM=1 >> implies to use both clang compiler and clang assembler. > > Yes, we prefer folks to build with LLVM=1. The problem exists for > users of stable kernels that predate LLVM_IAS=1 support working well > (4.19 is when we had most of the assembler related issues sorted out, > actually later but we backported most fixes to 4.19). > >> >> Using clang17 and 'LLVM=1 LLVM_IAS=0', with latest bpf-next, >> I actually hit some build errors like: >> >> /tmp/video-bios-59fa52.s: Assembler messages: >> /tmp/video-bios-59fa52.s:4: Error: junk at end of line, first >> unrecognized character is `"' > > Probably because: > 1. CONFIG_DEBUG_INFO_DWARF5=y was set or > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y and you're using a version > of clang which implicitly defaults to DWARFv5. > 2. you're using a version of GAS that does not understand DWARFv5. > 3. you did not run defconfig/menuconfig to have kconfig check for > DWARFv5 support.
Yes, I am using llvm17 which I think the default dwarf is v5, and indeed I have CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
My gas is 2.30, probably too old to support dwarf 5.
Yes, I didn't run defconfig/menuconfig.
> > The kconfigs should prevent you from selecting DWARFv5 if your > toolchain combination doesn't support it; if you run kconfig. > >> /tmp/video-bios-59fa52.s:4: Error: file number less than one >> /tmp/video-bios-59fa52.s:5: Error: junk at end of line, first >> unrecognized character is `"' >> /tmp/video-bios-59fa52.s:6: Error: junk at end of line, first >> unrecognized character is `"' >> /tmp/video-bios-59fa52.s:7: Error: junk at end of line, first >> unrecognized character is `"' >> /tmp/video-bios-59fa52.s:8: Error: junk at end of line, first >> unrecognized character is `"' >> /tmp/video-bios-59fa52.s:9: Error: junk at end of line, first >> unrecognized character is `"' >> /tmp/video-bios-59fa52.s:10: Error: junk at end of line, first >> unrecognized character is `"' >> /tmp/video-bios-59fa52.s:68: Error: junk at end of line, first >> unrecognized character is `"' >> clang: error: assembler command failed with exit code 1 (use -v to see >> invocation) >> make[4]: *** [/home/yhs/work/bpf-next/scripts/Makefile.build:252: >> arch/x86/realmode/rm/video-bios.o] Error 1 >> make[4]: *** Waiting for unfinished jobs.... >> /tmp/wakemain-88777c.s: Assembler messages: >> /tmp/wakemain-88777c.s:4: Error: junk at end of line, first unrecognized >> character is `"' >> /tmp/wakemain-88777c.s:4: Error: file number less than one >> /tmp/wakemain-88777c.s:5: Error: junk at end of line, first unrecognized >> character is `"' >> /tmp/wakemain-88777c.s:6: Error: junk at end of line, first unrecognized >> character is `"' >> /tmp/wakemain-88777c.s:7: Error: junk at end of line, first unrecognized >> character is `"' >> /tmp/wakemain-88777c.s:8: Error: junk at end of line, first unrecognized >> character is `"' >> /tmp/wakemain-88777c.s:81: Error: junk at end of line, first >> unrecognized character is `"' >> /tmp/wakemain-88777c.s:312: Error: junk at end of line, first >> unrecognized character is `"' >> clang: error: assembler command failed with exit code 1 (use -v to see >> invocation) >> >> Potentially because of my local gnu assembler 2.30-120.el8 won't work > > It's recorded in lib/Kconfig.debug that 2.35.2 is required for DWARFv5 > support if you're using GAS. My machine has 2.40. > >> with some syntax generated by clang. Mixing clang compiler and arbitrary >> gnu assembler are not a good idea (see the above example). It might > > I agree, but for older branches of stable which are still supported, > we didn't quite have clang assembler support usable. We still need to > support those branches of stable.
Thanks Florent pointing out 5.10 stable kernels which have this issue. I am okay with backporting to old stable kernels if that is needed. But the patch going to bpf-next should not have a bug-fix tag and the patch commit message can be tweaked for backport to 5.10 though.
> >> work with close-to-latest gnu assembler. >> >> To support function name like '<fname>.isra', some llvm work will be >> needed, and it may take some time. >> >> So in my opinion, this patch is NOT a bug fix. It won't affect distro. >> Whether we should backport to the old kernel, I am not sure whether it >> is absolutely necessary as casual build can always remove LLVM_IAS=0 or >> hack the kernel source itself. > > >
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