Christophe Leroy wrote: > > > Le 20/04/2021 à 05:28, Alexei Starovoitov a écrit : > > On Sat, Apr 17, 2021 at 1:16 AM Christophe Leroy > > <christophe.leroy@xxxxxxxxxx> wrote: > >> > >> > >> > >> Le 16/04/2021 à 01:49, Alexei Starovoitov a écrit : > >>> On Thu, Apr 15, 2021 at 8:41 AM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote: > >>>> > >>>> 2021-04-15 16:37 UTC+0200 ~ Daniel Borkmann <daniel@xxxxxxxxxxxxx> > >>>>> On 4/15/21 11:32 AM, Jianlin Lv wrote: > >>>>>> For debugging JITs, dumping the JITed image to kernel log is discouraged, > >>>>>> "bpftool prog dump jited" is much better way to examine JITed dumps. > >>>>>> This patch get rid of the code related to bpf_jit_enable=2 mode and > >>>>>> update the proc handler of bpf_jit_enable, also added auxiliary > >>>>>> information to explain how to use bpf_jit_disasm tool after this change. > >>>>>> > >>>>>> Signed-off-by: Jianlin Lv <Jianlin.Lv@xxxxxxx> > >>>> > >>>> Hello, > >>>> > >>>> For what it's worth, I have already seen people dump the JIT image in > >>>> kernel logs in Qemu VMs running with just a busybox, not for kernel > >>>> development, but in a context where buiding/using bpftool was not > >>>> possible. > >>> > >>> If building/using bpftool is not possible then majority of selftests won't > >>> be exercised. I don't think such environment is suitable for any kind > >>> of bpf development. Much so for JIT debugging. > >>> While bpf_jit_enable=2 is nothing but the debugging tool for JIT developers. > >>> I'd rather nuke that code instead of carrying it from kernel to kernel. > >>> > >> > >> When I implemented JIT for PPC32, it was extremely helpfull. > >> > >> As far as I understand, for the time being bpftool is not usable in my environment because it > >> doesn't support cross compilation when the target's endianess differs from the building host > >> endianess, see discussion at > >> https://lore.kernel.org/bpf/21e66a09-514f-f426-b9e2-13baab0b938b@xxxxxxxxxx/ > >> > >> That's right that selftests can't be exercised because they don't build. > >> > >> The question might be candid as I didn't investigate much about the replacement of "bpf_jit_enable=2 > >> debugging mode" by bpftool, how do we use bpftool exactly for that ? Especially when using the BPF > >> test module ? > > > > the kernel developers can add any amount of printk and dumps to debug > > their code, > > but such debugging aid should not be part of the production kernel. > > That sysctl was two things at once: debugging tool for kernel devs and > > introspection for users. > > bpftool jit dump solves the 2nd part. It provides JIT introspection to users. > > Debugging of the kernel can be done with any amount of auxiliary code > > including calling print_hex_dump() during jiting. > > > > I get the following message when trying the command suggested in the patch message: > > root@vgoip:~# ./bpftool prog dump jited > Error: No libbfd support > > Christophe Seems your bpftool prog was built without libbfd, can you rebuild with libbfd installed. .John
