On Mon, May 03, 2021 at 12:08:02PM +0200, 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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>
Just disabling the ftrace filter in pahole does not seem to fix it.
Is there some other place where it should be disabled?
Thanks
Michal
