2023-01-17 14:25 UTC+0000 ~ Christophe Leroy [off-list ref]

Le 17/01/2023 à 15:18, Tonghao Zhang a écrit :

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On Jan 17, 2023, at 7:36 PM, Christophe Leroy [off-list ref] wrote:



Le 17/01/2023 à 08:30, Christophe Leroy a écrit :

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Le 17/01/2023 à 06:30, Tonghao Zhang a écrit :

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On Jan 9, 2023, at 4:15 PM, Christophe Leroy
[off-list ref] wrote:

[...]

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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!

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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);

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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

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