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

[Quentin Monnet]

2023-01-17 14:25 UTC+0000 ~ Christophe Leroy <christophe.leroy at csgroup.eu>
> 
> 
> Le 17/01/2023 à 15:18, Tonghao Zhang a écrit :
>>
>>
>>> 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:

[...]

>>>>>> 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=

Christophe, apologies from dropping the discussion the last time, it
seems your last message on that thread didn't make it to my inbox at the
time :/. Thanks a lot for looking into that again!

>>>>> 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
>>
> 
> 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
> 

pid_iter.bpf.o should be generated from that command in bpftool's Makefile:

	$(OUTPUT)%.bpf.o: skeleton/%.bpf.c $(OUTPUT)vmlinux.h \
			$(LIBBPF_BOOTSTRAP)
		$(QUIET_CLANG)$(CLANG) \
			-I$(or $(OUTPUT),.) \
			-I$(srctree)/tools/include/uapi/ \
			-I$(LIBBPF_BOOTSTRAP_INCLUDE) \
			-g -O2 -Wall -fno-stack-protector \
			-target bpf -c $< -o $@

My understanding is that "-target bpf" is supposed to pick the
endianness for the host (see "llc --version | grep bpf". If that's not
the case, could you please try to turn that into '-target bpfeb' in the
Makefile instead? I'd be curious to see if it helps.

Quentin