Re: FYI: CI regression on big-endian arch (s390) after recent pahole changes

[Song Liu <songliubraving@meta.com>]

Hi Eduard, 

Thanks for sending the report!

> On Aug 29, 2024, at 5:05 PM, Eduard Zingerman <eddyz87@gmail.com> wrote:
> 
> Hi Arnaldo, Alan,
> 
> After recent pahole changes [1] BPF CI fails for s390 [2].
> Song Liu identified that there is a mismatch between endianness of BTF
> in .BTF and .BTF.base sections.

Clarification: 

With the regression, _both_ .BTF and .BTF.base sections (or at 
least part of these sections) are in little endian for s390:

$ objdump -s -j .BTF bpf_testmod.ko | head
bpf_testmod.ko:     file format elf64-big

Contents of section .BTF:
 0000 9feb0100 18000000 00000000 301a0000  ............0...
 0010 301a0000 80110000 00000000 0000000a  0...............
 0020 24000000 00000000 00000003 00000000  $...............
 0030 28000000 06000000 2b000000 00000000  (.......+.......
 0040 0000000a 29000000 ea010000 03000004  ....)...........
 0050 18000000 04020000 1e010000 00000000  ................

$ objdump -s -j .BTF.base bpf_testmod.ko | head
bpf_testmod.ko:     file format elf64-big

Contents of section .BTF.base:
 0000 9feb0100 18000000 00000000 fc010000  ................
 0010 fc010000 ea010000 01000000 00000001  ................
 0020 08000000 40000000 13000000 00000001  ....@...........
 0030 01000000 08000000 18000000 00000001  ................
 0040 04000000 20000000 25000000 00000001  .... ...%.......
 0050 01000000 08000001 31000000 00000001  ........1.......



Before the regression, the "9feb" part was "eb9f" for s390:

$ objdump -s -j .BTF bpf_testmod.ko | head
bpf_testmod.ko:     file format elf64-big

Contents of section .BTF:
 0000 eb9f0100 00000018 00000000 00001560  ...............`
 0010 00001560 00000fc2 00000000 0a000000  ...`............


Thanks,
Song