Re: [bpf-next v2] bpf: drop deprecated bpf_jit_enable == 2

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> On Jan 17, 2023, at 11:59 PM, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
> 
> On 1/17/23 3:22 PM, Tonghao Zhang wrote:
>>> 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.
> 
> Issue is that these progs are not consumable from userspace (and therefore not bpftool).
> it's just simple bpf_prog_alloc + copy of test insns + bpf_prog_select_runtime() to test
> JITs (see generate_filter()). Some of them could be converted over to test_verifier, but
> not all might actually pass verifier, iirc. Don't think it's a good idea to allow exposing
> them via fd tbh.
Hi
I mean that, can we invoke the bpf_jit_dump in test_bpf.ko directly ?. bpf_prog_get_info_by_fd copy the insn to userspace, but we only dump insn in test_bpf.ko

                if (bpf_dump_raw_ok(file->f_cred)) {// code copied from bpf_prog_get_info_by_fd, not tested

                        /* for multi-function programs, copy the JITed
                         * instructions for all the functions
                         */
                        if (prog->aux->func_cnt) {
                                for (i = 0; i < prog->aux->func_cnt; i++) {
                                        len = prog->aux->func[i]->jited_len;
                                        img = (u8 *) prog->aux->func[i]->bpf_func;
                                        bpf_jit_dump(1, len, 1, img);
                                }
                        } else {
                                bpf_jit_dump(1, ulen, 1, prog->bpf_func);
                        }
                }


 




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