> On Jan 17, 2023, at 3:30 PM, Christophe Leroy <christophe.leroy@xxxxxxxxxx> wrote: > > > > Le 17/01/2023 à 06:30, Tonghao Zhang a écrit : >> >> >>> On Jan 9, 2023, at 4:15 PM, Christophe Leroy <christophe.leroy@xxxxxxxxxx> wrote: >>> >>> >>> >>> Le 06/01/2023 à 16:37, Daniel Borkmann a écrit : >>>> On 1/5/23 6:53 PM, Christophe Leroy wrote: >>>>> Le 05/01/2023 à 04:06, tong@xxxxxxxxxxxxx a écrit : >>>>>> From: Tonghao Zhang <tong@xxxxxxxxxxxxx> >>>>>> >>>>>> The x86_64 can't dump the valid insn in this way. A test BPF prog >>>>>> which include subprog: >>>>>> >>>>>> $ llvm-objdump -d subprog.o >>>>>> Disassembly of section .text: >>>>>> 0000000000000000 <subprog>: >>>>>> 0: 18 01 00 00 73 75 62 70 00 00 00 00 72 6f 67 00 r1 >>>>>> = 29114459903653235 ll >>>>>> 2: 7b 1a f8 ff 00 00 00 00 *(u64 *)(r10 - 8) = r1 >>>>>> 3: bf a1 00 00 00 00 00 00 r1 = r10 >>>>>> 4: 07 01 00 00 f8 ff ff ff r1 += -8 >>>>>> 5: b7 02 00 00 08 00 00 00 r2 = 8 >>>>>> 6: 85 00 00 00 06 00 00 00 call 6 >>>>>> 7: 95 00 00 00 00 00 00 00 exit >>>>>> Disassembly of section raw_tp/sys_enter: >>>>>> 0000000000000000 <entry>: >>>>>> 0: 85 10 00 00 ff ff ff ff call -1 >>>>>> 1: b7 00 00 00 00 00 00 00 r0 = 0 >>>>>> 2: 95 00 00 00 00 00 00 00 exit >>>>>> >>>>>> kernel print message: >>>>>> [ 580.775387] flen=8 proglen=51 pass=3 image=ffffffffa000c20c >>>>>> from=kprobe-load pid=1643 >>>>>> [ 580.777236] JIT code: 00000000: cc cc cc cc cc cc cc cc cc cc cc >>>>>> cc cc cc cc cc >>>>>> [ 580.779037] JIT code: 00000010: cc cc cc cc cc cc cc cc cc cc cc >>>>>> cc cc cc cc cc >>>>>> [ 580.780767] JIT code: 00000020: cc cc cc cc cc cc cc cc cc cc cc >>>>>> cc cc cc cc cc >>>>>> [ 580.782568] JIT code: 00000030: cc cc cc >>>>>> >>>>>> $ bpf_jit_disasm >>>>>> 51 bytes emitted from JIT compiler (pass:3, flen:8) >>>>>> ffffffffa000c20c + <x>: >>>>>> 0: int3 >>>>>> 1: int3 >>>>>> 2: int3 >>>>>> 3: int3 >>>>>> 4: int3 >>>>>> 5: int3 >>>>>> ... >>>>>> >>>>>> Until bpf_jit_binary_pack_finalize is invoked, we copy rw_header to >>>>>> header >>>>>> and then image/insn is valid. BTW, we can use the "bpftool prog dump" >>>>>> JITed instructions. >>>>> >>>>> NACK. >>>>> >>>>> Because the feature is buggy on x86_64, you remove it for all >>>>> architectures ? >>>>> >>>>> On powerpc bpf_jit_enable == 2 works and is very usefull. >>>>> >>>>> Last time I tried to use bpftool on powerpc/32 it didn't work. I don't >>>>> remember the details, I think it was an issue with endianess. Maybe it >>>>> is fixed now, but it needs to be verified. >>>>> >>>>> So please, before removing a working and usefull feature, make sure >>>>> there is an alternative available to it for all architectures in all >>>>> configurations. >>>>> >>>>> Also, I don't think bpftool is usable to dump kernel BPF selftests. >>>>> That's vital when a selftest fails if you want to have a chance to >>>>> understand why it fails. >>>> >>>> If this is actively used by JIT developers and considered useful, I'd be >>>> ok to leave it for the time being. Overall goal is to reach feature parity >>>> among (at least major arch) JITs and not just have most functionality only >>>> available on x86-64 JIT. Could you however check what is not working with >>>> bpftool on powerpc/32? Perhaps it's not too much effort to just fix it, >>>> but details would be useful otherwise 'it didn't work' is too fuzzy. >>> >>> Sure I will try to test bpftool again in the coming days. >>> >>> Previous discussion about that subject is here: >>> https://patchwork.kernel.org/project/linux-riscv/patch/20210415093250.3391257-1-Jianlin.Lv@xxxxxxx/#24176847= >> Hi Christophe >> Any progress? We discuss to deprecate the bpf_jit_enable == 2 in 2021, but bpftool can not run on powerpc. >> Now can we fix this issue? > > Hi Tong, > > I have started to look at it but I don't have any fruitfull feedback yet. > > In the meantime, were you able to confirm that bpftool can also be used > to dump jitted tests from test_bpf.ko module on x86_64 ? In that can you > tell me how to proceed ? Now I do not test, but we can dump the insn after bpf_prog_select_runtime in test_bpf.ko. bpf_map_get_info_by_fd can copy the insn to userspace, but we can dump them in test_bpf.ko in the same way. > Thanks > Christophe > >>> >>>> >>>> Also, with regards to the last statement that bpftool is not usable to >>>> dump kernel BPF selftests. Could you elaborate some more? I haven't used >>>> bpf_jit_enable == 2 in a long time and for debugging always relied on >>>> bpftool to dump xlated insns or JIT. Or do you mean by BPF selftests >>>> the test_bpf.ko module? Given it has a big batch with kernel-only tests, >>>> there I can see it's probably still useful. >>> >>> Yes I mean test_bpf.ko >>> >>> I used it as the test basis when I implemented eBPF for powerpc/32. And >>> not so long ago it helped decover and fix a bug, see >>> https://github.com/torvalds/linux/commit/89d21e259a94f7d5582ec675aa445f5a79f347e4 >>> >>>> >>>> Cheers, >>>> Daniel
