On 03. 05. 21, 12:08, Jiri Olsa wrote:
> On Mon, May 03, 2021 at 10:59:44AM +0200, Jiri Slaby wrote:
>> CCing pahole people.
>>
>> On 03. 05. 21, 9:59, Jiri Slaby wrote:
>>> On 03. 05. 21, 8:11, Jiri Slaby wrote:
>>>>>>>>> looks like vfs_truncate did not get into BTF data,
>>>>>>>>> I'll try to reproduce
>>>>>
>>>>> _None_ of the functions are generated by pahole -J from
>>>>> debuginfo on ppc64. debuginfo appears to be correct. Neither
>>>>> pahole -J fs/open.o works correctly. collect_functions in
>>>>> dwarves seems to be defunct on ppc64... "functions" array is
>>>>> bogus (so find_function -- the bsearch -- fails).
>>>>
>>>> It's not that bogus. I forgot an asterisk:
>>>>> #0  find_function (btfe=0x100269f80, name=0x10024631c
>>>>> "stream_open") at
>>>>> /usr/src/debug/dwarves-1.21-1.1.ppc64/btf_encoder.c:350
>>>>> (gdb) p (*functions)@84
>>>>> $5 = {{name = 0x7ffff68e0922 ".__se_compat_sys_ftruncate", addr
>>>>> = 75232, size = 72, sh_addr = 65536, generated = false}, {
>>>>>      name = 0x7ffff68e019e ".__se_compat_sys_open", addr = 80592,
>>>>> size = 216, sh_addr = 65536, generated = false}, {
>>>>>      name = 0x7ffff68e0076 ".__se_compat_sys_openat", addr =
>>>>> 80816, size = 232, sh_addr = 65536, generated = false}, {
>>>>>      name = 0x7ffff68e0908 ".__se_compat_sys_truncate", addr =
>>>>> 74304, size = 100, sh_addr = 65536, generated = false}, {
>>>> ...
>>>>>      name = 0x7ffff68e0808 ".stream_open", addr = 65824, size =
>>>>> 72, sh_addr = 65536, generated = false}, {
>>>> ...
>>>>>      name = 0x7ffff68e0751 ".vfs_truncate", addr = 73392, size =
>>>>> 544, sh_addr = 65536, generated = false}}
>>>>
>>>> The dot makes the difference, of course. The question is why is it
>>>> there? I keep looking into it. Only if someone has an immediate
>>>> idea...
>>>
>>> Well, .vfs_truncate is in .text (and contains an ._mcount call). And
>>> vfs_truncate is in .opd (w/o an ._mcount call). Since setup_functions
>>> excludes all functions without the ._mcount call, is_ftrace_func later
>>> returns false for such functions and they are filtered before the BTF
>>> processing.
>>>
>>> Technically, get_vmlinux_addrs looks at a list of functions between
>>> __start_mcount_loc and __stop_mcount_loc and considers only the listed.
>>>
>>> I don't know what the correct fix is (exclude .opd functions from the
>>> filter?). Neither why cross compiler doesn't fail, nor why ebi v2 avoids
>>> this too.
>>
>> Attaching a patch for pahole which fixes the issue, but I have no idea
>> whether it is the right fix at all.
> 
> hi,
> we're considering to disable ftrace filter completely,
> I guess that would solve this issue for ppc as well
> 
>    https://lore.kernel.org/bpf/20210501001653.x3b4rk4vk4iqv3n7@kafai-mbp.dhcp.thefacebook.com/

Right, the attached patch fixes it for me too.

-- 
js