[bpf-next v2] bpf: drop deprecated bpf_jit_enable == 2
Tonghao Zhang
tong at infragraf.org
Wed Jan 18 01:18:36 AEDT 2023
> On Jan 17, 2023, at 7:36 PM, Christophe Leroy <christophe.leroy at csgroup.eu> wrote:
>
>
>
> Le 17/01/2023 à 08:30, Christophe Leroy a écrit :
>>
>>
>> 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.
>
> Hi Again,
>
> I tested again, the problem is still the same as one year ago:
>
> root at vgoip:~# ./bpftool prog
> libbpf: elf: endianness mismatch in pid_iter_bpf.
It seem to be not right ehdr->e_ident[EI_DATA]. Do we can print the real value?
/*
* e_ident[EI_DATA]
*/
#define ELFDATANONE 0
#define ELFDATA2LSB 1
#define ELFDATA2MSB 2
#define ELFDATANUM 3
bpf_object__elf_init:
obj->efile.ehdr = ehdr = elf64_getehdr(elf);
> libbpf: failed to initialize skeleton BPF object 'pid_iter_bpf': -4003
> Error: failed to open PID iterator skeleton
>
> root at vgoip:~# uname -a
> Linux vgoip 6.2.0-rc3-02596-g1c2c9c13e256 #242 PREEMPT Tue Jan 17
> 09:36:08 CET 2023 ppc GNU/Linux
On my pc, elf is little endian.
# readelf -h tools/bpf/bpftool/pid_iter.bpf.o
ELF Header:
Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian # x86_64
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: REL (Relocatable file)
Machine: Linux BPF
Version: 0x1
Entry point address: 0x0
Start of program headers: 0 (bytes into file)
Start of section headers: 64832 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 0 (bytes)
Number of program headers: 0
Size of section headers: 64 (bytes)
Number of section headers: 13
Section header string table index: 1
>
>>
>> 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 ?
>>
>> Thanks
>> Christophe
>>
>
>
> Christophe
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