[bpf-next v2] bpf: drop deprecated bpf_jit_enable == 2
Tonghao Zhang
tong at infragraf.org
Wed Jan 18 13:13:11 AEDT 2023
> On Jan 17, 2023, at 11:59 PM, Daniel Borkmann <daniel at iogearbox.net> wrote:
>
> On 1/17/23 3:22 PM, Tonghao Zhang wrote:
>>> On Jan 17, 2023, at 3:30 PM, Christophe Leroy <christophe.leroy at csgroup.eu> wrote:
>>>
>>>
>>>
>>> Le 17/01/2023 à 06:30, Tonghao Zhang a écrit :
>>>>
>>>>
>>>>> On Jan 9, 2023, at 4:15 PM, Christophe Leroy <christophe.leroy at csgroup.eu> 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 at infragraf.org a écrit :
>>>>>>>> From: Tonghao Zhang <tong at infragraf.org>
>>>>>>>>
>>>>>>>> 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@arm.com/#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);
}
}
More information about the Linuxppc-dev
mailing list