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

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Le 17/01/2023 à 15:18, Tonghao Zhang a écrit :
> 
> 
>> On Jan 17, 2023, at 7:36 PM, Christophe Leroy <christophe.leroy@xxxxxxxxxx> 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@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.
>>
>> Hi Again,
>>
>> I tested again, the problem is still the same as one year ago:
>>
>> root@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@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
> 

Yes, must be something wrong with the build, I get same as you :

$ LANG= readelf -h 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
   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:          34704 (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


Whereas I expect the same as bpftool I suppose, which is :

$ LANG= readelf -h bpftool
ELF Header:
   Magic:   7f 45 4c 46 01 02 01 00 00 00 00 00 00 00 00 00
   Class:                             ELF32
   Data:                              2's complement, big endian
   Version:                           1 (current)
   OS/ABI:                            UNIX - System V
   ABI Version:                       0
   Type:                              EXEC (Executable file)
   Machine:                           PowerPC
   Version:                           0x1
   Entry point address:               0x100027d0
   Start of program headers:          52 (bytes into file)
   Start of section headers:          1842896 (bytes into file)
   Flags:                             0x0
   Size of this header:               52 (bytes)
   Size of program headers:           32 (bytes)
   Number of program headers:         9
   Size of section headers:           40 (bytes)
   Number of section headers:         39
   Section header string table index: 38


Thanks
Christophe




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