On Mon, Mar 8, 2021 at 5:02 AM Arnaldo Carvalho de Melo <arnaldo.melo@xxxxxxxxx> wrote: > > Em Mon, Mar 08, 2021 at 04:02:58AM +0100, Ilya Leoshkevich escreveu: > > On Sun, 2021-03-07 at 11:09 -0300, Arnaldo Carvalho de Melo wrote: > > > Adding Jiri to the CC list. > > > Em Sun, Mar 07, 2021 at 10:50:19AM -0300, Arnaldo Carvalho de Melo escreveu: > > > > Em Sun, Mar 07, 2021 at 10:44:21AM -0300, Arnaldo Carvalho de Melo escreveu: > > > > Now will build a kernel with this new version, reboot, then push > > > > publicly. > > > > So now trying to build v5.12-rc2 with pahole supporting BTF_KIND_FLOAT: > > > > AS .tmp_vmlinux.kallsyms2.S > > > LD vmlinux > > > BTFIDS vmlinux > > > FAILED: load BTF from vmlinux: Invalid argument > > > make[1]: *** [/home/acme/git/linux/Makefile:1197: vmlinux] Error 255 > > > make[1]: Leaving directory '/home/acme/git/build/v5.12.0-rc2' > > > make: *** [Makefile:215: __sub-make] Error 2 > > > [acme@five linux]$ > > > > [acme@five linux]$ egrep BTF\|DWARF ../build/v5.12.0-rc2/.config > > > CONFIG_VIDEO_SONY_BTF_MPX=m > > > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y > > > # CONFIG_DEBUG_INFO_DWARF4 is not set > > > CONFIG_DEBUG_INFO_BTF=y > > > CONFIG_PAHOLE_HAS_SPLIT_BTF=y > > > CONFIG_DEBUG_INFO_BTF_MODULES=y > > > > Ideas? > > > So v5.12-rc2 does not have this series yet: > > > https://lore.kernel.org/bpf/20210226202256.116518-1-iii@xxxxxxxxxxxxx/ > > > pahole generates a BTF_KIND_FLOAT, but libbpf from v5.12-rc2 doesn't > > know how to handle it and resolve_btfids fails. > > > I guess this is the first time a new BTF kind is added? I checked the > > history, and kernel v5.2, which introduced DEBUG_INFO_BTF, already had > > BTF_KIND_DATASEC. > > > So should I add a command-line option to pahole, which would tell it > > the desired libbpf compatibility level? > > Yes, that would be best, some sort of capability querying and then a > decision about using the new feature. pahole could be used to add .BTF post-factum to vmlinux image of a very old kernel, even the one that doesn't support BTF at all. So whatever detection system is going to be added, we should make it easy to turn it off. > > - Arnaldo
